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General Science => General Science => Topic started by: jerrygg38 on 14/08/2016 19:21:31

Title: What is centrifugal force?
Post by: jerrygg38 on 14/08/2016 19:21:31
What is centrifugal force?
  In the previous discussion Alancalverd stated that there was no such thing as centrifugal force. Thus it is just a way of expressing the resultant force tending to push an object away from a string or a gravitational force. It appears that there are two different but similar cases. In the case of a string, the object spinning around a center point wants to go in a straight line. The string prevents this and you end up with a vector problem in which the string has actual centripetal force acting from the center point. This is just simple mechanical engineering 101.
  Now let us look at the Earth spinning around the sun. For simplicity we can say that the ellipse is basically a circle although the equations are the similar. There is no longer a string between the earth and the sun. The simple vector forces of the spinning ball on a rope do not apply but the answers are basically the same. Thus we can say that we have a gravitational centripetal force and a gravitational centrifugal force. This is a much more complex scientific problem.  Since there is no rope between sun and earth, space itself must act to produce the force of attraction.
  However it is not really possible to conceive that space produces an attractive force. The only explanation is that space pushes the Earth and sun together. Einstein produced his general relativity equations to account for the action of space upon the sun and Earth. The pushing together of earth and sun is self-evident to me. So there is no such thing as centripetal force. It is just a mathematical tool.
   Then we are left with centrifugal force. The earth and sun interact by their gravitational fields.  As the earth moves around the sun the earth wants to move in a straight line. At the same time the two gravitational fields tend to combine and set up a combined center. These fields exist further out in space and the net result is the earth is pushed toward the sun and visa-versa. At the same time the sun wobbles around its axis since the center of gravity of the earth/sun combination keeps moving.  Of course the other planets make the wobble of the sun more complex.
  As the Earth moves in a linear fashion and is pushed toward the sun, the earth’s gravitational field tends to push against the sun’s gravitational field. This causes the combined field to look like a circular railroad track. The static fields tend to push the earth toward the sun but the dynamic fields tend to push the earth away from the sun.
  We then have the centripetal force due to the static gravitational forces which tend to bring both earth and sun to a common center point and the centrifugal forces which are dynamic and tend to push the earth away from the sun. These equal and opposite forces then are very similar to the ball and string problem.
    Anyway the previous response by Alancaverd got me to thinking about the centrifugal force. What do you guys think of this analysis?
Title: Re: What is centrifugal force?
Post by: alancalverd on 15/08/2016 23:13:07
I never said it didn't exist! I'm a scientist, for heaven's sake, not a writer of science textbooks!

Centrifugal force is what separates liquids in a centrifuge. If there was only a centripetal force, the liquid would all rise out of the test tube and splash around  in the middle of the machine. Centrifugal force is what keeps "wall of death" riders stuck to the inside of the cage instead of collapsing in a heap at the bottom. Whan yo black out in a high-g turn, is it because your head is being pulled into the middle of the turn, or because your blood is being squeezed outwards? Does the centripetal force shrink the wheel, or does the centrifugal force expand the tyre? It is the radial outward force on a body that follows a curved path.

If you whirl a stone around on a string, you can feel the outward tension in the string. It must be outward because a string can't push, any more than a liquid can pull.

Idiot textbook writers say "but if you cut the string, the stone moves at a tangent, not a radius, so there can't be a radial force". I say "if you cut the string, the stone is no longer constrained to move in a curved path, so Newton's first law applies - the body continues to move in a straight line, which is obviously the tangent at the point of cutting."

This is the kind of nonsense that pays philosphers' salaries, and should therefore be banned from polite conversation.
Title: Re: What is centrifugal force?
Post by: jerrygg38 on 16/08/2016 11:13:12
I never said it didn't exist! I'm a scientist, for heaven's sake, not a writer of science textbooks!

Centrifugal force is what separates liquids in a centrifuge. If there was only a centripetal force, the liquid would all rise out of the test tube and splash around  in the middle of the machine. Centrifugal force is what keeps "wall of death" riders stuck to the inside of the cage instead of collapsing in a heap at the bottom. Whan yo black out in a high-g turn, is it because your head is being pulled into the middle of the turn, or because your blood is being squeezed outwards? Does the centripetal force shrink the wheel, or does the centrifugal force expand the tyre? It is the radial outward force on a body that follows a curved path.

If you whirl a stone around on a string, you can feel the outward tension in the string. It must be outward because a string can't push, any more than a liquid can pull.

Idiot textbook writers say "but if you cut the string, the stone moves at a tangent, not a radius, so there can't be a radial force". I say "if you cut the string, the stone is no longer constrained to move in a curved path, so Newton's first law applies - the body continues to move in a straight line, which is obviously the tangent at the point of cutting."

This is the kind of nonsense that pays philosphers' salaries, and should therefore be banned from polite conversation.
  Thanks for the clarification of your beliefs. You had said ""Modern" textbooks insist that there is no such thing as centrifugal force.

This is a great comfort to mechanical engineers, who can now spin wheels as fast as they like without the tyres coming off or the grinding wheel bursting.

It is however worrying to know that the tension you feel when you whirl an object around on a string, or the phenomenon that makes you black out in a tight aerobatic turn (just before the wings fall off)  is a figment of your outdated imagination. "

   Your words had confused me as to your beliefs. Now you clarified them so you believe that the modern textbook writers are idiots in their beliefs. I had never read a modern textbook as most of my studies involved my old textbooks and whatever new data I got from the internet or various articles.
  So now I am still left with wondering why the writers of the textbooks believe that centrifugal force does not exist.
   The rope and the string doesn't need a centrifugal force because the sting constrains the motion of the length of the string. In this case the centrifugal force does not have to exist but is merely a vector caused by the momentum of the ball and the length of the string.
  The earth spinning around the sun is different. There is no string so the centrifugal force is not easily identified. You have a momentum and a gravitational pressure pushing the earth toward the sun. What keeps the earth from falling into the sun?  That is the big problem.
  So we get a law of physics such that "A planet moving with velocity V tangent to the radius from a star will generate a centrifugal force that balances the centripetal force and this keeps the planet from falling into the star".
  The question is why does this law happen. To say it happens is fine. It is just a law. But as an engineer I want to understand why it happens.
 From an electrical perspective we could say that the planets gravitational field cuts the stars gravitational field and this produces a gravitational gradient vector. Thus the centrifugal force is an induced gravitational field that is equal and opposite to the main gravitational field attraction.
   As I look at the moon and the earth, it is self evident to me that the moon is phase locked to the Earth. This is an electrical type term. The Earths gravitational field is cutting the moon and producing eddy type gravitational currents within the moon. This slowly brings the moon to a standstill and we only see one face of the moon.
  The question is whether Einstein and others have considered what happens when one gravitational field cuts another field during orbital motion? Do gravitational eddy currents exist? I believe they do. What do you think?
Title: Re: What is centrifugal force?
Post by: Colin2B on 17/08/2016 09:01:41
Many textbooks only give half the story. The interesting thing about forces like centrifugal and Coriolis is that they are frame dependant. From an inertial frame there is no force but just the relative movement of two objects. However, from the rotating frame - the car on a bend, the child on the roundabout, the tension in the string - the force is very real and obvious.
Title: Re: What is centrifugal force?
Post by: jeffreyH on 17/08/2016 10:43:57
In simplistic terms F = ma. A change in vector direction is an acceleration. Therefore you have a force. Why the confusion?
Title: Re: What is centrifugal force?
Post by: jerrygg38 on 19/08/2016 12:08:00
In simplistic terms F = ma. A change in vector direction is an acceleration. Therefore you have a force. Why the confusion?
   That is true. But the questions is why? What is the physical mechanism that produces the force? Mathematical laws are nice but do we live in a mathematical universe or a physical universe?  If we live in a mathematical universe then the above equation is fine. If we live in a physical universe then what is the physical reason for centrifugal force.
  So if we look at a spinning mass such as  planet Saturn we find rings that are spinning around in a plane. The rings are held by gravity and counterbalanced by centrifugal force.
  Two things are at play. There is the mass of Saturn and the gravitational field of Saturn. For this case the effect of the sun or other planets is small. The centrifugal force acting upon the rings is an interaction between the small gravitational fields of all the tiny particles and the larger gravitational field of Saturn.
   As I see it, the physical reason for the centrifugal force is due to the motion of the tiny particle fields and the larger field of Saturn. The mathematical law may be fine but the reason for the law is a more complex field problem. what do you think?
Title: Re: What is centrifugal force?
Post by: PhysBang on 19/08/2016 12:44:18
This is the kind of nonsense that pays philosphers' salaries, and should therefore be banned from polite conversation.
There are many philosophers that can do physics far, far better than you, so perhaps you should refrain from attacking philosophers in general.

The reason that people say that there is no centrifugal force is that there is no source for the force other than the centripetal force involved and inertia.
In simplistic terms F = ma. A change in vector direction is an acceleration. Therefore you have a force. Why the confusion?
In this case, the the vector decomposition is into inertia and centripetal force, there is no separate centrifugal source.
Title: Re: What is centrifugal force?
Post by: jeffreyH on 19/08/2016 13:06:02
This is the kind of nonsense that huh uh pays philosphers' salaries, and should therefore be banned from polite conversation.
There are many philosophers that can do physics far, far better than you, so perhaps you should refrain from attacking philosophers in general.

The reason that people say that there is no centrifugal force is that there is no source for the force other than the centripetal force involved and inertia.
In simplistic terms F = ma. A change in vector direction is an acceleration. Therefore you have a force. Why the confusion?
In this case, the the vector decomposition is into inertia and centripetal force, there is no separate centrifugal source.

Define the system(s) for which this is true.
Title: Re: What is centrifugal force?
Post by: jerrygg38 on 19/08/2016 15:40:32

The reason that people say that there is no centrifugal force is that there is no source for the force other than the centripetal force involved and inertia.

  I just posted my understanding of :Why does a mass move in a straight line and with constant velocity"  in new theories which should help to explain the centrifugal force. In my latest thoughts It is a force due to the motion of an object in relation to its own gravitational field.
Title: Re: What is centrifugal force?
Post by: alancalverd on 20/08/2016 00:09:26
Quote
There are many philosophers that can do physics far, far better than you, so perhaps you should refrain from attacking philosophers in general.
I am flattered that you know how good I am, and surprised that you did not name a philosopher who can do my job better - the profession is not known for modesty.

Quote
The reason that people say that there is no centrifugal force is that there is no source for the force other than the centripetal force involved and inertia.
which is why nobody blacks out during aerobatics, and tyres do not come off wheels at high speed? In my universe, something is opposing the arterial flow to my brain and some outward force is expanding the tyres.
Title: Re: What is centrifugal force?
Post by: jerrygg38 on 20/08/2016 11:42:39
AlanCalverd said about centrifugal force
"which is why nobody blacks out during aerobatics, and tyres do not come off wheels at high speed? In my universe, something is opposing the arterial flow to my brain and some outward force is expanding the tyres."
  It is easy to spin a ball on a string and feel the pull. Likewise when you drive your car on a curve you can feel the results. In addition they bank the curves on racetracks to prevent the cars from going out of control. To me it appears that the centrifugal force is an actual force rather than a resultant vector of linear motion and a perpendicular attractive force. Perhaps the resulting force is the result of the cutting of the earths gravitational field by the moving objects gravitational field. Then we get two different ways of looking at the same problem. One would think that the mathematicians would have come up with this type of analysis already.
Title: Re: What is centrifugal force?
Post by: puppypower on 20/08/2016 12:00:24
In a Newtonian sense, for every action there is a reaction. Centrifugal force appears to be a reactive force, to a constraining force, that is acting perpendicular to the direction of velocity.

In terms of relativity, gravity as defined by General Relativity, causes space-time to curve. In the case of an orbit, is the centrifugal force a reaction to GR and the curvature of space-time? If we orbited a neutron star, we would feel the centrifugal force.

If we have a weight on a string being moved in an orbit, a restraining force is causing the velocity to accelerate; change direction. This is felt as centrifugal force. If we cut the string, to remove the restraining force, the weigh continues on in straight line. If the restraining force was gravity; GR, is the straight line implicit of zero curvature space-time?

We use the moons and planets to sling shot satellites to distant planets. We make use of the centrifugal force, returning the probe to zero curvature space-time, between the centrifugal force induced by the GR of each planet or moon. Does velocity use an absolute reference of zero space-time curvature, if the centrifugal force is zero; string is cut?

Velocity is d/t, while acceleration is d/t/t. The centrifugal force contains extra units of time; potential, relative to velocity. When this time potential is zero, there is no curvature in space-time; pure velocity.
Title: Re: What is centrifugal force?
Post by: jerrygg38 on 20/08/2016 14:27:38
In a Newtonian sense, for every action there is a reaction. Centrifugal force appears to be a reactive force, to a constraining force, that is acting perpendicular to the direction of velocity.

In terms of relativity, gravity as defined by General Relativity, causes space-time to curve. In the case of an orbit, is the centrifugal force a reaction to GR and the curvature of space-time?
Velocity is d/t, while acceleration is d/t/t. The centrifugal force contains extra units of time; potential, relative to velocity. When this time potential is zero, there is no curvature in space-time; pure velocity.

  The problem with your words is that you say General
Relativity causes space time to curve. How can general relativity cause space time to curve? Why? This makes no sense. Somehow there is a Sky God called "general relativity" that causes planets and photons, etc. to move in curved paths. This is pure magic and very unscientific for sure. The mathematicians may be happy so say such things but as an Engineer I do not believe it. To be more truthful, general relativity is a mathematical theory which is able to accurately calculate measurements of the universe. Thus it is a true mathematical approximation to reality. However general relativity causes nothing at all. Thus the answers I seek is to understand why Einsteins math works well.
Title: Re: What is centrifugal force?
Post by: PhysBang on 20/08/2016 14:58:18
In simplistic terms F = ma. A change in vector direction is an acceleration. Therefore you have a force. Why the confusion?
   That is true. But the questions is why? What is the physical mechanism that produces the force? Mathematical laws are nice but do we live in a mathematical universe or a physical universe?  If we live in a mathematical universe then the above equation is fine. If we live in a physical universe then what is the physical reason for centrifugal force.
  So if we look at a spinning mass such as  planet Saturn we find rings that are spinning around in a plane. The rings are held by gravity and counterbalanced by centrifugal force.
  Two things are at play. There is the mass of Saturn and the gravitational field of Saturn. For this case the effect of the sun or other planets is small. The centrifugal force acting upon the rings is an interaction between the small gravitational fields of all the tiny particles and the larger gravitational field of Saturn.
   As I see it, the physical reason for the centrifugal force is due to the motion of the tiny particle fields and the larger field of Saturn. The mathematical law may be fine but the reason for the law is a more complex field problem. what do you think?
This is so horribly wrong. The rings are held in place by centripetal force.
Title: Re: What is centrifugal force?
Post by: PhysBang on 20/08/2016 14:59:05
Define the system(s) for which this is true.
Define?

I can tell you the ones for which they are true: every planet in the solar system. Every galaxy.
Title: Re: What is centrifugal force?
Post by: jeffreyH on 20/08/2016 15:39:31
Define the system(s) for which this is true.
Define?

I can tell you the ones for which they are true: every planet in the solar system. Every galaxy.

Ok so we can define gravitation as a system with no centrifugal force. Any others?
Title: Re: What is centrifugal force?
Post by: PhysBang on 20/08/2016 18:11:31
Ok so we can define gravitation as a system with no centrifugal force. Any others?
I don't think you get it.

The great theory of Newton on gravity is that what holds the planets in orbit is the force of gravity acting on them directing them towards, roughly, the sun.

Centrifugal force is the force supposedly directed outwards away from the center due to rotation. This is, in all cases, due to the equal and opposite reaction of being diverted towards a center from otherwise linear motion.
Title: Re: What is centrifugal force?
Post by: jeffreyH on 20/08/2016 18:17:41
Ok so we can define gravitation as a system with no centrifugal force. Any others?
I don't think you get it.

The great theory of Newton on gravity is that what holds the planets in orbit is the force of gravity acting on them directing them towards, roughly, the sun.

OK that's the centripetal force.

Quote
Centrifugal force is the force supposedly directed outwards away from the center due to rotation. This is, in all cases, due to the equal and opposite reaction of being diverted towards a center from otherwise linear motion.

OK So define systems not related to gravity.
Title: Re: What is centrifugal force?
Post by: PhysBang on 20/08/2016 18:56:20
OK So define systems not related to gravity.
You keep using the word "define", but I don't think it means what you think it means.

Think of the device called a "centrifuge". This device spins and imparts a linear velocity on the contents of the vessel(s) in the device, but the contents are diverted from their course by the electromagnetic forces holding the device in its solid form.
Title: Re: What is centrifugal force?
Post by: jeffreyH on 20/08/2016 19:14:00
OK So define systems not related to gravity.
You keep using the word "define", but I don't think it means what you think it means.

Think of the device called a "centrifuge". This device spins and imparts a linear velocity on the contents of the vessel(s) in the device, but the contents are diverted from their course by the electromagnetic forces holding the device in its solid form.

This is not a trivial point. We have a definition of ficticious or pseudo force which covers centrifugal force. I have seen it stated at times that gravity is a fictitious force. That magical changes in geometry cause gravity. Therefore I believe it is important to nail down a definition.
Title: Re: What is centrifugal force?
Post by: jerrygg38 on 20/08/2016 19:39:02
Ok so we can define gravitation as a system with no centrifugal force. Any others?
I don't think you get it.

The great theory of Newton on gravity is that what holds the planets in orbit is the force of gravity acting on them directing them towards, roughly, the sun.

Centrifugal force is the force supposedly directed outwards away from the center due to rotation. This is, in all cases, due to the equal and opposite reaction of being diverted towards a center from otherwise linear motion.
  The equal and opposite reaction may be true but what does it mean? Centrifugal force is equal and opposite to centripetal force is something we can memorize but it lacks meaning. What is the mechanism by which it is true? The basic understanding of physics is lacking. All we have are rules to remember. And I for one want to know why!
Title: Re: What is centrifugal force?
Post by: hamdani yusuf on 24/08/2016 02:19:21
Ok so we can define gravitation as a system with no centrifugal force. Any others?
I don't think you get it.

The great theory of Newton on gravity is that what holds the planets in orbit is the force of gravity acting on them directing them towards, roughly, the sun.

Centrifugal force is the force supposedly directed outwards away from the center due to rotation. This is, in all cases, due to the equal and opposite reaction of being diverted towards a center from otherwise linear motion.
  The equal and opposite reaction may be true but what does it mean? Centrifugal force is equal and opposite to centripetal force is something we can memorize but it lacks meaning. What is the mechanism by which it is true? The basic understanding of physics is lacking. All we have are rules to remember. And I for one want to know why!
Centrifugal force emerges when there are strength difference in centripetal forces working on parts of a system.
In a turning moving car, the road forces the wheels sideway which in turn forces other parts of the car which is then felt by the passengers. The passengers don't receive any force directly from the road.
In ISS, the earth forces each part almost equally, including every atoms of its passengers. That's why they don't feel the centrifugal force even though centripetal force done by the earth to them through gravity is comparable to the turning car.
Title: Re: What is centrifugal force?
Post by: PmbPhy on 24/08/2016 13:25:42
Quote from: jerrygg38
What is centrifugal force?
Simply put, centrifugal force is an inertial force. If you're at rest in a rotating frame of reference then objects which are moving with no acceleration in the inertial frame will accelerate in your frame.

You can read more about inertial forces on my website at:
http://www.newenglandphysics.org/physics_world/gr/inertial_force.htm
Title: Re: What is centrifugal force?
Post by: jerrygg38 on 24/08/2016 14:15:04
hamdani yusuf said:
In ISS, the earth forces each part almost equally, including every atoms of its passengers. That's why they don't feel the centrifugal force even though centripetal force done by the earth to them through gravity is comparable to the turning car.
You raise an interesting point. Why don't we feel the rotation of the Earth? You say that everything upon the earth has equal forces on it. In other words, you need differential forces to feel the centrifugal force.
Thus the Earth itself has a centrifugal force relative to the sun. It may be that our atmosphere acts a counterbalance to our centrifugal forces. If the Earth spun faster and faster each second, then perhaps we would notice this force.
   In the space station, they are moving fast but they do not experience being pushed against the outer side of the cabin. Thus again they are subject to the same force as the space station but they are inside the station. So they feel nothing. The space station as a whole feels the centrifugal force.
 
Title: Re: What is centrifugal force?
Post by: jerrygg38 on 24/08/2016 14:23:39
To all:
  It seems to me at the moment that centrifugal force is similar to the force that occurs when you try to rotate a gyroscope slightly perpendicular to its axis. It is beginning to seem to me that it is not a fancy space time force but a simple internal force that originates within the object itself. Any other ideas from the world of science?
Title: Re: What is centrifugal force?
Post by: hamdani yusuf on 24/08/2016 15:09:04
We don't feel earth rotation because it is too slow for our senses.
Title: Re: What is centrifugal force?
Post by: alancalverd on 24/08/2016 17:38:36
Why don't we feel the rotation of the Earth?

We do.

Quote
Because of a planet's rotation around its own axis, the [net] gravitational acceleration is less at the equator than at the poles. In the 17th century, following the invention of the pendulum clock, French scientists found that clocks sent to French Guiana, on the northern coast of South America, ran slower than their exact counterparts in Paris.
Title: Re: What is centrifugal force?
Post by: jerrygg38 on 25/08/2016 13:38:07
Why don't we feel the rotation of the Earth?

We do.

Quote
Because of a planet's rotation around its own axis, the [net] gravitational acceleration is less at the equator than at the poles. In the 17th century, following the invention of the pendulum clock, French scientists found that clocks sent to French Guiana, on the northern coast of South America, ran slower than their exact counterparts in Paris.
  The force is MV^2/R where the rotational velocity is around 1000 miles per hour and the distance to the center of the Earth is around 4000 miles. So I guess this is small.
  As far as the gravitational acceleration on different points of the Earth, the programmers of my 5 inch gun system took this into account as the various forces operating upon the Earth had to be accounted for to insure accuracy. I was the hardware designer but the physicists and programmers took so many things into account including air pressure.
Title: Re: What is centrifugal force?
Post by: rmolnav on 02/10/2016 19:48:41
SOME of you base your arguments on the idea that c. f. is not actually real.
Last year I defended the opposite, in more than one "subject", particularly in the one relative to the existence of 4 high tides a day, instead of just 2.
I did it gaving many examples. Now just a very simple one:
Imagine you are rotating a weight, with the help of your hand (and wrist) and a string. Somebody has already put this case.
Let us put a dynamometer between weight and string. It will show the centripetal f. that is producing the rotational movement (the dynamometer pulling the weight).
But the ACTION AND REACTION principle says that if that mentioned force exist,  the weight is also pulling the dynamometer with another opposite and equal force. That is a REAL force, and CENTRIFUGAL.
By the way, the same could be said in relation with the knot between the string and the dynamometer ... And this instrument functions with two opposite forces applied at its extremes. At the inner one it would be the centripetal force (the string pulls inwards the dynamometer ), and at the outer one the centripetal force (the weight pulls outwards the dynamometer)
Title: Re: What is centrifugal force?
Post by: rmolnav on 04/10/2016 12:10:47
#28 (continuation)
Sorry I erroneously said "4 high tides a day, instead of just 2". Logically it should be 2 instead of 1.
Perhaps I was thinking in the fact that, being tides produced mainly by Moon, but also by Sun, there are actually 2 high tide bulges due to Moon, and 2 due to Sun. But both tidal effects are seen added, and the result is just 2 high tides syncronized to Moon position. The Sun tide result is the oscillation in tidal coefficient, according to Sun/Moon relative position.
Title: Re: What is centrifugal force?
Post by: hamdani yusuf on 04/10/2016 14:06:52
Imagine a weight floating in space far away from anything else. Let us put a dynamometer between the weight and a string.
If the string is pulled the dynamometer will register a value, which is indicating that opposing forces are acting on its ends.
The question is, what force is acting on the dynamometer from the weight's side?
Title: Re: What is centrifugal force?
Post by: rmolnav on 04/10/2016 18:58:54
#30
The string pull would produce an acceleration of both dynamometer and weight. After some transient situation, if somehow the string pull keeps constant, the acceleration of the weight would continue. That means the dynamometer is pulling the weight, and due to action and reaction principle the weight would also be pulling the weight, with equal but opposite force.
By the way, the force shown by the dynamometer would be not only the mass of the weight times the acceleration ... The mass of the dynamometer times the acceleration should be added.
Title: Re: What is centrifugal force?
Post by: rmolnav on 04/10/2016 19:46:46
#24
Not bad idea. Those orce and torque are reactions to others that are trying to change movements that, due to the inertia of objects, without any force/torque would keep with a kind of constant movement.
In one case the movement "tries" to maintain its velocity vector (value and straight line of movement), and the gyroscope tries to keep constant its angular momentum vector (value of angular speed and direction, both of vector and perpendicular planes of movement of all parts of the gyroscope) 
Title: Re: What is centrifugal force?
Post by: hamdani yusuf on 05/10/2016 07:20:52
Newton's laws of motion are three physical laws that, together, laid the foundation for classical mechanics. They describe the relationship between a body and the forces acting upon it, and its motion in response to those forces. They have been expressed in several different ways, over nearly three centuries,[1] and can be summarised as follows.

First law: In an inertial reference frame, an object either remains at rest or continues to move at a constant velocity, unless acted upon by a net force.[2][3]
Second law: In an inertial reference frame, the sum of the forces F on an object is equal to the mass m of that object multiplied by the acceleration a of the object: F = ma.
Third law: When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body.

According to Newton's Law, something is called force if it can produce acceleration. If mass is considerably constant, force is what is needed to change an object's velocity.

In linear acceleration like my example above, the dynamometer reads a value because the weight has inertia which then produce reactional force. It doesn't accelerate the weight to the opposite direction of the pull on the string, i.e. if the pull is stopped, the weight won't reverse the acceleration.
The analogy is applicable for angular acceleration, which requires a centripetal force. The centrifugal force is merely reactional, due to the inertia of the weight. If the centripetal force is stopped, the weight won't accelerate away from the center of the rotation, but merely continue with the latest velocity.
Title: Re: What is centrifugal force?
Post by: rmolnav on 05/10/2016 21:29:16
#33
Thank you for putting it that clear. Just a short comment, mainly aimed to others.
You say:
"If the centripetal force is stopped, the weight won't accelerate away from the center of the rotation, but merely continue with the latest velocity".
Right, but that doesn´t mean, as others say, that centrifugal force doesn´t exist, that it is only kind of sensation due the "natural" tendency of the rotating object to follow the tangent ...
As long as the centripetal force "starts", the object otherwise moving in a straight line, suffers ONLY that force, and consequently a centripetal acceleration that makes it rotate. The centrifugal one is the reaction exerted ON THE STRING (or the dynamometer if installed) by the weight.
Should the string brake, logically both centripetal force and its reaction (centrifugal) suddenly go to null. The previously rotating objects follows the tangent (dynamometer included if braking point is more inside), and the string falls down due to its own weight. Weights of considered objects have not being considered, supposing that are rather negligible compared to other acting forces. It only would mean that the string would shape a short cone instead of a perfect circle, but this doesn´t change our arguments.   
Title: Re: What is centrifugal force?
Post by: puppypower on 06/10/2016 11:20:29
Is the centrifugal force active in all rotations, from electron to galaxy rotation?
Title: Re: What is centrifugal force?
Post by: rmolnav on 07/10/2016 11:03:56
#35
Yesterday I sent a reply, but it is not here! I don´t know why ...
Not being English my mother tong, it takes me long time to write them! Ill try to repeat it, perhaps rather shorter.
Newton mechanics finds problems at atomic scale (quantum physics should "theoretically" be applied), and at galaxies, where the supposed existence of black holes and dark matter makes the issue very difficult to grasp.
But similarly to the couple Earth/Moon, and Sun/Earth, all satellites rotating around planets, and all planets rotating around stars, don´t move following a straight line thanks to the gravitational pull between them.
When one of the celestial objects is very massive compared to the other, this is the one which is considered to be rotating, and the pull from the other is normally called centripetal. Its reaction, the small one pulling the much bigger, could arguably be called "centrifugal", because its sense is "outward".
What actually happens is that both objects rotate around and axis at their barycenter, usually less than a radio away from the bigger object center.
That is perceived as a wobbling of this last object.
Title: Re: What is centrifugal force?
Post by: rmolnav on 07/10/2016 19:26:29
#36 (continuation)
I said:
"... Its reaction, the small one pulling the much bigger, could arguably be called "centrifugal", because its sense is "outward".
We should keep in mind that use of the term "centrifugal" is not the unique possible one. When dealing with massive objects frequently, for the sake of simplification, their masses are considered to be at their centers of gravity. But they are the addition of huge amounts of particles, that don´t normally experience same forces, equal to the ones in the simplified case of all mass at gravity center.
That fact allows the existence of many, many other pairs of centripetal/centrifugal forces.
Perhaps it would be easier to understand what I mean reading now what I said last year in a post at the subject relative to the existence of two high tides a day instead of one:
"Imaging just a steel cylindrical bar hanging from one of its ends. If we made a horizontal cut, the lower part would fall down. Why it didn´t fall before? Because of internal tensile stresses: the upper side of the section was pulling the lower one, exactly with a force equal to the weight of lower part of the bar.
If we had made the cut a little lower, we could say the same. In this case the weight of lower part would be a little less: just the weight of the slice between the two cuts.
As the slice is not experiencing any acceleration, the sum of all forces applied to is null. The sum of internal stresses it suffers from contiguous material, plus its own weight, has to be null.
If we produced any upward acceleration to the hanging point, internal stresses would increase in such a way that the sum of weight of the slice plus stresses from contiguous material would give a net force that divided by slice mass would be equal to the acceleration"
Title: Re: What is centrifugal force?
Post by: hamdani yusuf on 08/10/2016 04:56:52

According to Newton, a force is required to make an object accelerating. A rotated object by a string is accelerating (towards the center of rotation), hence there must be non-zero force working here, which is centripetal force.
That's why many people don't consider centrifugal force as a real force, at least in Newtonian sense. Because if we include the centrifugal force to the equation of the system, total force would be zero which mean no acceleration, contrary to the observation.
Title: Re: What is centrifugal force?
Post by: jeffreyH on 08/10/2016 09:18:23
Acceleration is a strange beast with two components, direction and magnitude. An unchanging magnitude may well cancel centrifugal and centripetal forces. As in an idealised perfectly circular planetary orbit. Though not in an elliptical orbit.
Title: Re: What is centrifugal force?
Post by: rmolnav on 08/10/2016 12:43:42
#38 and 39
You say:
"...  if we include the centrifugal force to the equation of the system, total force would be zero which mean no acceleration, contrary to the observation" I insist: to reason that way, whoever does it, is erroneous. It is a kind of blunder, in physics and /or maths ...
I thought that in my posts the different objects and acting forces were not "mixed", that I had clearly distinguished which forces are acting on each object.
If you read them carefully, you would understand what I mean.
For instance, in the case of weight and string, basic Physics tell us we must not even consider the addition referred to in what above quoted. The UNIQUE force acting on the weight is the centripetal force (considering the weight as a unit: see#37). An inward pull from the string.
The centripetal force (at that place) is an outward pull, exerted by the weight but FROM THE STRING. That is why, if there were a dynamometer between weight and outer end of string, that centrifugal force would act on dynamometer´s outer side, and forces could be gauged.
 
 
Title: Re: What is centrifugal force?
Post by: rmolnav on 08/10/2016 19:13:35
#40 (continuation)
I had some doubts about which preposition should be used in each case, and I must have put it wrong once at least.
I checked that to pull does´n requires any, but with "a pull" I put "from" in opposite senses. I´ll express now what I meant only with the verb.
- The string pulls inwards the weight (centripetal force).
- As a reaction to that action, the weight pulls outwards the string (centrifugal force).
 To say what quoted " ... include the centrifugal force to the equation of the system , total force would be zero which mean no acceleration...", is erroneous, kind of blunder as I said. At second Newtons law (F=ma), F must be the sum of all forces acting on an object, exerted BY OTHERS ... We can´t add any other force, f.e. one exerted by the considered object on others.
Otherwise we could deduce something utterly absurd: from 2nd and 3rd Newton´s laws it can be deduced that NO object can make (by itself) any other accelerate, because being action and reaction forces equal and opposite, to add both gives zero force ...
Title: Re: What is centrifugal force?
Post by: rmolnav on 09/10/2016 12:53:23
#27:
"The force is MV^2/R where the rotational velocity is around 1000 miles per hour and the distance to the center of the Earth is around 4000 miles. So I guess this is small".
"Small", and "big", are rather meaningless terms, if not specified what compared to.
That could be considered small compared to normal gravitational force, the weight of objects.
But its result is enormous ... Due to that centrifugal force, the equator diameter is app. 43 km bigger than the distance between poles.
That is a kind of permanent high tide all around the equator, with low tides at poles, in the order of 10,000 times highest lunar/solar tides.
And, compared to something also very big, between 2 and 3 times mont Everest (!!)
Title: Re: What is centrifugal force?
Post by: rmolnav on 09/10/2016 13:38:57
#42 (continuation)
Sorry, "only" in the order of  1,000 times, instead of 10,000 !!
Title: Re: What is centrifugal force?
Post by: rmolnav on 10/10/2016 12:30:54
Over last week I tried to convey the main ideas of my stand on the subject. Modestly, I must say I feel pretty sure about this matter, since in last century sixties I studied Solid and Fluid Mechanics for my degree. And many other phenomena related to the subject I later learnt confirmed what initially studied. And I feel I must pass that information to anybody interested.
But I´m not sure about the success of my effort. Very few replies, and rather negative ...
To whoever is really interested in the subject: please read carefully my key posts: 28, 36 and 37.
Any doubt, or opposite view, please kindly tell me.
I still have to complete the application of those ideas to the real and most frequent case of a rotation due to gravity, without any string or similar tool.
But I´ll do it another day/days, most probably in more than one step.
Now, as a kind of divertimento, I´ll bring up a "funny" case, an experiment that anybody can do at home.
Take a cylindrical bucket, or something similar (with vertical inner side). Fill it with water (app. 2/3 of its hight), and put it on the center of a revolving chair. Make it revolve.
Initially flat and horizontal water level will change to a lower level at the center, and the more distant from the center, the higher the water level.  Kind of low tide at center and high tide near the bucket inner surface. Why?
Any comment would be welcome.
Title: Re: What is centrifugal force?
Post by: alancalverd on 10/10/2016 13:16:50

Take a cylindrical bucket, or something similar (with vertical inner side). Fill it with water (app. 2/3 of its hight), and put it on the center of a revolving chair. Make it revolve.
Initially flat and horizontal water level will change to a lower level at the center, and the more distant from the center, the higher the water level.  Kind of low tide at center and high tide near the bucket inner surface. Why?


Centrifugal force.
Title: Re: What is centrifugal force?
Post by: rmolnav on 10/10/2016 19:18:34
#45 Alancalverd
Certainly ... And thank you. But I do expect comments from people who, both here and on:
http://www.thenakedscientists.com/forum/index.php?topic=49715.50,
have said bizarre things  considering that "centrifugal force" should be a kind of forbidden expression, that it isn´t actually a real force ...
There is a big confusion about this subject out there. Even between some scientists (!!).
I´m seeing you are very active on many subjects, but not on either of the two mentioned.
Perhaps you have not seen what I´m referring to. Otherwise you would have sent several refuting replies ...
Title: Re: What is centrifugal force?
Post by: rmolnav on 11/10/2016 12:13:08
#46 (continuation)
After talking about "bizarre things" that some people say, I want to express my greatest respect on everybody, especially on laymen who heard erroneous things said by presumably well educated people.
Before I sent my first post to linked site (#20), I had read some posts which I found utterly wrong. And I started:
“1) Centrifugal” force is NOT a forbidden word whatsoever: it is just a poorly understood and poorly explained force..."
And I carried on unfolding my stand on the subject. Not only on that post, but later on many others.
Many weird things can be seen there, due to the "huge" effort some people had to make trying to explain sea tides (especially the high tide opposite to Moon) without taking into account any centrifugal force, not even mentioning the "forbidden" word.
As far as I can remember, the "leader" was a rather extensive mathematical "contraption" somebody linked:
http://www.newenglandphysics.org/Science_Literature/Journal_Articles/schutz_tides.pdf
Perhaps I should be more humble, and think I could be the wrong one ... After all, I can´t actually fully understand the maths there ...
But I must say I feel pretty sure tides are due to all acting forces, mainly water own weight, lunar (and solar) attraction, and centrifugal forces. Also local conditions, due to the fact that water is not completely free to respond to mentioned forces.
Title: Re: What is centrifugal force?
Post by: rmolnav on 12/10/2016 12:41:13
I must also say I understand how careful some people are when dealing with our topic. In the extreme opposite to what mentioned on #47, there are educated people which consider centrifugal force as if it were a kind of "free for all" force, something we could even take energetic advantage from. That the problem would only be technological, and a lot of money is being spent trying to develop the idea.
And, watch out! Being centrifugal force a reaction f., it exists as long as the centripetal one does. This last one is necessary just to keep the object rotating, and there is nowhere we could take energy from whatsoever. And then, some people go to the #47 extreme !!
F. e., we can throw a stone with a sling. And, with no friction from air and far from Earth (no gravity), instead of throwing it, the stone could even carry on rotating for ever ... But it would be utterly absurd to think of using either of those two opposite forces for something else. The stone would change its trajectory, and the system would collapse.
You can google "space elevator" ...
As I said yesterday, perhaps I should be more humble and accept the possibility of being wrong. There are even several american universities trying to develop the idea. But, with all my respect for the people who are working hard on that idea, sorry, I found it absurd from its initial physical base.
Title: Re: What is centrifugal force?
Post by: hamdani yusuf on 13/10/2016 05:40:48
#40 (continuation)
I had some doubts about which preposition should be used in each case, and I must have put it wrong once at least.
I checked that to pull does´n requires any, but with "a pull" I put "from" in opposite senses. I´ll express now what I meant only with the verb.
- The string pulls inwards the weight (centripetal force).
- As a reaction to that action, the weight pulls outwards the string (centrifugal force).
 To say what quoted " ... include the centrifugal force to the equation of the system , total force would be zero which mean no acceleration...", is erroneous, kind of blunder as I said. At second Newtons law (F=ma), F must be the sum of all forces acting on an object, exerted BY OTHERS ... We can´t add any other force, f.e. one exerted by the considered object on others.
Otherwise we could deduce something utterly absurd: from 2nd and 3rd Newton´s laws it can be deduced that NO object can make (by itself) any other accelerate, because being action and reaction forces equal and opposite, to add both gives zero force ...
How to determine wether a force would produce acceleration?
(https://upload.wikimedia.org/wikipedia/commons/9/97/Centripetal_force.PNG)
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.physicsclassroom.com%2FClass%2Fcircles%2Fu6l4b3.gif&hash=ef1be57e72bf2010450712bcbf622e7f)
Where is the centrifugal force in the first and second picture above?
Title: Re: What is centrifugal force?
Post by: nilak on 13/10/2016 06:57:50
I've made a computer simulation program in which if you select 2 particles with a certain mass and tie them together with a spring, they can rotate around each other without adding the centrifugal force into the motion equations. I only use F=ma; F=kx; dv=a*dt; dx=v*dt; The same happens if you substitute the spring with a gravitational force F=Gm1m2/r^2. So the centrifugal force is the effect of inertia when changing direction. When motion is restricted on a circle, the force of inertia is produced at every little change in the initial direction. This force can be calculated. If your motion is restricted by a different shape (elipse) it will have different formula ( you need to include an angle). Centrifugal force is not a fundamental force, it is only a formula to use for motion restricted on a circle.
Title: Re: What is centrifugal force?
Post by: rmolnav on 13/10/2016 18:37:39
#49 hamdani yusuf
That question has already been dealt with by me (mainly on #28, 36 and 37).
In the first place, we should keep in mind that “centrifugal forces” show up in DIFFERENT fashions ...
Those pictures are only mathematical abstractions of the real thing. The central object is supposed to be much more massive than the other, and, for the sake of simplicity, it is supposed to keep stand still. But, unless it mass were infinite, it is imposible for an object to pull another without moving itself at all.
In both cases we have a primary force: the central object pulls the other (centripetal force).
According to 3rd Newton´s principle, outer object also exerts an equal but opposite force on central one: centrifugal force.
In those cases where there is no physical connection (string, rope, chain ...), both forces are gravitational. By the way, we already know that gravity happens in both senses. It couldn´t be otherwise.
And both objects are considered with their masses concentrated on their gravity center. That is also a simplification. Every particle of each object “feels” independently the gravity pull from the other, not necessarily with same “intensity”, as long as distances are actually different. Those different centripetal forces on each particle originate internal stresses between contiguos particles, that (also due to 3rd principle) go in pairs, being half of them centrifugal.
But I have to come back again to that another day, with clarifying examples.
I already did it last year, under the previously mentioned head subject : “Why are there two high tides a day?”.
In cases where there is a physical connection, the centripetal force is also acting on each particle of both objects, and on each section of the “linking” device, from central to outer object. And on all those places the correspondent centrifugal reaction happens too.   


 
Title: Re: What is centrifugal force?
Post by: rmolnav on 13/10/2016 19:35:03
#50 Nilak
You say:
"So the centrifugal force is the effect of inertia when changing direction".
Not bad idea. But, have you realized that, after all, it is a way of expressing (in a particular case) the three Newton´s Principles?
Whatever happens with linear speed of an object, any change of its direction is a velocity vector change, an acceleration. That results in a curve trajectory.
That acceleration requires an acting force (2nd principle), towards the concave side of the curve (by the way, not necessarily a circumference): centripetal acceleration. If that is exerted (whatever the way) by object  A on B, B by INERTIA tries to maintain its own speed (1st principle), and exerts an equal but opposite force on A: (3rd principle).
But, apparently, you mean centrifugal force is "the effect of inertia" on the object that changes direction ... That seems to establish the idea that centrifugal force in a kind of fictitious force, just an "effect" of inertia.
Please kindly read my #50. There you can see I talk about the "infinite" pairs of centripetal/centrifugal forces acting on the particles of any rotating  object (or just with a curve trajectory). That can be considered an "effect" of inertia,  but it is a REAL force, and it doesn´t mean centrifugal force is not  fundamental. 
Title: Re: What is centrifugal force?
Post by: nilak on 14/10/2016 00:45:56
#50 Nilak
You say:
"So the centrifugal force is the effect of inertia when changing direction".
Not bad idea. But, have you realized that, after all, it is a way of expressing (in a particular case) the three Newton´s Principles?
Whatever happens with linear speed of an object, any change of its direction is a velocity vector change, an acceleration. That results in a curve trajectory.
That acceleration requires an acting force (2nd principle), towards the concave side of the curve (by the way, not necessarily a circumference): centripetal acceleration. If that is exerted (whatever the way) by object  A on B, B by INERTIA tries to maintain its own speed (1st principle), and exerts an equal but opposite force on A: (3rd principle).
But, apparently, you mean centrifugal force is "the effect of inertia" on the object that changes direction ... That seems to establish the idea that centrifugal force in a kind of fictitious force, just an "effect" of inertia.
Please kindly read my #50. There you can see I talk about the "infinite" pairs of centripetal/centrifugal forces acting on the particles of any rotating  object (or just with a curve trajectory). That can be considered an "effect" of inertia,  but it is a REAL force, and it doesn´t mean centrifugal force is not  fundamental.
I've just checked the Wikipedia to see what it says about centrifugal force and I understand the same thing I've tried to explain.
Sorry, reply no 50 is mine.
Title: Re: What is centrifugal force?
Post by: hamdani yusuf on 14/10/2016 02:18:42
...
According to 3rd Newton´s principle, outer object also exerts an equal but opposite force on central one: centrifugal force.
...
If both objects have equal mass, e.g. binary stars, where is the centrifugal force?
Title: Re: What is centrifugal force?
Post by: nilak on 14/10/2016 05:25:38
...
According to 3rd Newton´s principle, outer object also exerts an equal but opposite force on central one: centrifugal force.
...
If both objects have equal mass, e.g. binary stars, where is the centrifugal force?
There are two forces here, for each star, pointing away from the centre of rotation. Also two,
gravity forces, equal to each other and to the centrifugal forces, pointing to the centre of rotation. Instead of gravity you can say the spacetime curvature is causing the attraction if you want to be more precise.
Title: Re: What is centrifugal force?
Post by: rmolnav on 14/10/2016 11:40:29
#54 hamdani yusuf
As I said on #51, if you are considering those stars as if all their constituent material were concentrated on their center of gravities, you are right. All action and reaction forces would go towards the center of the twin system.
But that simplification is not what actually happens. Star A material closer to star B, as well as the material of B closer to A, will be pulled by the other star with stronger force than if we consider outer material. Those (NOT EQUAL to each other) centripetal forces are supposed to produce the centripetal acceleration that the rotation requires. But all parts of the stars, due to own gravity, are obliged to rotate at SAME angular speed. Force excess and/or deficit can only be compensated by internal stresses, changes in pressure when gases.
Gases "try" to concentrate either at closest parts of the pair (centripetal force bigger than what necessary for required centripetal acceleration), or at outer parts (centripetal force smaller than what required). If you consider a traverse "slice" at those outer parts, pressure at outer side will be smaller than at inner side (comparing with pressures if they were not rotating). The net force acting on the slice would be CENTRIFUGAL (apart from own gravity force or weight)
By the way, that is also a good picture of the two high tides on Earth: one at Moon side, and the other at opposite side. Whatever the actual material, phenomena are very similar

 
 
 
Title: Re: What is centrifugal force?
Post by: rmolnav on 14/10/2016 18:02:02
Yesterday I happened to run into Einstein … and I think he “told" me that, at least on one of my key ideas, I´m right.
Do NOT worry! I am not going to talk about relativity theory. Our discussion about centrifugal force, and gravity, must continue within Newton´s Physics.
You can see on #37 the case of a bar hanging from one of its extremes, and the different stresses on each of its sections.
My plan was to pass from that rectilinear situation to a rotational one: the bar, in the space without gravity, somehow rotating around an imaginary hinge at one of its extremes. I haven´t done it yet because I preferred to comment other posts.
It would be very, very similar to the vertical hanging bar case. Each part of the bar would “feel” the centrifugal force in a way quite similar to the effect of the bar weight when hanging vertically. The centripetal acceleration implies an effect on the bar equivalent to a kind of outward, radial weight.
And, a real coincidence, yesterday afternoon tve2 (Spain) emitted “Inside Einstein´s Mind”.
There I learnt that when he was young, and “ruminating” about gravity (before any relativity idea), he imagined something almost exactly equal to what above exposed.
When announcing the video, they said it was from NOVA. From previous cases I know they have plenty of videos on their web site, and I found it:
http://www.pbs.org/wgbh/nova/physics/inside-einsteins-mind.html
Here in Spain is not possible to watch those videos, unless paying for them ...
Approximately at 1/3 of the video, there is a scene with a huge square box, with open front side, and a man “floating” inside (as without gravity). Then he falls onto the box floor, and a little later the point of observation goes back, and we can see Earth globe supporting the box. And afterwards, again at a no gravity place, they lift the box with “g” acceleration.
They say it was imagined by Einstein, who thought the man would feel “floating” or falling down, but, when standing on its feet, he couldn´t tell apart the situations when attracted by Earth´s gravity and when no gravity but the box was being accelerated upwards with “g”.
Its conclusion was that gravity and acceleration must be the “same" thing … And that helped him continue his ideas of space-time deformation, and rest of stuff.
Subsequently, I say, centripetal force/acceleration acts on the rotating object as Einstein´s box lifting force, and makes the object “feel” a centrifugal force, exactly as the man on the box floor feels either his weight (no acceleration) or the acceleration (no weight). And, in other cases (f.e. a child on a swing), both forces added up. 



 
 
 
Title: Re: What is centrifugal force?
Post by: rmolnav on 14/10/2016 18:14:19
By the way, as far as I can remember the word "inertia" doesn´t appear ... (?)
Another day I have to send a post about that example of the child on the swing. And another to say something more about the revolving bucket with water ...
And sorry for my rather poor English (after sending the post I´ve seen I say "its conclusion" referring to Einstein´s !!)
Title: Re: What is centrifugal force?
Post by: rmolnav on 15/10/2016 11:10:25
The case of a child on a swing can be simplified as a pendulum.
There is a difference, as long as in the pendulum case the weight is supposed to be hanging from a string knot (the string pulls the weight), but the swing seat is actually pushing upwards the child. That changes the actual field of reaction forces within child´s body, compared to if he were hanging from his hands.
Another day we can talk about the real case of the swing. Today I propose the simplified pendulum example:
Oscillating_pendulum.gif
Any comments)
Title: Re: What is centrifugal force?
Post by: rmolnav on 16/10/2016 12:10:44
Pendulum I
It seems simple, but there are small but important details that, if not being careful, one can misinterpret facts, or at least confuse others …
That´s why I am now going to consider only the scenario statically (and step by step), without any movement: fixed hanging point, string and weight (I´ll call it W), all in a straight vertical line.
- a) Primary acting force: Earth pulls downwards W.
- b) W does not move. According to 2nd Newton´s principle, the sum of all forces acting on W has to be null.
- c) The unique object that can exert another force on W is the string: it must somehow pull W, with equal but opposite force (watch out: those two opposite forces are not action/reaction forces (3rd principle); they are acting on a unique object, and 3rd principle is about two objects exerting a force on each other).
- d) If the string pulls upwards W, applying now 3rd principle to that pair of objects, we can deduce that W must be pulling downwards the string lower extreme.
- e) That force seems to be a centrifugal one (and centripetal the one mentioned on - c)), but we should keep in mind that if there is no rotatory movement at all, a proper “center” does not actually exist.
- f) And when with movement, we have also to be careful with the term “centripetal force”, because it usually refers to the the radial component of adding up all forces acting on W,  which divided by the mass would give us the “centripetal acceleration” that makes W not to follow a rectilinear trajectory. And in many cases some of those added forces may be in the sense of the “center”, but compensated by others and not producing any acceleration by themselves.
 
Title: Re: What is centrifugal force?
Post by: hamdani yusuf on 17/10/2016 04:29:08
Pendulum I
It seems simple, but there are small but important details that, if not being careful, one can misinterpret facts, or at least confuse others …
That´s why I am now going to consider only the scenario statically (and step by step), without any movement: fixed hanging point, string and weight (I´ll call it W), all in a straight vertical line.
- a) Primary acting force: Earth pulls downwards W.
- b) W does not move. According to 2nd Newton´s principle, the sum of all forces acting on W has to be null.
- c) The unique object that can exert another force on W is the string: it must somehow pull W, with equal but opposite force (watch out: those two opposite forces are not action/reaction forces (3rd principle); they are acting on a unique object, and 3rd principle is about two objects exerting a force on each other).
- d) If the string pulls upwards W, applying now 3rd principle to that pair of objects, we can deduce that W must be pulling downwards the string lower extreme.
- e) That force seems to be a centrifugal one (and centripetal the one mentioned on - c)), but we should keep in mind that if there is no rotatory movement at all, a proper “center” does not actually exist.
- f) And when with movement, we have also to be careful with the term “centripetal force”, because it usually refers to the the radial component of adding up all forces acting on W,  which divided by the mass would give us the “centripetal acceleration” that makes W not to follow a rectilinear trajectory. And in many cases some of those added forces may be in the sense of the “center”, but compensated by others and not producing any acceleration by themselves.
I think your examples above don't clear things up, but rather confusing.
Title: Re: What is centrifugal force?
Post by: rmolnav on 17/10/2016 11:45:46
#61 hamdani yusuf
"I think your examples above don't clear things up, but rather confusing".
There are not "examples", it is only a rather simple case, analyzed step by step.
Could you please specify which concrete step and/or point you find confusing?
My aim there was that, reading later posts of mine including pendulum oscillation, nobody would erroneously think again (f.e.) similarly to what reflected on your own #38:
"Because if we include the centrifugal force to the equation of the system, total force would be zero which mean no acceleration, contrary to the observation”,
what was later dealt with by me on #39 and 40. I expected it was already clear to you ...
I consider what said on #60, if each paragraph is (one by one) read carefully, should be understood with no difficulty.
I understand they could seem rather far fetched details.
But I´m convinced that, not to have them clearly understood by many people, is the main reason why there is such a big confusion about the subject out there.
Title: Re: What is centrifugal force?
Post by: hamdani yusuf on 17/10/2016 12:08:46
#61 hamdani yusuf
"I think your examples above don't clear things up, but rather confusing".
There are not "examples", it is only a rather simple case, analyzed step by step.
Could you please specify which concrete step and/or point you find confusing?
My aim there was that, reading later posts of mine including pendulum oscillation, nobody would erroneously think again (f.e.) similarly to what reflected on your own #38:
"Because if we include the centrifugal force to the equation of the system, total force would be zero which mean no acceleration, contrary to the observation”,
what was later dealt with by me on #39 and 40. I expected it was already clear to you ...
I consider what said on #60, if each paragraph is (one by one) read carefully, should be understood with no difficulty.
I understand they could seem rather far fetched details.
But I´m convinced that, not to have them clearly understood by many people, is the main reason why there is such a big confusion about the subject out there.
When trying to explain centripetal and centrifugal forces, we should focus more on the generation of force due to circular movement of an object. Don't complicate things with additional forces whose direction is not radial.
In the case of astronauts in ISS, do they experience centrifugal force? Does it have the same magnitude as the centripetal force by earth gravity which keeps them in orbit?
Title: Re: What is centrifugal force?
Post by: rmolnav on 17/10/2016 19:29:17
#63 hamdani yusuf
« on: Today at 04:29:08 » Quote (selected):
"Don't complicate things with additional forces whose direction is not radial".
Certainly, we should not complicate things with any unnecessary stuff ... But please note that a pendulum oscilates because of the action of the very existence of a tangential component of its weight, which produces a tangential acceleration.
My concrete aim was nobody would mix them later when analyzing the oscillation, that is a kind of partial rotation, but with variable speed.
And you also ask:
"In the case of astronauts in ISS, do they experience centrifugal force? Does it have the same magnitude as the centripetal force by earth gravity which keeps them in orbit?"
In that scenario there are also subtleties one has to take into account carefully.
Considering the mass of an astronaut as a hole, 3rd Newton´s principle tell us that, if earth gravity pulls him down, he also pulls earth upwards.
But that pull is negligible to earth.
As a unit, the astronaut only experiences centripetal force, which makes him rotate.
But his body parts and members, if he were much, much taller, would differently experience earth gravity, especially when in  "vertical"  (radial) position.
Why? Because the distance from his head to earth would be greater than that distance from his feet ...
Besides that, the trajectories of those two body parts would be slightly different circumferences ... For a unique angular speed of rotation, that would mean his feet would require a smaller centripetal force than what corresponds to experienced gravity, and the opposite at his head.
Internal stresses/forces would happen to compensate those differences. And internal stress/forces go in pairs, due to 3rd Newton´s principle.
Half of them would be centripetal, and half centrifugal.
That seems bizarre, because distance differences are relatively negligible. But if ISS were much, much bigger in radial sense, other analogous effects would happen there, and be sure they should be taken into consideration. 
 
 
Title: Re: What is centrifugal force?
Post by: hamdani yusuf on 18/10/2016 02:25:34
...
"In the case of astronauts in ISS, do they experience centrifugal force? Does it have the same magnitude as the centripetal force by earth gravity which keeps them in orbit?"
In that scenario there are also subtleties one has to take into account carefully.
Considering the mass of an astronaut as a hole, 3rd Newton´s principle tell us that, if earth gravity pulls him down, he also pulls earth upwards.
...
The pulling of the earth is also centripetal, toward the barycenter of the system. Hence there is no apparent centrifugal force here.
Title: Re: What is centrifugal force?
Post by: puppypower on 18/10/2016 12:19:54
The centrifugal force appears when linear momentum, meets angular momentum, and two merge into angular momentum, while remaining separate and distinct. If we break the merger, the distinction will reappear.
Title: Re: What is centrifugal force?
Post by: rmolnav on 18/10/2016 12:37:49
#65 hamdani yusuf
Please note the expression “centrifugal force” does NOT appear in what quoted by you. Not even the term “reaction force” …
3rd principle affects to any object exerting a force on another, and viceversa. But not always is easy to say which is action and which reaction. I have seen it is better not to introduce that issue in my expositions.
Let me transform a little the astronaut case.
Let us imagine he goes out of ISS, to a position keeping the orbit but many meters after the station.
There would be what we can call a dynamic equilibrium: earth pulls the man, but he does not move downwards because there gravity acceleration is exactly equal to the square of his tangential speed divided by the radius of his orbit. Velocity vector only changes direction, and that lets him rotate, as when inside the station.
Surely he would have gone out of ISS with a safety “rope”, let us suppose with a knot around one of his wrists. If another astronaut inside the station tights the rope and strongly pulls him, the dynamic equilibrium ends: that pull increases his tangential velocity. And if we divide gravity attraction by his mass, we get an acceleration smaller than what required to keep him in that orbit (the square of the actual speed divided by the radius) …
The astronaut would move not only tangentially, but also radially, upwards. Then the rope pull would have a downward component. That “centripetal” component of the rope pull, according to 3rd principle would mean our man would also pull the rope, upwards: a CENTRIFUGAL force.
Besides, within the astronaut body, there would be stresses (wrist and forearm would be pulling rest of the body … 3rd principle would also apply there ...
Somebody could say: rather confusing example … Or: well, that is a particular case, with more than two objects (earth, ISS, rope and astronaut).
But in ALL real cases there are many, many more “objects” to be considered, because their different parts (whatever their size) experience gravity attraction from other massive objects independently …
Nature is much more complex than most mathematical simplifications ...
Title: Re: What is centrifugal force?
Post by: hamdani yusuf on 18/10/2016 18:22:14
#65 hamdani yusuf
Please note the expression “centrifugal force” does NOT appear in what quoted by you. Not even the term “reaction force” …
3rd principle affects to any object exerting a force on another, and viceversa. But not always is easy to say which is action and which reaction. I have seen it is better not to introduce that issue in my expositions.
Let me transform a little the astronaut case.
Let us imagine he goes out of ISS, to a position keeping the orbit but many meters after the station.
There would be what we can call a dynamic equilibrium: earth pulls the man, but he does not move downwards because there gravity acceleration is exactly equal to the square of his tangential speed divided by the radius of his orbit. Velocity vector only changes direction, and that lets him rotate, as when inside the station.
Surely he would have gone out of ISS with a safety “rope”, let us suppose with a knot around one of his wrists. If another astronaut inside the station tights the rope and strongly pulls him, the dynamic equilibrium ends: that pull increases his tangential velocity. And if we divide gravity attraction by his mass, we get an acceleration smaller than what required to keep him in that orbit (the square of the actual speed divided by the radius) …
The astronaut would move not only tangentially, but also radially, upwards. Then the rope pull would have a downward component. That “centripetal” component of the rope pull, according to 3rd principle would mean our man would also pull the rope, upwards: a CENTRIFUGAL force.
Besides, within the astronaut body, there would be stresses (wrist and forearm would be pulling rest of the body … 3rd principle would also apply there ...
Somebody could say: rather confusing example … Or: well, that is a particular case, with more than two objects (earth, ISS, rope and astronaut).
But in ALL real cases there are many, many more “objects” to be considered, because their different parts (whatever their size) experience gravity attraction from other massive objects independently …
Nature is much more complex than most mathematical simplifications ...
Why in ISS centrifugal force doesn't seem to be equal to centripetal force?
Title: Re: What is centrifugal force?
Post by: rmolnav on 18/10/2016 19:48:35
#68 hamdani yusuf
I think I´ve already answered similar questions.
If ISS were considered a single object, with all its mass concentrated in its center of gravity, NO centrifugal force would occur there: it only would be interacting with earth, pulling it back with a force equal to the centripetal force required for ISS´s actual speed of rotation at that distance.
But, as ISS has a size, particulary its radial hight, some of its parts are further from earth than others ... Gravity is not EXACTILY the same all through its hight. But all of them rotate at same speed. That produces an actual centripetal force "surplus" at its lower parts, and a "deficit" at upper parts.
That has to be compensated by mean of a field of internal stresses/forces, in pairs to satisfy 3rd Newton´s principle.
Half of them go downwards, and the other half upwards, which can be called CENTRIFUGAL.
Those forces would make ISS stretch in radial sense, the same that happens with ALL cosmic objects rotating around their barycenter.
Certainly, those effects at ISS must be almost negligible, but not completely. Haven´t you realized how  vertically small ISS is? Surely it is so to further minimize those effects.
Title: Re: What is centrifugal force?
Post by: hamdani yusuf on 19/10/2016 02:40:56
Quote
In Newtonian mechanics, the centrifugal force is an inertial force (also called a 'fictitious' or 'pseudo' force) directed away from the axis of rotation that appears to act on all objects when viewed in a rotating reference frame.

The term has historically sometimes also been used to refer to the reaction force to a centripetal force.

The centrifugal force is an outward force apparent in a rotating reference frame; it does not exist when measurements are made in an inertial frame of reference.
That's what wikipedia said.
Title: Re: What is centrifugal force?
Post by: rmolnav on 19/10/2016 12:17:19
#70
Wikipedia is not always completely right. Even it has errors.
Last year I already said:
“I know centrifugal force can be considered as an inertial, actually kind of ficticious force … But not only that way”.
(#28 of  http://www.thenakedscientists.com/forum/index.php?topic=49715.25 ).
Besides, what quoted by you is self-contradictory, because they also say:
"The term has historically sometimes also been used to refer to the reaction force to a centripetal force",
and all my examples are based on that fact. They say just "sometimes", but in all my examples that term has been used because pairs of centripetal forces and their reactions were present ... How do you think we should call a force opposite to a centripetal one?

 

 
Title: Re: What is centrifugal force?
Post by: rmolnav on 19/10/2016 19:13:34
#70 (continuation)
Rather than being self-contradictory, Wikipedia article author seems to consider that centrifugal f. actually is the ficticious f. he refers to, that to use the expression for the reaction to the centripetal f. is a kind of exceptional use …
I do consider it would rather be the opposite. His field must be Theoretical Physics or Maths, and he refers to a “trick” for when an inertial frame of reference: the use of a fictitious force, equal but opposite to centripetal f., but both forces applied on SAME unique object.
But the other case refers to a REAL force, which has been acting in the Universe since several billion years ago, since first pair of rotating stars appeared. Since then, hose forces and centripetal ones, together with own gravity of considered cosmic objects, have been deforming, and even broking apart, many of those objects:
"The limiting distance to which a satellite can approach without breaking up depends on the rigidity of the satellite. At one extreme, a completely rigid satellite will maintain its shape until tidal forces break it apart. At the other extreme, a highly fluid satellite gradually deforms leading to increased tidal forces, causing the satellite to elongate, further compounding the tidal forces and causing it to break apart more readily ..."
https://en.wikipedia.org/wiki/Roche_limit
Title: Re: What is centrifugal force?
Post by: hamdani yusuf on 19/10/2016 23:15:53
... How do you think we should call a force opposite to a centripetal one?
It could also be centripetal force. See binary stars.

Centrifugal force is considered pseudo/fictitious because it does not exist when measurements are made in an inertial frame of reference.
Title: Re: What is centrifugal force?
Post by: rmolnav on 20/10/2016 11:12:34
#73
Please kindly see #56, were your #54, with two identical binary stars case, was already dealt with.
AT BOTH OUTER PARTS of the pair, gas pressure decreases, and bulges appear, for same reason as our equator diameter is bigger than pole to pole distance: CENTRIFUGAL forces experienced by ANY molecule whose distance to the other star C.G is bigger than the distance between the two C.G.
You seem unable to distinguish the simplified case when considering all star masses concentrated on their respective C.G. (a rather theoretical trick), from REAL cases, in which each molecule actually "feels" gravity (from rest of massive objects) independently.
And 3rd Newton´s principle also applies to ALL those "infinite" tiny forces, and to internal stresses that happen throughout all objects. 
Title: Re: What is centrifugal force?
Post by: rmolnav on 20/10/2016 11:19:56
#72 (continuation)
"Jupiter – the most massive planet in the Solar System – causes the Sun to move at roughly 35km/h”
(both actually rotate around the barycenter axis of the pair, very near to Sun´s C. G.  - apart from other much smaller wobblings due to rest of planets)
"… When the star moves towards or away from you, the wavelength of its light shortens or lengthens, respectively".
http://www.bbc.com/earth/story/20161019-the-first-planet-around-another-star
Title: Re: What is centrifugal force?
Post by: hamdani yusuf on 20/10/2016 13:28:38
#73
Please kindly see #56, were your #54, with two identical binary stars case, was already dealt with.
AT BOTH OUTER PARTS of the pair, gas pressure decreases, and bulges appear, for same reason as our equator diameter is bigger than pole to pole distance: CENTRIFUGAL forces experienced by ANY molecule whose distance to the other star C.G is bigger than the distance between the two C.G.
You seem unable to distinguish the simplified case when considering all star masses concentrated on their respective C.G. (a rather theoretical trick), from REAL cases, in which each molecule actually "feels" gravity (from rest of massive objects) independently.
And 3rd Newton´s principle also applies to ALL those "infinite" tiny forces, and to internal stresses that happen throughout all objects.
There is alternative name for the cause of those bulges : inhomogeneity of centripetal forces among the molecules making up the stars.
Title: Re: What is centrifugal force?
Post by: hamdani yusuf on 20/10/2016 13:31:39
May I know your objection to wikipedia's statement that
Centrifugal force is considered pseudo/fictitious because it does not exist when measurements are made in an inertial frame of reference?
Title: Re: What is centrifugal force?
Post by: rmolnav on 20/10/2016 18:46:03
#77 hamdani yusuf
I have no objection to that statement whatsoever, if THAT is the case: "when measurements are made in an inertial frame of reference".
But in most real cases the frame of reference has NOT to be necessarily an inertial one.
Besides, forces do exist in nature, centrifugal ones included, long, long before anybody could make measurements ... 
Title: Re: What is centrifugal force?
Post by: rmolnav on 22/10/2016 11:35:33
REVOLVING WATER BUCKET
On #44 I brought up this case and asked for possible reasons of water surface change.
There was only an answer, from Alancalverd, “centrifugal force”.
I consider it could be very clarifying to analyze what happens in detail (aiming even laymen could understand) , especially because it is an example of in how different ways matter actually can respond to acting forces: gravitational, centripetal, centrifugal (or whatever we could call them,  “outward inertial forces”? ). As I´ve already said, they produce internal stresses and/or deformations, in different fashions depending on each case.
What causes the water rotate is inner bucket surface rotation, thanks to friction …  Outer water molecule inertia tries to keep constant (tangential) speed vectors. The bucket makes it impossible, kind of PUSH (not "pull" as in other cases we´ve previously seen) inwards the water (centripetal force), and water rotates.
That (forces and movement) is transmitted inwards up to the axis of rotation.
All those transmitted centripetal forces have their “mirror” forces (3rd Newton´s principle), centrifugal ones.
One could ask himself: ok, but if all rotations are on horizontal plans, and centripetal and centrifugal (and friction) forces are also horizontal, why outer water rises (the bigger the radius, the higher the water level)?
If instead of water there were solid stuff (f.e., concrete), only internal (mainly compression) forces would occur. But liquids respond with an increase of what is usually called hydraulic pressure, which acts in ALL directions.
In any point pressure must also be equal to the weight of a 1 cm2 section column of water, from the point up to water surface.
That makes water surface acquire its concave shape. It is a kind of dynamic equilibrium, result of ALL acting forces.







 
 
 
Title: Re: What is centrifugal force?
Post by: rmolnav on 22/10/2016 12:02:31
#79 (continuation)
When mentioning concrete instead of water, as I was thinking of bucket inward pushing the water, I said  there would be mainly compression internal forces (within concrete)
It would be correct if the change were only concrete instead of water, maintaining the bucket.
If there were no bucket, tensile internal stresses would occur instead (by the way, also a clear prove of centrifugal force reality)
Title: Re: What is centrifugal force?
Post by: jeffreyH on 22/10/2016 12:14:37
The main problem with the idea of centrifugal force is that the vector tangent to the rotation is producing the outward 'force'. So that if a bucket on the end of a rope stops being confined, the rope is released, it does not move away in the radial direction. If the bucket were on a bungee rope then the experiment would be more interesting. As the speed of rotation increases how does the rope react?
Title: Re: What is centrifugal force?
Post by: rmolnav on 22/10/2016 13:00:48
#81 jeffreyH
If you talk about a bucket following my later posts, please note the case I previously brought up was a bucket on top of a REVOLVING chair ...
(by the way, as a continuation to #80: the bucket with concrete should be a metallic one; if plastic it could barely withstand concrete outward forces ...)
Your case is different. You say :
"The main problem with the idea of centrifugal force is that the vector tangent to the rotation is producing the outward 'force'"
SORRY, but I find that utterly erroneous. You are mixing a "vector tangent to the rotation", which is a VELOCITY vector, and a FORCE (outward, centrifugal, whatever we may call it).
To put it as simple as possible:
1) To CHANGE de direction of that velocity, a centripetal force is required (1st Newton´s principle).
2) In your case, that force is the one caused by the rope, that pulls the bucket (inwards)
3) According to 3rd Newton´s principle, the bucket also pulls the rope (outward, or centrifugal force).
If it were with a bungee rope, the tension would make it elongate, until reaching an equilibrium. The same that happened to the spring of a dynamometer between rope and bucket, case we already dealt with in previous posts ... I suppose you didn´t read them.
 
Title: Re: What is centrifugal force?
Post by: hamdani yusuf on 23/10/2016 10:56:27
In inertial reference frame, water in rotating bucket is experiencing centripetal force done by the bucket's wall. Outer part of water molecules which are directly in contact with the wall then push inner part. Water molecules located in the rotation axis don't experient this force.
Title: Re: What is centrifugal force?
Post by: rmolnav on 23/10/2016 12:01:25
#83 hamdani yusuf

Certainly … But I would say that happens whatever the reference frame.
And an inward push (similar to that by bucket inner surface >> contiguous water molecules) is also exerted by each cylindrical layer of water on contiguous inner layer, decreasing in intensity up to the axis of rotation, where water speed keeps null, and no centripetal acceleration is needed to change a constant velocity vector.
And, according to 3rd Newton´s principle, EVERY cylindrical layer of water pushed by outer one, pushes back this contiguous outer layer (outwards) … A real field of CENTRIFUGAL forces …
That´s why water pressure increases from axis to bucket inner surface (at same hight), what changes water surface shape.
Title: Re: What is centrifugal force?
Post by: rmolnav on 24/10/2016 11:34:53
#84 (continuation)
Logically, there is a similitud between the revolving water bucket and our planet surface deformation due to its daily revolution.
At the equator, and decreasingly at higher latitudes, ocean water also "feels" centrifugal forces as in the revolving bucket, but their field of vectors is different due to not having a solid barrier as bucket inner surface.
On our planet what makes water not to follow tangential straight lines is the very earth gravity. More precisely, components of local weight vectors perpendicular to North-South axis of rotation.
The further from equator, the smaller tangential velocities. Centripetal force vectors and  local gravity vectors (weights) ad up, and water surface reaches an equilibrium shape, with water "level" increasing from poles to equator.
Within the bucket a similar deformation is not possible, and what increases (from axis to bucket inner surface) is water hight (and decreases closer to revolving axis, because water cannot expand)
Title: Re: What is centrifugal force?
Post by: rmolnav on 24/10/2016 12:19:34
#85 (continuation)
After sending recent post, I´ve seen that now is me who writes something rather erroneous:
" Centripetal force vectors and  local gravity vectors (weights) ad up".
Centripetal accelerations required for the rotation of water are actually due to more forces, weight included.
In each latitud plan, centripetal forces have their mirror outward forces (as exposed in the bucket case), which are centrifugal.
The result of ALL forces exerted on each water particle (own weight, and pressure forces from contiguous particles - inward and outward forces included), divided by the particle mass, must be the required centripetal acceleration necessary for the particle circular movement.
And the equilibrium is reached, as we know, with a shape surface not completely spherical, with equator diameter bigger than N-S poles distance.
 
Title: Re: What is centrifugal force?
Post by: hamdani yusuf on 24/10/2016 18:02:20
in rotating water bucket, the shape of water surface is paraboloid. Similar technique has been used to form mirrors for telescope.
Title: Re: What is centrifugal force?
Post by: rmolnav on 24/10/2016 19:06:58
#87 hamdani yusuf

Right. But ...
I already commented that nature is far more complex than most simplifications we make, which aim to get results accurate enough for our needs.
In the case we are discussing, the paraboloid is not perfect, and we only get it after some time of stabilization.
As friction is what makes water rotate, that is inwards transmitted from inner bucket surface up to the axis of revolution. And friction is not 100% effective at "pulling tangentially" inner cylindrical layers of water, as there is always some loss of energy. Especially if instead of water we had a more viscous liquid.
Not considering that, angular speed would be the same across the bucket diameter, and tangential speed would increase from axis to bucket, proportionally to the square of the radius. THAT would cause the paraboloid surface.
But angular speed decreases very slightly from bucket surface to axis of rotation. Much more at initial transient phase, if we started from standing still.
The result is that water hight increases outwards slightly more than in the paraboloid, because centripetal and centrifugal forces do the same, as well as resulting water pressure.
Title: Re: What is centrifugal force?
Post by: hamdani yusuf on 25/10/2016 02:57:22
According to Oliver Darrigol's book that I recently read, Poincare classified source of force as external and inertial forces.
In inertial reference frame, only external force can produce acceleration, such as electromagnetic and gravity, or reduce acceleration like friction.
In Newton's third law, the distinction is ignored. Hence total external force is equal to total inertial force (opposite direction), while the acceleration measured in inertial reference frame only depends on total external force.
Centrifugal force is an inertial type force, analogous with inertial mass in linear acceleration.
For example, a system has two external forces +5 N and -3 N. The mass of the system is 2 kg.
Total external force is 5-3=2 N. Inertial force is equal and opposite to the external force, hence -2N.
The acceleration only depends on the external force, which is 2 N / 2 kg = 1 m/s2.
Title: Re: What is centrifugal force?
Post by: jerrygg38 on 25/10/2016 15:24:55
The centrifugal force 
  The centrifugal force is difficult to understand fully unless we break down the Einsteinian mass into frontal and rearward components. The frontal mass is larger than the rearward mass and the geometric mean is the Einsteinian inertial mass. This means that there is a pull on the Earth from the sun at the center of gravity of the Earth. In addition there is a twist on the Earth because the pull of gravity is stronger on the front of motion than the rear.  The Earth wants to move in a straight line but it is twisted to curve. A space time force counteracts this and this is the centrifugal force.
Title: Re: What is centrifugal force?
Post by: rmolnav on 25/10/2016 19:38:54
#89 hamdani yusuf
I do agree with most of what you say ...
In most of my examples it was clear that, being equal but opposite to each other (3rd N. principle) the forces (if any) exerted between two objects, their total force is always null. And they would not produce any acceleration to the pair, considered as a hole (a system).
But acceleration IS NOT the unique possible effect of a force. So, null acceleration doesn´t necessarily mean lack of forces.
When two o more objects (included the case of different parts of a single object) are somehow "obliged" to move at same speed, if external forces (for any reason) are not distributed proportionally to masses of each object (o part of an object), they originate internal forces which deform the objects, whatever the sum of all external forces.
And if the system is rotating, as I´ve already exposed in many examples, internal forces are basically perpendicular to axis of rotation, and mainly centripetal and centrifugal forces, 50% of each type. And the can make the objects stretch or shrink, and not equally at different parts of the bodies.
By the way, haven´t you realized that usual expressions are centripetal force, centrifugal force, centripetal acceleration ... but NEVER "centrifugal acceleration"?
That is consistent with facts: centrifugal force is something REAL, but can not produce any acceleration ... Precisely because its origine is that "something" is obliging an object to change the direction of its speed (a centripetal force causing a centripetal acceleration), and the reaction of the object (3rd N. principle) is an equal but opposite force, exerted by the object on that "something" ...
Another example: somebody making a sling with a stone rotate ... The centrifugal force only keeps tight the sling (a centripetal force alone wouldn´t be able to do it) ...
Somebody would say: but when the stone is thrown, it goes tangentially, not radially ... Of course !!!. The centrifugal force was not being exerted ON the stone (if considered as whole), it was being exerted BY the stone, but ON the extreme of the swing. As soon as centripetal force ceases, two main things happen:
1) The stone continues with its velocity vector in that moment (acc. to 1st N. principle).
2) The swing is not tight any more, and bends down, also following some rotational movement, due to its own inertia. Only for a short time, as air friction reduces its angular speed.
Title: Re: What is centrifugal force?
Post by: rmolnav on 25/10/2016 19:54:45
#91 (continuation)
Sorry: a couple of times I said "swing", but I meant "sling" ...
Title: Re: What is centrifugal force?
Post by: rmolnav on 26/10/2016 10:09:13
More about the sling case.

As you know, that device is a two part string, with a kind of loop, broader piece joining the two parts at their outer extremes, that supports the stone to be thrown.
In other cases centripetal forces are pulls, but when rotating the sling, mentioned loop piece, as it rounds the stone, actually pushes the stone inwards. And, due to 3rd N. principle, the stone pushes back that loop piece, outwards … Whatever name could be given to that force, it IS centrifugal (“tending" to move away from a centre).

Two pieces of evidence:

Had we put a chewing gum between the stone and the loop piece, it would flatten, due to the fact of being compressed by those opposite forces, on its inner and outer sides.
Were we going to throw a clod instead of a stone, it wouldn´t be possible (unless very softly …), because it would break down, due to internal compression stresses caused by acting centripetal and centrifugal forces.
Title: Re: What is centrifugal force?
Post by: rmolnav on 27/10/2016 19:25:32
#90 jerrygg38
Einstein´s gravity theory is difficult to grasp to me (as to most people, I am afraid). So, on this subject I don´t feel sure enough to discuss. That´s why I have not commented your post last days, preferring to deal with others.
But now it seems we are having a kind of rest, and I´ve decided to say a couple of things.
On the one hand, what you say may be right, but I think last words should be: "and this is a centrifugal force”. I´ve already  shown many cases where we also have centrifugal forces, quite different to your case.
And on the other hand, the deep roots of the forces on my examples (gravity, inertial forces, centrifugal forces) may be, according to Einstein´s theory, "bending" of space-time, or related mass changes ...  But I consider that, at least at speeds so much smaller than light speed, ALL cases where centrifugal force may appear can be explained within Newton´s Physics.
Title: Re: What is centrifugal force?
Post by: jerrygg38 on 28/10/2016 13:45:41
The main problem with the idea of centrifugal force is that the vector tangent to the rotation is producing the outward 'force'. So that if a bucket on the end of a rope stops being confined, the rope is released, it does not move away in the radial direction. If the bucket were on a bungee rope then the experiment would be more interesting. As the speed of rotation increases how does the rope react?
   The vector tangent to the rotation defines the moving gravitational field of the object. The rope pulls the object away from the field. The centrifugal force is caused by the pressure of the object and future gravitational field verses the present gravitational field.
   If you keep increasing the speed the rope will either break or wind up. If it breaks  the object will continue to move in a straight line tangent to the rotation as it follows its present gravitational field.
Title: Re: What is centrifugal force?
Post by: jerrygg38 on 28/10/2016 13:55:46
#90 jerrygg38
Einstein´s gravity theory is difficult to grasp to me (as to most people, I am afraid). So, on this subject I don´t feel sure enough to discuss. That´s why I have not commented your post last days, preferring to deal with others.
But now it seems we are having a kind of rest, and I´ve decided to say a couple of things.
On the one hand, what you say may be right, but I think last words should be: "and this is a centrifugal force”. I´ve already  shown many cases where we also have centrifugal forces, quite different to your case.
And on the other hand, the deep roots of the forces on my examples (gravity, inertial forces, centrifugal forces) may be, according to Einstein´s theory, "bending" of space-time, or related mass changes ...  But I consider that, at least at speeds so much smaller than light speed, ALL cases where centrifugal force may appear can be explained within Newton´s Physics.
  Yes. Newton's physics works quite well to explain most things. I just posed another explanation of the centrifugal force. No curved space time is really necessary. All we have is a moving gravitational force of an object and a force pulling the object toward it. Then we have a present gravitational force vector and a future gravitational force vector. Thus the actual centrifugal force is a small differential vector. No Einsteinian space time is required to understand that.
  To me Einsteinian space time is merely a description of how the gravitational fields work. Space does not curve. Space does not bend. These are strange and false concepts. It is the gravitational fields within space that curves and bends. Einstein is correct in his math but space itself has no properties. It is what exists within space that has the properties.
Title: Re: What is centrifugal force?
Post by: jerrygg38 on 28/10/2016 14:33:23
Rmolnav discussion with hundani yusuf with comments from  Jerrygg 10-28-16
Rmolnaw said : By the way, haven´t you realized that usual expressions are centripetal force, centrifugal force, centripetal acceleration ... but NEVER "centrifugal acceleration"?
That is consistent with facts: centrifugal force is something REAL, but can not produce any acceleration
Jerrygg38: The problem is that every atom has its own gravitational field which moves with the object. When a force such as a strong gravitational field such as the Earth acts upon an object it produces an acceleration. When an object is accelerated by the Earth such as a falling apple there is a counter force of the present field of the apple and  the future field of the apple. Thus an actual force is generated. When an object is spinning on a rope the rope acts like the Earth and the counter forces is caused by the motion of the present field of the object and the future field. I have just been working on the centrifugal force for a month or so as my main concern is the fundamental components of the universe. However why hasn’t anyone considered that everything has its own self gravitational field?
    Rmolnav said: Another example: somebody making a sling with a stone rotate ... The centrifugal force only keeps tight the sling (a centripetal force alone wouldn´t be able to do it) ...
Somebody would say: but when the stone is thrown, it goes tangentially, not radially ... Of course !!!. The centrifugal force was not being exerted ON the stone (if considered as whole), it was being exerted BY the stone, but ON the extreme of the swing. As soon as centripetal force ceases, two main things happen:
1) The stone continues with its velocity vector in that moment (acc. to 1st N. principle).
2) The swing is not tight any more, and bends down, also following some rotational movement, due to its own inertia. Only for a short time, as air friction reduces its angular speed.
Jerrygg38 responded: Yes. The centrifugal force produces a differential pressure from the present moving gravitational field of the stone and the future gravitational field of the stone.
  It is important to understand that every piece of matter has its own little gravitational field. The rock has billions of billions of little gravitational fields. They combine to look like a single gravitational field at the center of gravity of the rock. If you move the rock with velocity V, the present gravitational field will resist the motion. However once the rocks speed is stabilized you have a moving rock with velocity V and a moving gravitational field with velocity V and the force is then zero. Just pure classical physics. Einstein’s physics shows up as the speed increases greatly but it also shows up as the binding energy of the hydrogen atom as the Einsteinian mass increase in the first orbit at C/137 is identical with the binding energy. The same is true of the neutrino which is an Einsteinian mass increase as an electron is crushed into the proton at 0.9186C. Therefore Einstein’s work shows up everywhere.
Title: Re: What is centrifugal force?
Post by: rmolnav on 28/10/2016 19:47:04
#97
"Jerrygg38 responded: Yes. The centrifugal force produces a differential pressure from the present moving gravitational field of the stone and the future gravitational field of the stone”
Perhaps you are right, but I have to say I don´t fully understand what you mean, especially with the concept of “pressure”, and subsequently the idea of a “differential pressure” produced by centrifugal force …
As I said on my last post, I think it would be better we keep our discussion within Newton´s Mechanics. It should be sufficient for us to understand the subject.
If the root “metaphysical” cause of gravity and inertial forces is the curving of space-time due to massive objects … OK. But the EFFECTS of those forces can be explained whatever the deep nature of gravity.
Keep in mind many people seem to have difficulties when trying to understand basic Newton´s Mechanics … let alone Einstein´s theories.
You yourself said several absurd things, on your initial #0, #2, #5, #10, #12, #23 … All those only before I sent my first one (#28), which I saw then, but didn´t deal with separately (precisely this morning I read more carefully #0 to 27 …) , preferring to say "SOME of you base your arguments on the idea that …”
So, let me suggest you to try and grasp before the subject within Newton´s boundaries. After that, if you want to go deeper into actual (at least so considered by modern “theories”) nature of gravity, give it a go, and be lucky ...
Title: Re: What is centrifugal force?
Post by: rmolnav on 29/10/2016 07:24:45
#98 (Continuation)
I must say that, previous to my first post #28, yesterday I also saw that others said things which may show some confusion: puppypower (#11), jeffreyH (#15 and 19), PhysBang (#6 and same ? paragraph than hamdani yusuf on #16 and #38 resp.).
And many later posts have also signs of not completely clear ideas, as I said within Newton´s theory simpler realm.
On the other hand, Alancalverd and PmbPhy seem to have it clear. But they have intervened few times. Perhaps they got “tired” ...
I insist: let us firstly try and grasp the meaning of the issue, and the effects of those forces (gravity, inertial f. …) without Einstein´s Mechanics … Understanding of nature of deeper nature of gravity and inertial forces is not necessary to deal with their effects that we can see, feel, calculate, and measure. Einstein theories are much more difficult to grasp for most of us ...
 
Title: Re: What is centrifugal force?
Post by: EvaWilliams on 29/10/2016 12:13:19
Its a force which attracts the body towards its centre of the circle its opposite force is centrifugal force
Title: Re: What is centrifugal force?
Post by: jerrygg38 on 29/10/2016 13:50:36
Centrifugal force 10-29-16
Rmolnav said:
So, let me suggest you to try and grasp before the subject within Newton´s boundaries. After that, if you want to go deeper into actual (at least so considered by modern “theories”) nature of gravity, give it a go, and be lucky ...Jerrygg replied.
   Modern physics attempts to explain why gravity works. Newton came up with rules and differential equations which produced excellent laws which explained most things. We got to the moon on his equations.
  From a classical point of view everything has equal and opposite reactions as per Newton. So the sun pulls on the earth (actually the earth is pushed toward the sun) and the opposite force is the centrifugal force. Case closed.
GMeMs = Me[V^2]/ R   end of story.
  In a similar light an electric voltage turns a motor on and as the motor speeds up an opposite voltage is produced. So whether electricity or gravity Newton’s laws are true.
  Einstein sought to explain small variations of planetary motion which were not solved by Newtonian physics. So he came up curved space time and his equations proved to be true. The question I ask is whether space curves or the gravitational field curves.
  We also want to know what produces the centrifugal force. From the electrical motor analogy, there is an opposite force built up to the applied force. So the Earth spins around the sun and as it does, an applied force is built up.
  For the electrical motion, the counter force was due to the speed of the motor and the applied magnetic field. So from a classical point of view it can be argued that the centrifugal force is due to the motion of the Earth as it cuts the suns gravitational field. Electrically his would be an eddy current. From a gravitational classical viewpoint, it would be a classical gravitational eddy current. Thus the gravitational field acts like an electric field. That is certainly possible.
  Then we are left with the problem of why from a classical point of view that an object resists a force. As a force is applied gravitational eddy currents are produced which oppose the force. This is caused by the interaction of the object and the gravitational field of the object. After the object reaches a speed V and the force is removed, the object continues to move in a straight line at velocity V. Again no fancy concepts are necessary just classical type theory.
   For this case we get a combination of two forces that makeup the centrifugal force. A reaction of the earth cutting the suns field and a reaction of the Earth with its own field. Pure classical theory. Nothing fancy required. And perhaps the two component answer is better than my original answer.
  The problem with Einstein’s theory is that it is purely mathematical. It does not tell you the details of what is happening. Classical theory does.
Title: Re: What is centrifugal force?
Post by: rmolnav on 29/10/2016 19:25:28
#101 jerrygg38 says:
"From a classical point of view everything has equal and opposite reactions as per Newton. So the sun pulls on the earth (actually the earth is pushed toward the sun) and the opposite force is the centrifugal force. Case closed”.Let me “open” it.
Not being sufficiently careful with our expressions, is a frequent cause of misunderstandings.
“Everything” has NOT equal and opposite reactions … Forces exerted on objects by other objects do.
Is the earth actually “pushed” … ?
“The sun pulls on the earth … and the opposite force is …” Just “the opposite force”? Exerted also on the earth but opposite?
On the other hand, I´m afraid your electricity realm analogy may be useful to some people, but not for the majority. And it is not necessary to understand the subject.   
Title: Re: What is centrifugal force?
Post by: nilak on 29/10/2016 21:24:29
There is something that makes the light go straight. The same thing makes everything travel straight when nothing serious to interact with. To change the course you need to do something. That translates to a force.
Title: Re: What is centrifugal force?
Post by: rmolnav on 30/10/2016 10:58:48
#103 Nilak
Certainly ... Though somebody will tell you light can also be bent by sufficiently massive objects.
But what you say is sufficiently accurate for our "needs"
Newton´s Principles break down that "inertial" fact. But, watch out!, that adjective means just that it is related to "inertia" ... Somebody could relate it to "an inertial system of reference", and try to convince us those reaction forces (f.e.) are only fictitious ...
Title: Re: What is centrifugal force?
Post by: rmolnav on 30/10/2016 11:03:35
#104 (continuation)
Inside the parenthesis I should have added "centrifugal force", the subject of our discussion.
Title: Re: What is centrifugal force?
Post by: jerrygg38 on 30/10/2016 14:21:00
#101 jerrygg38 says:
"From a classical point of view everything has equal and opposite reactions as per Newton. So the sun pulls on the earth (actually the earth is pushed toward the sun) and the opposite force is the centrifugal force. Case closed”.Let me “open” it.
Not being sufficiently careful with our expressions, is a frequent cause of misunderstandings.
“Everything” has NOT equal and opposite reactions … Forces exerted on objects by other objects do.
Is the earth actually “pushed” … ?
“The sun pulls on the earth … and the opposite force is …” Just “the opposite force”? Exerted also on the earth but opposite?

  In newtonian physics the application of a force produces an acceleration where F=MA. The MA is the opposite force. What causes this force? As I see it, the mass has a gravitational field which is moving along with the mass at a velocity V and now the mass has a force applied which increases its velocity and this causes the gravitational field of the mass to resist the motion and thus the opposite force. So you say there are cases where this is not true. However if Newton is right, there are always explanations possible for them to be true for big body motion. Things are different in the world of quantum mechanics where reactions must also include the time dimensions.
   As far as the Earth being pushed toward the sun rather than pulled, this is because the gravitational fields of the Earth and Sun form a center of gravity such that the combined field pushes the sun and earth together.
Title: Re: What is centrifugal force?
Post by: rmolnav on 30/10/2016 18:43:57
#106 jerrygg38
I regret to be rude, but you had better go back to basics. It is not only a question of being more careful with our expressions, as I commented on  #102. There are errors on almost each of your paragraphs.
Only your first paragraph, at least for the moment:
"In newtonian physics the application of a force produces an acceleration where F=MA. The MA is the opposite force"
Utterly misunderstood, and wrong.
The acceleration A is the result of F, what F causes, if and only if the object the force is applied on is free to move.
"A", a vector, has a numeric value (quantity of used units), and a direction and sense (in our three dimension space, in each instant of time).
So, MA is also a vector, logically the "same" of the original force F.
"The opposite force", you can tell thanks to the very adjective, cannot be MA, though its numerical value is the same.
I had previously thought you had basic things not completely clear. That is why I sent #102, and asked:
"“The sun pulls on the earth … and the opposite force is …” Just “the opposite force”? Exerted also on the earth but opposite?"

Title: Re: What is centrifugal force?
Post by: nilak on 30/10/2016 23:04:00
#103 Nilak
Certainly ... Though somebody will tell you light can also be bent by sufficiently massive objects.
But what you say is sufficiently accurate for our "needs"
Newton´s Principles break down that "inertial" fact. But, watch out!, that adjective means just that it is related to "inertia" ... Somebody could relate it to "an inertial system of reference", and try to convince us those reaction forces (f.e.) are only fictitious ...

Obviously what I wanted to point out is, light travels straight when there are no external factors. To bend light you need to do something and that translates to energy.
I've mentioned light, because it is not newtonian principles that makes it go straight. Moment of inertia is not mass preserving its velocity. The motion must have a different explanation. I believe it lies in the way electric and magnetic fields propagate. QM doesn't include these fields which are real, and combines newtonian physics with other properties that can't be expalained claasically resulted from experiments.
I aslo think that all particles in the Standard Model are similar to classical waves and not travelling as separate entities. For example if you make photons go orbiting arround each other you will create the illusion of a particle, but in fact there is an orbital wave that will travel in a spiral and making it slowing down proportionaly to the orbial radius.
If we can't measure to the deepest level what is going on the only option is to create different modes and put them to the test. Until now none has passed  all the tests. This discussion about centrifugal force could, in fact, give us some new clues.
Title: Re: What is centrifugal force?
Post by: rmolnav on 31/10/2016 07:20:42
#107 (continuation)
To put it easier to understand, what you said F=MA="the opposite force" ...
... it´s equivalent to saying: 1=1=-1 !! After that, with all my respects for you, a further discussion about any other of your statements or arguments could be a waste of time. Perhaps that was why Alancalverd and PmbPhy are "missing" ...
But I´ll try and carry on ... It could be useful, if not to you, to somebody else.
Title: Re: What is centrifugal force?
Post by: jerrygg38 on 31/10/2016 12:33:16
There is something that makes the light go straight. The same thing makes everything travel straight when nothing serious to interact with. To change the course you need to do something. That translates to a force.
Light around a star
  The question of what makes light go straight is the geometric nature of dot-waves. The photonic dot-waves consist of positive and negative charges which are separated by half a wavelength. The same is true of the photon which consists of huge numbers of dot-waves. When the negative dot-wave is at a zero point, the positive dot-waves is at maximum radius. The positive dot-wave attracts the negative and flows toward it. As it does it contracts but the negative expands. Thus the photon is a motor mechanism which goes from a point to a spherical surface and back to a point as it travels at the speed of light C.
  For an object moving at velocity V, it contains billions of billions of photonic oscillations which produce a straight line motion.
  When a photon travels close to a star, it encounters dot-waves traveling around the star. It absorbs some of these mini-photons which produce a new vector image and the photon bends around the star. As it leaves the vicinity of the star into lower gravitational fields, it loses some dot-waves and continues on its way.
Title: Re: What is centrifugal force?
Post by: nilak on 31/10/2016 15:51:01
There is something that makes the light go straight. The same thing makes everything travel straight when nothing serious to interact with. To change the course you need to do something. That translates to a force.
Light around a star
  The question of what makes light go straight is the geometric nature of dot-waves. The photonic dot-waves consist of positive and negative charges which are separated by half a wavelength. The same is true of the photon which consists of huge numbers of dot-waves. When the negative dot-wave is at a zero point, the positive dot-waves is at maximum radius. The positive dot-wave attracts the negative and flows toward it. As it does it contracts but the negative expands. Thus the photon is a motor mechanism which goes from a point to a spherical surface and back to a point as it travels at the speed of light C.
  For an object moving at velocity V, it contains billions of billions of photonic oscillations which produce a straight line motion.
  When a photon travels close to a star, it encounters dot-waves traveling around the star. It absorbs some of these mini-photons which produce a new vector image and the photon bends around the star. As it leaves the vicinity of the star into lower gravitational fields, it loses some dot-waves and continues on its way.
This is a resonable explanation, at least for me.

The interaction between dot waves must be extremely low when in the cases when we notice slight deviations from a straight line. This way the photon integrity (like wavelength, particle behavior) is preserved.
Title: Re: What is centrifugal force?
Post by: jerrygg38 on 01/11/2016 12:45:54
#107 (continuation)
To put it easier to understand, what you said F=MA="the opposite force" ...
... it´s equivalent to saying: 1=1=-1 !! After that, with all my respects for you, a further discussion about any other of your statements or arguments could be a waste of time. Perhaps that was why Alancalverd and PmbPhy are "missing" ...
But I´ll try and carry on ... It could be useful, if not to you, to somebody else.
   Perhaps with my simple engineering language I did not make it clear what I meant. I see that you are very precise and legalistic in your language.  Returning to:
  F = MA
  On the left side of the equation is the applied force F.  On the right side of the equation is the equal and opposite force MA. What does this mean? It states that a mass that is accelerating produces a force equal and opposite to the applied force. How is that possible?
  A mass has a gravitational field. When the mass is stationary with respect to a particular frame of reference, the field is also stationary. Now let us apply a force to move the mass. The moving mass accelerates and the mass cuts its own field. This induces gravitational current flows in the mass with the result that an equal and opposite force is generated. As the gravitational field of the mass moves to the same steady state velocity as the mas itself, no more resisting force is generated and the mass continues to move at velocity V until another force is applied. thus the equal and opposite force only occurs when a new force is applied to the mass.
Title: Re: What is centrifugal force?
Post by: rmolnav on 02/11/2016 11:03:33
#112 jerrygg38
I Insist: you had better going back to basic Mechanics. You say absurd things relative to “gravitational fields”, perhaps because you don´t actually grasp its meaning.
You seem to consider that "A mass has a gravitational field”, sort of rucksack carried by the mass. That is utterly erroneous, but even if it were right, you say contradictory things:
"the gravitational field of the mass moves to the same steady state velocity as the mas itself”
 "The moving mass accelerates and the mass cuts its own field"
Why that “rucksack” moves with the mass when constant velocity, but can´t accelerate with the mass, and the field is cut by the mass “carrying" the field?
NONSENSES … By the way, no wonder you say such things, because you also said (#0):
“… In this case the centrifugal force does not have to exist but is merely a vector caused by the momentum of the ball and the length of the string”
MERELY A VECTOR? What do you think is a “mere vector”? Are not all forces represented by vectors?
I can´t really understand why you talk about gravitational fields, apparently so convinced, having such Physics/Maths education gaps.
Title: Re: What is centrifugal force?
Post by: rmolnav on 04/11/2016 19:10:52
I was planning to draft and send a post referring to something I´ve lately begun to think, after discussing so much here:
Perhaps modern physicists who say it would be better not to use the expression “centrifugal force” are right. But not because it is not a real force, but because it is frequently used even by laymen, and its different flavors are really difficult to grasp. And that easily leads to confussion and errors.
“The devil is in the details” … The subject requires not only that we should have very clear basic concepts, but also that we must be very careful with the details.
I already said nature is much more complex than what our mathematical simplifications show …
A typical misleading error is to say that thanks to centrifugal force things can be given an extra speed (sling, hammer throwing, and even what said on #11-PUPPYPOWER: "We use the moons and planets to sling shot satellites to distant planets. We make use of the centrifugal force …”)
I´ve already said, many times, that centrifugal f. does exist, that it is a force quite REAL.
But due to its very nature, it cannot be the “cause” of mentioned effects.
I was planning to analyze several, frequently missing details, starting with the sling, similar to hammer throwing.
Prepairing the work, I´ve seen that JERRYGG38 also said (#0):
"So we get a law of physics such that "A planet moving with velocity V tangent to the radius from a star will generate a centrifugal force that balances the centripetal force and this keeps the planet from falling into the star”.”
That is also UTTERLY ERRONEOUS. I know many people say that (a piece of the big confusion),  but I challenge him, and anybody else, to find that supposed “law of physics” written on a university or high school book on the subject..
I´ll send mentioned analysis tomorrow on another post.




Title: Re: What is centrifugal force?
Post by: jerrygg38 on 05/11/2016 13:43:51
Rmolnav said:I Insist: you had better going back to basic Mechanics. You say absurd things relative to “gravitational fields”, perhaps because you don´t actually grasp its meaning.
You seem to consider that "A mass has a gravitational field”, sort of rucksack carried by the mass. That is utterly erroneous, but even if it were right, you say contradictory things:
"the gravitational field of the mass moves to the same steady state velocity as the mas itself”
 "The moving mass accelerates and the mass cuts its own field"
Why that “rucksack” moves with the mass when constant velocity, but can´t accelerate with the mass, and the field is cut by the mass “carrying" the field?
Jerrygg replied: There is a time delay between the mass and its field. You move the mass and its field exists as part of a huge field which combines with the fields of others. The field of the earth reaches hundreds of millions of miles from the Earth. The earth is the center of its field. As the Earth moves the field will follow but there is a time delay. The net result is that the Earth which is present time interacts with its field which is prior time. The same is true of a rock but the field of the rock becomes indistinguishable from the Earth’s field in a few miles.
Rmolnav said:… By the way, no wonder you say such things, because you also said (#0):
“… In this case the centrifugal force does not have to exist but is merely a vector caused by the momentum of the ball and the length of the string”
MERELY A VECTOR? What do you think is a “mere vector”? Are not all forces represented by vectors?
Jerrygg replid: Others have concluded that centrifugal force does not exist. I just rephrased what they implied. I believe that centrifugal force exists.
Rmolnav said:I can´t really understand why you talk about gravitational fields, apparently so convinced, having such Physics/Maths education gaps.
Jerrygg replied: I graduated BSEE (summa cum laude) from Brooklyn Polytechnic Institute in 1966 which I feel was a pretty good education. I never had a test in science or engineering that I got less than 100%.
Title: Re: What is centrifugal force?
Post by: rmolnav on 05/11/2016 18:51:11
#114 (continuation)
After drafting as "notes" what follows, I´ve seen reply 115. I prefer to send it already, and later or tomorrow I´ll read #115 and reply.
 Differences between the case of two celestial objects rotating around their barycenter, and the case when an object is being rotated by us by means of a cord o similar tool (as e.g. in hammer throwing), go beyond the “physical” difference that nothing connects the celestial objects to each other, apart from the “tele-connection" of gravity …
Somehow the celestial objects were initially given their speeds very long ago, and no energy is transferred now from/to each other.
When an athlete initiates hammer rotation, he has to transfer energy to the hammer, in order to increase its tangential speed the more the better.
For the sake of simplicity, i consider a rotation always around a vertical axis. The “tension” of the wire, I mean the inward force, is not strictly “centripetal”. It has three components:
One vertical, which has to support hammer weight (the wire can´t be completely horizontal).
Another horizontal and centripetal, which produces the centripetal acceleration necessary for the hammer to follow its circular path.
And yet another horizontal but tangential, the usually “forgotten” force. It is due to the fact that athlete hands are also rotating, but the straight line hands-wire-hammer is not a radius of hammer trajectory … The athlete tries and increases the angular speed of his hands, with the purpose of increasing angular and tangential speeds of the hammer, before releasing it. There is a sort of angular “delay” of the hammer relative to the situation of athlete hands. That´s the cause of the tangential component of wire tension.
(I can´t erase this 4 !!) So, the athlete increases more and more wire tension, and both its centripetal and tangential components increases too. Centrifugal force (opposite to centripetal one: the hammer pulling outwards wire end) increases as the centripetal one does… That outward, centrifugal force that increases more and more, could appear to cause the hammer to “fly” when the athlete releases it. But IT IS NOT.  The cause is actually mentioned tangential component of wire tension, that increases velocity revolution after revolution, with continuous transference of energy from the athlete to the hammer … As soon as the wire is released, hammer (+ wire) is “free” and go straight at its acquired tangential velocity (apart from weight and air friction effects).
After all, the centrifugal force was NOT being exerted on the hammer, and even if it had been, it would require time to increase any velocity, but it “dies” at same instant the hammer is released.
So, we can say centrifugal force rol is “important: the wire could not exert any centripetal force on the hammer not being tight, and it could not be tight acting only a force at one of its extremes !!
And don´t forget that, as I´ve been referring to during last weeks, centrifugal forces have other important roles in other cases. I have to decide which case may be worth to insist on.
Title: Re: What is centrifugal force?
Post by: rmolnav on 09/11/2016 12:51:28
#115 jerrygg38
Besides my challenge on #114, if you got your degree where and when you say, I challenge you to find a text book used there with written statements similar to yours. It may not be a problem of Physics/Maths, but of Logics, not always properly kept in mind for so long.
Another key, erroneous idea of you. You said (#0):
"You have a momentum and a gravitational pressure (?) pushing (?) the earth toward the sun. What keeps the earth from falling into the sun?  That is the big problem” Apart from what with my ? within parenthesis, Is that really the big problem? Are you sure that it is not one of YOUR problems, and that earth is not somehow falling at least “toward” the sun? …
It is BASIC Physics. If earth were moving at a higher speed, it could not follow its current orbit, and it would have gone far away from the sun. If at lower speed, sun gravitational PULL would have made earth fall into it.
But earth speed vector is such that, at actual earth distance to sun, the gravitational pull is just what necessary to change earth speed vector direction and make earth follow its orbit.
And that whatever the possible deep nature of gravity: space-time curving originated by the sun, according to Einstein´s theory, or any other …
If you have other (bizarre) ideas, they must be of your own invention, not coming actually from your degree education. You could challenge Newton and Einstein, and apply for a Nobel prize … Be lucky.
By the way, earth/sun case is very, very similar to the center/string/rotating object case wrongly exposed by you at the beginning of #0, as well as to hammer throwing case brought up by me (#116). The unique difference is that sun gravitational pull is exerted independently on every earth molecule, as if there were "infinite” tiny, invisible strings, connecting each molecule to sun (for the sake of simplicity, to its C.G.). And the “tension” of those virtual strings would vary from midday closest areas to antipodes, the closest the higher gravitational pull, and the smaller centripetal force necessary to rotate at 2PI/year angular speed ...
That happens all across the universe, to ANY rotating object. And it is the root cause of ALL tidal effects, because mentioned local imbalances (between gravitational pulls and centripetal forces required for common angular speed of rotation) generate internal stresses/forces, an “infinite” number of action/reaction pairs …
The result of all acting forces is that earth is deformed and tries and get a shape tending, relatively very litle, to a rugby ball. In the closest earth half, centripetal forces dominate over centrifugal ones, and the opposite in furthest half.


Title: Re: What is centrifugal force?
Post by: rmolnav on 14/11/2016 12:24:35
After my last post I´ve been visiting other sites talking about our subject. I couldn´t imagine I was going to find so much confusion.
E.g. many say centrifugal force is only an “apparent” force, because they consider it as if it were exerted on same rotating object as the centripetal, when what actually happens is that it is exerted BY that object on the other (the one exerting  the centripetal).
And some, trying to explain real phenomena where centrifugal f. is root cause, have to build “unbelievable" kind of contraptions.
There are even some well known dictionaries (Collins, Merriam-Webster's Learner's Dictionary, American Heritage Dictionary …). Where possible, I refuted them too. I´ll let you know if any answer.
Fortunately I am not "alone" ... Following link is from an education group, and they say same things I´ve been using to refute others, even with very similar words …
(I´ve also been using the example of hammer throwing with a spring dynamometer between wire extreme and hammer):
http://www.infoplease.com/encyclopedia/science/centripetal-force-centrifugal-force.html
Title: Re: What is centrifugal force?
Post by: nilak on 14/11/2016 12:43:40
After my last post I´ve been visiting other sites talking about our subject. I couldn´t imagine I was going to find so much confusion.
E.g. many say centrifugal force is only an “apparent” force, because they consider it as if it were exerted on same rotating object as the centripetal, when what actually happens is that it is exerted BY that object on the other (the one exerting  the centripetal).
And some, trying to explain real phenomena where centrifugal f. is root cause, have to build “unbelievable" kind of contraptions.
There are even some well known dictionaries (Collins, Merriam-Webster's Learner's Dictionary, American Heritage Dictionary …). Where possible, I refuted them too. I´ll let you know if any answer.
Fortunately I am not "alone" ... Following link is from an education group, and they say same things I´ve been using to refute others, even with very similar words …
(I´ve also been using the example of hammer throwing with a spring dynamometer between wire extreme and hammer):
http://www.infoplease.com/encyclopedia/science/centripetal-force-centrifugal-force.html

It says there that:"The centrifugal force is often mistakenly thought to cause a body to fly out of its circular path when it is released; "
Of course a body is not trying to fly out of its circular path. Instead, the body is trying to keep its straight line trajectory. But being constantly corrected by the force in the string it moves in a circular path and also generates an inertial force, which is the centrifugal force. That is what it says here. If the body is conected by an string which length increases with time, the inertial force will not be the same formula with the centrifugal force. An eleptical orbit will also generate a different formula for the inertial force pulling outeard.
Title: Re: What is centrifugal force?
Post by: nilak on 15/11/2016 00:46:30
The proof centrifugal force is not fundamental.

A satelite orbiting the Earth is always in free fall.
A roket that uses its thrusters to hover at the same hight without orbiting the Earth is not in free fall.
That is the difference.

The rocket requires constant power. The satelite doesn't.
If you go there to feel the effects you will definitely notice the difference.
In the rocket you will feel a little gravity (in fact is the force from the thrusters equal to gravity)
In the satelite you will feel free falling.

That is simple newtonian.

In GR you replace gravity with falling space itself (equivalent to curved spacetime) and its the same thing.
Title: Re: What is centrifugal force?
Post by: jerrygg38 on 15/11/2016 11:25:26
#103 Nilak
Certainly ... Though somebody will tell you light can also be bent by sufficiently massive objects.
But what you say is sufficiently accurate for our "needs"
Newton´s Principles break down that "inertial" fact. But, watch out!, that adjective means just that it is related to "inertia" ... Somebody could relate it to "an inertial system of reference", and try to convince us those reaction forces (f.e.) are only fictitious ...

Obviously what I wanted to point out is, light travels straight when there are no external factors. To bend light you need to do something and that translates to energy.
I've mentioned light, because it is not newtonian principles that makes it go straight. Moment of inertia is not mass preserving its velocity. The motion must have a different explanation. I believe it lies in the way electric and magnetic fields propagate. QM doesn't include these fields which are real, and combines newtonian physics with other properties that can't be expalained claasically resulted from experiments.
I aslo think that all particles in the Standard Model are similar to classical waves and not travelling as separate entities. For example if you make photons go orbiting arround each other you will create the illusion of a particle, but in fact there is an orbital wave that will travel in a spiral and making it slowing down proportionaly to the orbial radius.
If we can't measure to the deepest level what is going on the only option is to create different modes and put them to the test. Until now none has passed  all the tests. This discussion about centrifugal force could, in fact, give us some new clues.

Nilak said: Obviously what I wanted to point out is, light travels straight when there are no external factors. To bend light you need to do something and that translates to energy.
Jerry replied: That is not necessarily true. When light encounters a gravitational field gradient it may gain energy or lose energy. However to bend light no energy is required. You only need a gradient differential in momentum.  The light around the sun will absorb some  sub-photonic particle/waves circling around the sun and some emit straight line sub-photonic particle/waves. Thus there is a transfer of momentum but not energy.
Nilak said: I've mentioned light, because it is not newtonian principles that makes it go straight. Moment of inertia is not mass preserving its velocity. The motion must have a different explanation. I believe it lies in the way electric and magnetic fields propagate. QM doesn't include these fields which are real, and combines newtonian physics with other properties that can't be expalained claasically resulted from experiments.
Jerry replied:Yes, photons travel in a straight line by the geometric structure of the light wave. The photons in my opinion have two parts which attract each other. When on part is enlarging, the other part is shrinking. One reaches maximum radius and the other reaches a point. And the cycle continues. The result is that the pattern always forms a perfect straight line. Pure simple geometry. And because both halves exist in different small time dimensions, they can never destroy each other. But they can turn into mass which involves a spherical energy configuration.
Nilak said:I aslo think that all particles in the Standard Model are similar to classical waves and not travelling as separate entities. For example if you make photons go orbiting arround each other you will create the illusion of a particle, but in fact there is an orbital wave that will travel in a spiral and making it slowing down proportionaly to the orbial radius.
If we can't measure to the deepest level what is going on the only option is to create different modes and put them to the test. Until now none has passed  all the tests. This discussion about centrifugal force could, in fact, give us some new clues.
Jerry replied: I am certainly learning a lot from it. I see certain possibilities but the various answers may only be partial components of the centrifugal force. But to maintain Newton, it must be an equal and opposite force. Yet this force could have several components.  When we swing the rock on a rope, something is pulling against us. And at the moment the best I can think of is the rock is interacting with its own gravitational field. Yet that may only be a partial solution and the rock may be interacting with the gravitational field of the Earth which is a stronger field. What happens aboard a spaceship where the Earth’s field is low?
Title: Re: What is centrifugal force?
Post by: rmolnav on 15/11/2016 19:22:27
#119 Nilak
What you quoted is not what I mainly wanted to show from what  linked, which is just before:
"According to Newton's third law of motion, for every action there is an equal and opposite reaction. The centripetal force, the action, is balanced by a reaction force, the centrifugal ("center-fleeing") force. The two forces are equal in magnitude and opposite in direction. The centrifugal force does not act on the body in motion; the only force acting on the body in motion is the centripetal force. THE CENTRIFUGAL FORCE ACTS ON THE SOURCE OF THE CENTRIPETAL FORCE to displace it radially from the center of the path. Thus, in twirling a mass on a string, the centripetal force transmitted by the string pulls in on the mass to keep it in its circular path, while the centrifugal force transmitted by the string pulls outward on its point of attachment at the center of the path".
But you talk of two forces acting on same unique rotating object: centripetal f., and an inertial f. which you, and many others, consider to be the centrifugal f.
As I have said many times, that is NOT the REAL centrifugal force, which comes from 3rd Newton´s Principle, as a reaction to centripetal f., and should not be considered acting on the very rotating object ...
That´s why many people say centrifugal f. is just apparent, fictitious ... And it originates an unbelievable confusion out there !!
Title: Re: What is centrifugal force?
Post by: nilak on 15/11/2016 21:06:33
Quote
Jerry replied: That is not necessarily true. When light encounters a gravitational field gradient it may gain energy or lose energy. However to bend light no energy is required.
You are right, no energy is required.
When light is curved under a gravitational field, we can still say it travels straight. The space itself is dynamically modifying its geometry.
Since the gravity is not a force, in this context it means the centrifugal force does not exist in planetary system under gravity.

The problem is, we don't have a theory of everything and we keep crossing between newtonian mechanics and GR.
Title: Re: What is centrifugal force?
Post by: jerrygg38 on 16/11/2016 14:04:55
Quote
Jerry replied: That is not necessarily true. When light encounters a gravitational field gradient it may gain energy or lose energy. However to bend light no energy is required.
You are right, no energy is required.
When light is curved under a gravitational field, we can still say it travels straight. The space itself is dynamically modifying its geometry.
Since the gravity is not a force, in this context it means the centrifugal force does not exist in planetary system under gravity.

The problem is, we don't have a theory of everything and we keep crossing between newtonian mechanics and GR.

Nilak said: You are right, no energy is required.
When light is curved under a gravitational field, we can still say it travels straight. The space itself is dynamically modifying its geometry.
Jerry replied: To say that space itself is modifying its geometry  presents something mysterious called space. All we know is that the photon is traveling along a gravitational field that changes the vector angle of the light without changing its energy level. What happened? The intensity of the gravitational field is stronger toward the sun and weaker away from the sun. The stronger side will gain energy and the weaker side will lose energy. The net gain and loss will be zero. This will cause the photon vector to change and the light will bend around the sun. Once you leave the strong gravitational field of the sun, the photonic vector will equalize and the photon will continue on a straight line. No strange space is required, just simple Newtonian type physics.
Nilak said: Since the gravity is not a force, in this context it means the centrifugal force does not exist in planetary system under gravity.
Jerry replied: Just as the photon will bend due to differential gravity, the Earth will  curve around the sun. So the mechanism for planetary orbits is that the momentum of the earth has a twist in it due to the gravitational field differential. It is just a classical physics problem with Einsteinian velocity corrections.
   You may be correct in saying that this is not a regular centrifugal force problem because scientists have not considered the twist of objects moving in a gravitational field. There is no such thing as a object moving in a straight line forever. An object will always curve due to the gravitational field gradient.
Nilak said:The problem is, we don't have a theory of everything and we keep crossing between newtonian mechanics and GR.
Jerry replied: Newtonian mechanics is good engineering analysis. GR is a mathematicians analysis. Both are good but as an Engineer I want to know what is happening and GR does not explain the twist of objects moving in a gravitational field. GR mathematically stays that space is curved but that is false. The gravitational field causes space to appear curved. So Einstein is mathematically correct but from a nuts and bolts engineering understanding Einstein does not explain what is happening.
Title: Re: What is centrifugal force?
Post by: nilak on 16/11/2016 16:30:20

Nilak said: You are right, no energy is required.
When light is curved under a gravitational field, we can still say it travels straight. The space itself is dynamically modifying its geometry.
Jerry replied: To say that space itself is modifying its geometry  presents something mysterious called space. All we know is that the photon is traveling along a gravitational field that changes the vector angle of the light without changing its energy level. What happened? The intensity of the gravitational field is stronger toward the sun and weaker away from the sun. The stronger side will gain energy and the weaker side will lose energy. The net gain and loss will be zero. This will cause the photon vector to change and the light will bend around the sun. Once you leave the strong gravitational field of the sun, the photonic vector will equalize and the photon will continue on a straight line. No strange space is required, just simple Newtonian type physics.
Nilak said: Since the gravity is not a force, in this context it means the centrifugal force does not exist in planetary system under gravity.
Jerry replied: Just as the photon will bend due to differential gravity, the Earth will  curve around the sun. So the mechanism for planetary orbits is that the momentum of the earth has a twist in it due to the gravitational field differential. It is just a classical physics problem with Einsteinian velocity corrections.
   You may be correct in saying that this is not a regular centrifugal force problem because scientists have not considered the twist of objects moving in a gravitational field. There is no such thing as a object moving in a straight line forever. An object will always curve due to the gravitational field gradient.
Nilak said:The problem is, we don't have a theory of everything and we keep crossing between newtonian mechanics and GR.
Jerry replied: Newtonian mechanics is good engineering analysis. GR is a mathematicians analysis. Both are good but as an Engineer I want to know what is happening and GR does not explain the twist of objects moving in a gravitational field. GR mathematically stays that space is curved but that is false. The gravitational field causes space to appear curved. So Einstein is mathematically correct but from a nuts and bolts engineering understanding Einstein does not explain what is happening.

Space is something misterious but GR amost solved the mistery.
Curved spacetime is equivalent to space that is changing geometry in time. I prefer to present it first time like a changing geometry in time rather spacetime block.  After visualizing this space vs. time concept, you can go interpret spacetime concept.
Light can travel in a space that is changing geometry but cannot travel in spacetime. In spacetime light is a static single 4d picture. If you ommit z axis, and use a 2d +1t spacetime you get a block 3d spacetime. Nothing moves there because time is already included.
An object  following a geodesic line is misleading.

In our universe there is nothing moving in a perfect straight line of course. However in a hypothetical scenario a beam o light in a static space will move in a straight line. The static space can have different energy densities, but light will still go straight if the geometry of space is fixed. Notice I used the notion of space not spacetime. If you use spacetime, then you know what happens to the space over time.

Newtonian mechanics cannot be used for explaining reality at a fundamental level. The closest thing to fundamental level is GR and Einstein equations.
To solve fundamental problems we can use GR and perhaps make some speculations. But in my opinion newtonian mechanics is obsolete for solving problems at a fundamental level.
Title: Re: What is centrifugal force?
Post by: jerrygg38 on 16/11/2016 22:56:46
Nilak said: In our universe there is nothing moving in a perfect straight line of course. However in a hypothetical scenario a beam o light in a static space will move in a straight line. The static space can have different energy densities, but light will still go straight if the geometry of space is fixed. Notice I used the notion of space not spacetime. If you use spacetime, then you know what happens to the space over time.
Jerry replied: You have interesting points in your understanding of Einsteinian space time. It makes for a very complex universe that few can understand.  I believe that the universe is a much more simple place that many, many people can readily understand.
   You say that light will go straight in the geometry of space is fixed.  When I look at a photon traveling through a parallel to a fixed gravitational field, if we look inside the photon we will find (in my opinion) that the energy density is higher on the side facing the stronger gravitational field. Thus the photon may maintain the same total energy but it has more energy on the side facing the stronger field. In effect there was an energy shift within the photon itself and the photon will curve.
  For our universe with the center of the gravitational field at the big bang, the light will curve around the universe. Thus fancy space time is not necessary to explain the universe.
  Classical theory with added Einsteinian velocity corrections and elements of string theory small dimensions plus the strange quantum mechanical effects produce a universe from an engineering perspective. Then the question becomes if the universe is an engineering marvel or a mathematical puzzle. Both are possible  but I like the former.
Title: Re: What is centrifugal force?
Post by: nilak on 16/11/2016 23:41:13
Actually light cannot move in a static space beacause it automatically changes the geometry of space as it travels but you can imagine a static homogeneous infinite space before you release a EM wave, which will go straight.
All I want to say is that deviation of light occurs only where and while space changes geometry. Of course if you treat the photon quantum mechanically things get a bit messed up but again the probability to go straight is the highest.
Title: Re: What is centrifugal force?
Post by: nilak on 17/11/2016 10:58:12
By newtonian mechanics, an object that travels in a gravitational filed gains kinetic energy and loses potential energy, hence no energy input. But in there is no gravitational field the object goes straight. If you magically introduce a large object with mass that createa a gravitational filed, the object will deviate from a straight line. The introduction of the massive object means introducing energy into the system. This means the object genuinely travels straight. To deviate it you need energy.
If the massive object was already present the deviation was already in progress hence no energy transfer.
That is the difference.
Title: Re: What is centrifugal force?
Post by: jerrygg38 on 17/11/2016 12:08:51
Nilak said: Actually light cannot move in a static space beacause it automatically changes the geometry of space as it travels but you can imagine a static homogeneous infinite space before you release a EM wave, which will go straight.
All I want to say is that deviation of light occurs only where and while space changes geometry. Of course if you treat the photon quantum mechanically things get a bit messed up but again the probability to go straight is the highest.
Jerry replied: The question is “To be or not to be”. Does space really exist? Is space something? Somehow magical space does something. If space does not exist and only the electromagnetic fields and the gravitational field exists, plus dark matter and low energy  dark energy photons, then we have to define how things operate in terms of these things. That leads us to classical engineering  type problems and solutions.  So we can look at the universe in terms of properties of space and time or in terms of the stuff within space. We then have two choices, a mathematical solution defined by the properties of space and time and an engineering solution where we seek to understand what is happening within the stuff within space.
  So for the mathematical solution you say that light cannot move in static space because it changes the geometry of space as it travels.  At first these words were strange to me but as I dwell on them for the mathematical solution a light wave must react with space in order to survive. Ok that makes sense for the case where space is something.
Nilak says” By newtonian mechanics, an object that travels in a gravitational filed gains kinetic energy and loses potential energy, hence no energy input. But in there is no gravitational field the object goes straight. If you magically introduce a large object with mass that creates  a gravitational filed, the object will deviate from a straight line. The introduction of the massive object means introducing energy into the system. This means the object genuinely travels straight. To deviate it you need energy.
If the massive object was already present the deviation was already in progress hence no energy transfer.
That is the difference.
Jerry says: There are two possibilities. An object can have its own gravitational field that travels with it or space creates the gravitational field. If an object has its own gravitational field then this field is 13.78 billion light years in size.  Thus what we see in a particle is a focal point of what it is. An alternative is that a particle interacts with the dark energy photonic field to create the gravitational field. In either case space has no properties. Other alternatives is that the various fields are physically separated from each other by tiny differences in time. Thus the positive and negative electric fields never coexist.
  We then have many possibilities from space is nothing to space is everything. Photons can interact with space or photons can be independent of space. Another possibility is that space is merely a different state of the gravitational field. We say that the gravitational field has  deviation in intensity and thus a direction. Yet it is possible for the field to be neutral. Thus the gravitational field can be looked upon as clay that can be molded and twisted into interesting shapes. There are many interesting possibilities for sure.
Title: Re: What is centrifugal force?
Post by: nilak on 17/11/2016 18:04:08
Nilak said: Actually light cannot move in a static space beacause it automatically changes the geometry of space as it travels but you can imagine a static homogeneous infinite space before you release a EM wave, which will go straight.
All I want to say is that deviation of light occurs only where and while space changes geometry. Of course if you treat the photon quantum mechanically things get a bit messed up but again the probability to go straight is the highest.
Jerry replied: The question is “To be or not to be”. Does space really exist? Is space something? Somehow magical space does something. If space does not exist and only the electromagnetic fields and the gravitational field exists, plus dark matter and low energy  dark energy photons, then we have to define how things operate in terms of these things. That leads us to classical engineering  type problems and solutions.  So we can look at the universe in terms of properties of space and time or in terms of the stuff within space. We then have two choices, a mathematical solution defined by the properties of space and time and an engineering solution where we seek to understand what is happening within the stuff within space.
  So for the mathematical solution you say that light cannot move in static space because it changes the geometry of space as it travels.  At first these words were strange to me but as I dwell on them for the mathematical solution a light wave must react with space in order to survive. Ok that makes sense for the case where space is something.
Nilak says” By newtonian mechanics, an object that travels in a gravitational filed gains kinetic energy and loses potential energy, hence no energy input. But in there is no gravitational field the object goes straight. If you magically introduce a large object with mass that creates  a gravitational filed, the object will deviate from a straight line. The introduction of the massive object means introducing energy into the system. This means the object genuinely travels straight. To deviate it you need energy.
If the massive object was already present the deviation was already in progress hence no energy transfer.
That is the difference.
Jerry says: There are two possibilities. An object can have its own gravitational field that travels with it or space creates the gravitational field. If an object has its own gravitational field then this field is 13.78 billion light years in size.  Thus what we see in a particle is a focal point of what it is. An alternative is that a particle interacts with the dark energy photonic field to create the gravitational field. In either case space has no properties. Other alternatives is that the various fields are physically separated from each other by tiny differences in time. Thus the positive and negative electric fields never coexist.
  We then have many possibilities from space is nothing to space is everything. Photons can interact with space or photons can be independent of space. Another possibility is that space is merely a different state of the gravitational field. We say that the gravitational field has  deviation in intensity and thus a direction. Yet it is possible for the field to be neutral. Thus the gravitational field can be looked upon as clay that can be molded and twisted into interesting shapes. There are many interesting possibilities for sure.

Yes, I agree. Space as everything is an alternative but not necessarily the best one, it just, for me makes more sense.
Title: Re: What is centrifugal force?
Post by: rmolnav on 18/11/2016 12:14:00
Let us go BACK TO BASICS.
We don´t know what the root essence of gravity, and space, actually is.
But for most of our practical applications Newton´s theories are sufficient.
Following them, and as far as I can understand, if an object with a mass A is in a certain point of space (in an instant of time), it WOULD exert a gravitational pull on another object with mass B IF the second WERE placed in another point, directly proportional to both masses A and B, and inversely to the square of their separation.
Then somebody thought it could be mathematically useful a tool such as vector field, now gravitational field of A, formed by all vectors representing the pulls that A WOULD exert on objects of a unit of mass, IF they WERE situated in every point around A.
Those capital letters are there to put emphasis on the fact that gravitational field is actually an abstraction, not a physical reality. In the infinite number of points around A where no massive object in considered instant, the field has only a “potential” reality.
If A changed position, ALL pull vectors would change accordingly, in value and direction (only in value where in line with both positions of A). Initial gravitational field of A, not being something real but just an abstraction, “dies” same moment when mass A changes position.
To consider a gravitational field is something real, can drive people to say nonsenses, such what has often been said here.
E.g. "Another possibility is that space is merely a different state of the gravitational field ..."
That is similar to saying that my face could be a different state of the image I see when looking at a mirror ...
Title: Re: What is centrifugal force?
Post by: jerrygg38 on 18/11/2016 13:52:22
Nilak said: Yes, I agree. Space as everything is an alternative but not necessarily the best one, it just, for me makes more sense.
Jerry replied: The only thing that appears correct to me is that space is not a checkerboard upon which the universe exists. That is only a measurement. This means that at big bang or maximum compression, the universe existed within a much smaller volume. Outside that volume was nothing at all. Thus space itself has no properties but only possibilities.
  Now we compress what you call space. Okay that is good. But what did we really compress? I believe it is the gravitational field that we compressed. At that time this field is the substance of everything. It is amorphous. It can produce mass. It can produce the gravitational field that we measure. It can produce the two electric fields of positive and negative. It can produce the tiny time dimensions (alternatively the positive dimension and the negative dimension.
  Thus the electric fields and the associated magnetic fields are derived from the amorphous gravitational fields. Mass is merely the compressed amorphous gravitational field.
  To make sense of things I need a positive dimension and a negative dimension. Alternately these could be considered tiny time dimensions. So the string theory scientists have conceived of many tiny dimensions. The amorphous gravitational field when compressed can produce many of these dimensions.
  The only thing that bothers me about Einstein’s work is the lack of a differential mass in the forward and rearward directions. And we always have the possibility that mass/energy is slowly radiating into the world of dark energy. This would cause the universe to expand and the back pressure would be gravity.
  Thus many possibilities exist. Einstein’s work provide us with the binding energy of the hydrogen atom as the differential energy of the electron in the first Bohr orbit. His equations provide us with the energy level or the neutrino as the electron is crushed toward the proton. Thus his mathematics is the basis of the big world of the universe and the tiny world of the atom.
   I have been studying this since 1981 as a hobby and I see many possibilities. It is an interesting puzzle.
Title: Re: What is centrifugal force?
Post by: jerrygg38 on 18/11/2016 14:09:19
Rmolnav said: Let us go BACK TO BASICS.
Those capital letters are there to put emphasis on the fact that gravitational field is actually an abstraction, not a physical reality. In the infinite number of points around A where no massive object in considered instant, the field has only a “potential” reality.
If A changed position, ALL pull vectors would change accordingly, in value and direction (only in value where in line with both positions of A). Initial gravitational field of A, not being something real but just an abstraction, “dies” same moment when mass A changes position.
Jerry replied: For any electrical type phenomenon there is a transient solution. The movement of a stationary mass at point A to point B causes the gravitational field to shift. In general there will be a time delay while the shift is taken place. Since the field reaches quite far out, the transient will take quite a long time to settle. In general the field from the mass around point A combines with other fields from nearby masses so it is difficult to find the individual field. However as we see from the gravitational field sensors, we can pick up the field of rotating black holes very far away. Since we can measure such things, the gravitational field is a reality and not an abstraction.
Rmolnav said: E.g. "Another possibility is that space is merely a different state of the gravitational field ..."That is similar to saying that my face could be a different state of the image I see when looking at a mirror ...
Jerry replied: In my prior write up I used the term amorphous gravitational field. So I believe that you are correct. If we compress this field, we get mass and the ordinary gravitational field which I call a bipolar field and the positive and negative electric fields.
Title: Re: What is centrifugal force?
Post by: rmolnav on 21/11/2016 12:15:59
#133 jerrygg38
Firstly, I was referring to gravitational fields, not electrical type phenomena. And within Newton´s Mechanics, which, according to all I´ve read so far, is sufficiently accurate for most of let us say "normal" cases ...
And I find very surprising that somebody who said here (#12):
"... you say General Relativity causes space time to curve. How can general relativity cause space time to curve? Why? This makes no sense. Somehow there is a Sky God called "general relativity" that causes planets and photons, etc. to move in curved paths. This is pure magic and very unscientific for sure. The mathematicians may be happy so say such things but as an Engineer I do not believe it"
NOW finds that:
"...we can pick up the field of rotating black holes very far away. Since we can measure such things, the gravitational field is a reality and not an abstraction".
What detected by LIGO were the so called gravitational waves, considered to be fluctuations in the curvature of spacetime which propagates as waves, traveling outward from the source. Predicted by Einstein's theory of general relativity, the waves transport energy known as gravitational radiation. Sources of gravitational waves include binary star systems composed of white dwarfs, neutron stars, or black holes. Other much less massive objects, as our sun, could also be a source, but they would be too tiny to be detected.
Do you choose from relativity theory only what seems to match your bizarre ideas?
Do you really think that even a toddler, when he finds difficult to accelerate a little bit, it is because when he reaches another position he continues being gravitationally attracted by “himself" situated at his initial position ??… That would mean that gravitons, or whatever actually “transmitting" gravity, are slower than the toddler !!!
You know, somewhere I read the transmission of gravity has same velocity as light. They had found that measuring delays of sun and moon related earth tides … It could not be not so much, but slower than a toddler ???

Title: Re: What is centrifugal force?
Post by: jerrygg38 on 24/11/2016 12:09:30

Rmolnav said: What detected by LIGO were the so called gravitational waves, considered to be fluctuations in the curvature of spacetime which propagates as waves, traveling outward from the source. Predicted by Einstein's theory of general relativity, the waves transport energy known as gravitational radiation. Sources of gravitational waves include binary star systems composed of white dwarfs, neutron stars, or black holes. Other much less massive objects, as our sun, could also be a source, but they would be too tiny to be detected.
Jerrygg38 replied: The question is what is the curvature of space time? To me it is the concentration of the gravitational field. Thus the intensity of the field is greater at the point of curvature. So it is the field that is curved. Another possibility is that the curvature of Einsteinian space time means that the gravitational constant G is a variable. Of course over time a variable G will help the universe to oscillate from min to max to min again.
Rmolnav said: Do you choose from relativity theory only what seems to match your bizarre ideas?
Jerrygg replied: I seek to understand the physical meaning of what the theory predicts.  To use the term space time does not tell us what is happening from a physical viewpoint.
Rmolnav said: Do you really think that even a toddler, when he finds difficult to accelerate a little bit, it is because when he reaches another position he continues being gravitationally attracted by “himself" situated at his initial position ??… That would mean that gravitons, or whatever actually “transmitting" gravity, are slower than the toddler !!!
Jerry replied: It is all happening at the speed of light so the initial position fades away quite rapidly and we get an interaction between the present position and the prior position of a split second ago.
Title: Re: What is centrifugal force?
Post by: rmolnav on 26/11/2016 11:17:17
#135 jerrygg38
I must say I find your last post more let us say reasonable than others. Perhaps the problem is that you are trying something kind of impossible.
You say:
"To use the term space time does not tell us what is happening from a physical viewpoint"
I fully agree with you. But you know,  I´ll never forget (long ago) my best teacher of Maths at the University, late Julio Fernández Biarge (google it and you´ll see ...), telling us something like:
In a plane, a two dimension space, if the addition of the squares of two variables has to keep constant, all we know all points satisfying that condition make a circumference ...
If in our three dimension space, the same has to happen with three variables ... a sphere (very "similar" to a circumference)
We can extrapolate that to a four dimension "imaginary" (not sure whether he used that word), with the addition of the squares of four variables having to keep constant. We could call that "abstract" object a four dimension sphere (a hypersphere in a four dimension space? ) ...
But please, DON´T TRY TO IMAGING AND "SEE" IT IN YOUR MINDS, EVEN AS SOMETHING SOMEHOW SIMILAR TO THE "NORMAL" THREE DIMENSION SPHERE. IT WOULD BE REALLY FRUSTRATING ... 
Title: Re: What is centrifugal force?
Post by: puppypower on 26/11/2016 11:53:35
Centrifugal force appears anytime something rotates or revolves around an axis. Therefore, centrifugal force has a connection to angular momentum. Since centrifugal force does not appear during linear motion, but only starts to appear if the path shows the slightest curvature, suggests that linear momentum is a ground state that gains potential when centrifugal force appears.

If we look at GR and the curving of space-time, since paths in space-time are no longer linear, GR adds centrifugal force because space-time deviates from the ground state of linear motion, where there is no curvature; of space-time. The expansion of the universe is causing universal gravity to curve space-time less and less; space-time expands while mass remains constant. This action is removing centrifugal force potential, back toward the linear momentum ground state. The loss of centrifugal force, with energy conserved, equals an accelerated expansion.
Title: Re: What is centrifugal force?
Post by: rmolnav on 28/11/2016 12:44:29
#136 (Continuation)

I consider that the problem is not in the "use of the term space-time" but in how they try to explain us its curvature and its relation to gravitational atraction.

E.g. there are typical analogies such as:

"main-qimg-65276e2942c653d621e0bd0ac1d665ef

… the presence of body/mass bends the space around it forming a curvature, formation of gravitational well … space time gets bent around Earth and moon revolving around it.

...a free body falls in this gravitational well ... for a body in order to save itself from falling into this well , the body should revolve around planet into circular path. Certain tangential velocity v should be maintained by the body and a is the gravitational acceleration with which it is falling (?) into the well".

They show the bending of a two dimension "space" by our Earth, considering it similar to what theoretically happens to the four dimension space-time.

So far so good. But they introduce our Moon, and, as "a free falling body falls in this gravitational well" ... they say that is the gravitational attraction from Earth …

I must say that is just for naive people. To explain Earth gravity (by an analogy) they consider the Moon, if not rotating, would fall into the well, thanks to what we could call “radial inclination” of the bent surface … But that slope drives things “downward” ONLY if there is some other massive object below, another Earth or similar massive object !!!



Title: Re: What is centrifugal force?
Post by: nilak on 28/11/2016 16:04:41
If we look at atoms inside a rotating object, the sum of these atoms orbital momentum gives the total orbital momentum of the object. If the atoms have their own angular momentum(from rotating around their own axis) it doesn't influence the orbital momentum of the object. So it is clear that centrifugal force appears  when you try to change direction of motion and the same kind of force oposes acceleration.
The atom  or any mass particle angular momentum must work the same way, as summation of orbital momentum of the internal  components.
Bosons shouldn't have angular momentum, only spin.
Title: Re: What is centrifugal force?
Post by: syhprum on 28/11/2016 21:18:52
I think it wrong to say that the gravitational waves emitted by a large planet such as Jupiter orbiting the Sun are to weak to be detected not by LIGO like devices of course but they certainly influence other planets and pull them into resonance.
Title: Re: What is centrifugal force?
Post by: rmolnav on 04/12/2016 12:36:22
#21 hamdani yusuf
I´m referring to something rather old, but I remembered that somebody had mentioned the case of passengers in a car, and recently I saw a good physical description of it, which certainly matches with what I´ve said many times ...
You mentioned there:
"In a turning moving car, the road forces the wheels sideway which in turn forces other parts of the car which is then felt by the passengers. The passengers don't receive any force directly from the road".
And I recently saw:
"When the car travels through the curve the passenger's inertia resists acceleration, keeping the passenger moving with constant speed and direction as the car begins to turn. From this point of view, the passenger does not gravitate toward the outside of the car but the car curves to meet the passenger. Once the car contacts the passenger, it then applies a sidewise force to accelerate him or her around the turn with the car. This force is called a centripetal force because its vector changes direction to continue to point toward the center of the car's arc as the car traverses it. Now we know that the car is acting upon the passenger and therefore the passenger must be acting upon the car with an equal and opposite force. We know that this reaction force have to be opposite to the centripetal force, which is directed to the center of the circular motion. Therefore this reaction force is directed away from the center and we call it centrifugal force. It is important to realize that this centrifugal force acts upon the car, not the passenger".
http://schools.wikia.com/wiki/Centrifugal_force
I would add that "Once the car contacts the passenger .." can be applied to the permanent contact between e.g. modern seats adapted to the body and the passenger.
So, it is not only a passenger´s "sensation", as some people say just caused by his tendency to continue on the straight line of his velocity. They are REAL forces which occur as reactions to whatever is forcing them to turn.
The error would be to consider that those forces act on the passenger, as referred to on last quoted phrase.
Anyhow, as i´ve also said several times, reality is more complex: internal centrifugal (and centripetal, of course) forces also act within passenger body, between his different parts ...
But considering the passenger as a single "object", I find the description very good.
Title: Re: What is centrifugal force?
Post by: rmolnav on 11/12/2016 11:12:25
Yesterday I sent another post (#73) to "Why Do We Have Two High Tides A Day?":
http://www.thenakedscientists.com/forum/index.php?topic=49715.msg504169#lastPostAs
As it is directly related to centrifugal forces, I´ll repeat it here:

Last couple of months I´ve been discussing our "issue", and also the sheer concept of centrifugal force, on "livescience". On some of their last web pages they had shown the idea I´m refuting that centrifugal f. is a kind of taboo, something not real …
Some minutes ago I sent them:
"It´s funny. Just a few minutes ago I saw that Lauren Cox, more than six years ago, on a page ALSO FROM LIVESCIENCE,
http://www.livescience.com/29621-what-causes-the-tides.html
showed a stand very, very similar to mine (linking cause of tides to REAL centrifugal forces):
"The moon's gravitational pull on the earth is strong enough to tug the oceans into bulge. If no other forces were at play, shores would experience one high tide a day as the earth rotated on its axis and coasts ran into the oceans' bulge facing the moon.
… As the moon circles the earth, the earth moves in a very slight circle too, and this movement is enough to cause a centrifugal force on the oceans.
… This inertia, or centrifugal force, causes the oceans to bulge on the opposite side facing the moon ..."
I just wouldn´t say "This inertia, or centrifugal force ...". It is a real, "inertial" force, in the sense that it is due to 3rd Newton´s Principle, based (as the other two) on inertia physical REALITY.
http://www.livescience.com/52488-centrifugal-centripetal-forces.html "
Title: Re: What is centrifugal force?
Post by: rmolnav on 14/10/2017 11:41:29
I do hope the lack of comments/replies in last ten months is due to most of you agree with what exposed by me ... Something similar used to happen relative to the sites of LiveScience I linked. But, to my surprise, some day this recent summer (or spring?), they changed to show main article, but saing "Nş of comments: 0", and certainly all comments were gone !! I have to say those sites are headed by articles by some science contributor, but afterwards they don´t usually send any further comment ... As far as I can remember, they were at least three directly related cases, relative to Newton´s 3rd Motion Law, Centripetal and Centrifugal forces, and the reason why we weigh less at the Equator. I´ve recently been sending new comments refuting their errors in several ways, similarly to what I did here last year. Anybody interested, please kindly have a look at them:
https://www.livescience.com/46561-newton-third-law.html
https://www.livescience.com/52488-centrifugal-centripetal-forces.html
https://www.livescience.com/32504-would-i-weigh-less-at-the-equator.html

And please reply if any doubt and/or opposite idea. With further, detailed discussion, I am almost 100% sure I would be able to convince you.


Title: Re: What is centrifugal force?
Post by: Colin2B on 14/10/2017 22:35:41
I do hope the lack of comments/replies in last ten months is due to most of you agree with what exposed by me ...
Vain hope.
There are many reasons why people stop responding to a thread, but unless you get a positive “yes you are right” don’t assume anything. Most likely is that they still disagree.

Haven’t been following this one, might take a look. Can you summarise the main ‘exposure’?
Title: Re: What is centrifugal force?
Post by: rmolnav on 15/10/2017 11:38:08
Thank you. You are right, I can´t assume anything, I just "hope" ...
Im sure you know there is a lot of confusion regarding centrifugal force out there. Last year I refuted erroneous ideas (not only here), I should say "as far as I can understand". But I must also say I feel pretty sure about my stand.
You can tell English is not my mother tongue. And I type with only a finger of each hand ... Before summarizing the main exposure of this thread, in order to save time, I have been looking at your posts of last year last months, to see if you, perhaps in another thread, could have posted something touching the issue. Just to see if you could also be in the for me "erroneous side" (to my surprise, I have found many, many people "there" ...)
Fortunately I´ve found something which shows perhaps you agree with me, al least that you don´t consider centrifugal force as something NOT existing as a real force, just something "apparent", or "ficticious". I´ve only read your nş 1 reply so far:
https://www.thenakedscientists.com/forum/index.php?topic=68827.msg501090#msg501090
I know a ficticious centrifugal f. is frequently used when in a non inertial frame of reference, just supposing it applied to same considered rotating object, the one actually affected only by the centripetal force ... But that DOES NOT mean real centrifugal forces don´t exist !!
Newton´s 3rd law refers to TWO objects (they also could be two parts of an object ...) ... If object A exerts a centripetal force on B (to make it rotate), B exerts on A an equal but opposite force, quite REAL, which has to be called centrifugal ...
That simple! And one can analyze many, many cases, and find clear explanations for them thanks to real centrifugal forces. But without their existence, many errors turn up ! 
Title: Re: What is centrifugal force?
Post by: rmolnav on 15/10/2017 12:45:46
I´ve found another comment of yours:
"… perhaps it helps to consider the force you and your passengers feel as your car goes around a bend.
You all agree you feel what you would describe as a force, it feels real and has a genuine effect of pushing you to one side, however, another part of you knows it is only because you are following a curved path"
https://www.thenakedscientists.com/forum/index.php?action=profile;u=39298;area=showposts;start=450
I would change your last phrase ... That force is due to the fact that you are following a curved path, but to say "only" is misleading ...
Imagine three of you, transversely situated in the car, shoulder to shoulder, and outer shoulders pressing car windows. Just to allow to follow only their curved paths.
Outer window exerts a centripetal force on outer passenger, and, due to that, according to Newton´s 3rd law that passenger exerts a real outward force on the window: centrifugal force ...
And that passenger has to exert also a centripetal force on central passenger, to oblige him to follow a curved path ... Again according to Newton, central passenger exerts an outward force on outer passenger ... Real, centrifugal force. And so on ...
Both mentioned passengers not only feel a "sensation" of being pushed outward ... They are ACTUALLY being pushed outward, by quite REAL forces, exerted by their inner contiguous passengers ...
Especially outer one "suffers" those outward pushes, centrifugal forces, as long as they add up ... He could even get his chest broken, if sufficient speed (not easy in a car!), because his outer shoulder is also being pushed inward.
Also outer window could break. Neither people, nor windows break due to only "apparent" forces !!!
Title: Re: What is centrifugal force?
Post by: puppypower on 15/10/2017 13:09:28
If you look a centrifugal force, this is motion connected to a curved path. What this brings to my mind is a connection to the curvature of space-time.

If we had a large cloud of low mass density, collapsing into a star, a rotation will appear in the cloud, that generates centrifugal force. Gravity causes the mass density to increase, which causes spacetime to contract and increases the  curvature of space-time.  In this case, centrifugal force is a reaction to the action of gravity that also parallels the increasing curvature of spacetime. The centrifugal force vector acts in the same direction one would expect of antigravity. gravity-antigravity action and reaction.

If you look at this closer, centrifugal force, in general and beyond this targeted example, is more connected to a curved path in space, but not in time. It is not exactly moving in terms of the curvature of spacetime but only with respect to space.

If you look at force, which is mass times acceleration, and acceleration is d/t/t, acceleration or d/t/t contains an extra dimension of time, compared to space-time or d-t. 

As such, the centrifugal force follows curvature in space, while generating a force, which has the extra time dimension of acceleration, compared to space-time. Centrifugal force parallels space-time, but it is expressed in a disjointed way as a separated curved path in space, and a separated aspect of time (potential); acceleration.

Say I take a ball in a string and make it move in a curve path. I use force the make the ball move in a curved path in space. I am also generating time potential via the active force. One may then ask does this action cause a reaction in spacetime? The answer may be yes, since the ball has mass and I am generating an antigravity vector wth respect to me. There should be a slight tweak.
Title: Re: What is centrifugal force?
Post by: Colin2B on 15/10/2017 14:47:09
Fortunately I´ve found something which shows perhaps you agree with me, al least that you don´t consider centrifugal force as something NOT existing as a real force, just something "apparent", or "ficticious".
Yes, I think that the fictitious forces, including Coriolis, are poorly named. I tend to think of them as frame dependent forces, so you view their cause or effect differently depending on which frame you are observing from.
Having skimmed over a few posts in this thread I see part of it is about tides. I agree, there is a frame where earth & moon rotate around a common point resulting in centrifugal force pushing tide bulge on opposite side to moon, this is one of the standard ways of analysing tidal effects.
I know some people get het up about centrifugal force because they have read that it is fictitious, or because of the motivating force coming from centripetal acceleration. Problem is that they happily talk about the force pushing them back into a car seat as it accelerates, but that force is no less fictitious because the body is trying to stay still while it is the car seat supplying the force.
Title: Re: What is centrifugal force?
Post by: rmolnav on 16/10/2017 11:49:28
Problem is that they happily talk about the force pushing them back into a car seat as it accelerates, but that force is no less fictitious because the body is trying to stay still while it is the car seat supplying the force.
Thank you, but I´m not quite sure whether you completely agree with me ...
Unless we all keep in mind  that "Newton" reaction forces are as REAL as "primary" action forces, confusion will persist !
Inertia concept is something kind of vague, just a "tendency" (?) of objects NOT to accelerate, keeping constant their speed (or stillness). But Newton laws put it into clear and REAL math-physical stuff, relations between two interacting objects, REAL forces, masses and accelerations ...
In your example, the car seat is certainly supplying the "primary" force. Otherwise the passengers could not accelerate (1st and 2nd laws). But it is equally certain that, as a reaction (3rd law), each passenger supplies a REAL force too, exerted backwards on their respective seat back.
If somehow all passengers but the driver suddenly disappeared, without changing manual gas setting, the car acceleration would increase, because before REAL backward forces were being exerted on their seat backs, which were acting as if in the second scenario a parachute fixed at the car back structure had suddenly opened, exerting a fully "external" force.
Perhaps the problem is also in that adjective. If we consider the hole car as an object, those action and reaction forces are internal, not affecting 2nd law ... But if we are considering separately the car and the passengers, forces exerted by the car on the passengers are external to them, as well as forces exerted by passengers on the car are external to the car. But all of them are equally REAL!
 
Title: Re: What is centrifugal force?
Post by: rmolnav on 17/10/2017 12:09:59
(Continuation of #149)
Sometimes I say "primary force", in the sense of kind of previous, but action and reaction forces actually begin (and finish) acting simultaneously.
In some cases to decide which one should be called "action" is rather tricky ...
In one of previously linked LiveScience sites, the one about centrifugal force, it is said:
" ... This brings us to Newton’s Third Law, which states, “For every action, there is an equal and opposite reaction.” Just as gravity causes you to exert a force on the ground, the ground appears to exert an equal and opposite force on your feet ... ( + something else about centrifugal force). In each of these cases, though, there is only one real force being applied, while the other is only an apparent force".
For me there are more than one error in what quoted. Do you agree?
Title: Re: What is centrifugal force?
Post by: rmolnav on 19/10/2017 19:09:50
Insisting in the idea that the precise use of Newton´s 3rd Motion Law is key to avoid most of the existing confusion, especially about our topic (centrifugal force), I´m going to repeat here last comment I´ve sent to one of previously mentioned sites of LiveScience. It touches what mentioned by me on #150, where I finished "Do you agree?" ...
Also the importance of precision in the use of terms such as our "weight" is shown. Apparently it is something quite clear, but, e.g., if in Physics it is the gravity pull exerted by our planet on an our body, its Newton´s 3rd Law "couple" should be the equal but opposite pull exerted by our body on our planet, NOT the push exerted on us by what below our feet !!
"Perhaps I should firstly have said that I find our question:
"Would I Weigh Less at the Equator?"
not sufficiently precise, and possibly the origin of the confussion.
On the one hand, we commonly consider our weight what gauged in a spring scale, vertically compressed by underneath floor upward push, and our feet downward push (transmited by the rest of our body).
As I previously said, even if our planet were a perfect sphere, the scale at the equator would show a smaller figure than at higher latitudes, let alone at poles ...
On the other hand, we could also define "weight" differently: the sum of gravity atraction exerted by our planet on all parts of our body ...
In that last sense, it certainly depends only on the distance between centers of gravity.
What actually happens is that part of that atraction is not felt by the scale (neither by our feet and legs), because it is causing the centripetal acceleration vector (perpendicular to axis of rotation) required for our rotation at an angular speed of 2PI radians a day. And that acceleration is proportional to the radius, much bigger at the equator (apart from changes in vectors´relative direction).
So, what we commonly call our "weight", for that second definition would be a kind of "apparent" weight !!
By the way, NOAA not only says "Gravity has less pull at the equator", as quoted at heading picture ... They also say:
"Our planet is pudgier at the equator than at the poles by about 70,000 feet. This is due to the centrifugal force created by the earth’s constant rotation".
https://oceanservice.noaa.gov/facts/earth-round.html
We couldn´t even say that centrifugal force is "kind of apparent" ... Such force wouldn´t be able to cause that "massive" deformation !!
Title: Re: What is centrifugal force?
Post by: hamdani yusuf on 20/10/2017 10:51:11
(Continuation of #149)
Sometimes I say "primary force", in the sense of kind of previous, but action and reaction forces actually begin (and finish) acting simultaneously.
In some cases to decide which one should be called "action" is rather tricky ...
In one of previously linked LiveScience sites, the one about centrifugal force, it is said:
" ... This brings us to Newton’s Third Law, which states, “For every action, there is an equal and opposite reaction.” Just as gravity causes you to exert a force on the ground, the ground appears to exert an equal and opposite force on your feet ... ( + something else about centrifugal force). In each of these cases, though, there is only one real force being applied, while the other is only an apparent force".
For me there are more than one error in what quoted. Do you agree?

I'd like to know how you interpret Newton's third law. Does it mean that total force of any system is always zero?
Title: Re: What is centrifugal force?
Post by: puppypower on 20/10/2017 12:48:19
When I look at centrifugal force, the curved path reminds me of the curvature of space-time that is induced by Relativity. For example, in the case of the moon going around the earth, gravity is causing a contraction and curvature of space-time, with the moon following a curve path. The centrifugal force vector is opposite to that of gravity and therefore would have the opposite affect on space-time. 

If you look the hydrogen atom, to make it simple, its election moves at about 1/137, the speed of light. That means there is some electron based Special Relativity affect, due to this significant velocity of the election.  At this velocity the electron is in a slightly different space-time reference than the proton. The electron's clock runs slower.

However, since the election is using a curve orbit in the 1S orbital, there is a centrifugal force, whose force vector is in the opposite direction of the EM force vector, that binds the electron and proton. If the centrifugal force was connected to space-time, the centrifugal force vector is implicit of expanded space-time. Theoretically this would speed up the election clock and move the election closer to the same reference as the proton; less uncertainty due to relative references closer to the same reference.

The centrifugal force in atoms is not always a space-time wash. In the case of the metal, gold, its outer election velocity is high enough, and the centrifugal force low enough, to remain relativistic differences between the nucleus and the election cloud. The yellow color of gold is due to a relativistic time or frequency shift in reflected energy see relativistic quantum chemistry.
Title: Re: What is centrifugal force?
Post by: rmolnav on 21/10/2017 11:47:38
I'd like to know how you interpret Newton's third law. Does it mean that total force of any system is always zero?
Thank you.
Being very careful as I insist we have to be, I answer that it depends on what you mean with "total force of any system" ...
Newton´s third law is about two interacting objects (let us call them A and B). They exert on each other opposite equal forces. In the first place, adding up those two vectors (certainly resulting zero) has no sense, because they affect two different objects ... And I´m afraid that is the main reason of the existing confusion, especially about centrifugal f.
Other forces could be being exerted on A and/or B by other objects, and A, B, or both could be moving at any pace (with or without acceleration). Whatever their movement, if A exerts a force on B, B will be exerting an equal but opposite force on A.
And that also can be applied to two parts of a single object. I remember I talked about that time ago, more than once ... Please kindly have a look at #37 of this very thread, where I said:
"Imaging just a steel cylindrical bar hanging from one of its ends. If we made a horizontal cut, the lower part would fall down. Why it didn´t fall before? Because of internal tensile stresses: the upper side of the section was pulling the lower one, exactly with a force equal to the weight of lower part of the bar.
If we had made the cut a little lower, we could say the same. In this case the weight of lower part would be a little less: just the weight of the slice between the two cuts.
As the slice is not experiencing any acceleration, the sum of all forces applied to is null. The sum of internal stresses it suffers from contiguous material, plus its own weight, has to be null.
If we produced any upward acceleration to the hanging point, internal stresses would increase in such a way that the sum of weight of the slice plus stresses from contiguous material would give a net force that divided by slice mass would be equal to the acceleration”
You can see how careful one has to be when using 3rd and 2nd Newton´s law. 3rd law is applied here to two different interacting parts of an object (they exert equal but opposite forces on each other), but 2nd to a single slice of the bar (all forces external to the slice will make it move with an acceleration equal to total external forces divided by the slice mass).

 



Title: Re: What is centrifugal force?
Post by: rmolnav on 21/10/2017 12:39:24
For example, in the case of the moon going around the earth, gravity is causing a contraction and curvature of space-time, with the moon following a curve path. The centrifugal force vector is opposite to that of gravity and therefore would have the opposite affect on space-time. 
I must say I haven´t previously commented on your posts because I do not feel sure enough beyond Newton´s Mechanics ...
Perhaps you are right, but watch out ! The essence of centrifugal force in cases such us moon/earth movement is even more "dangerous", prone to confusion, than when not "teleforces" ...
Starting with Newton´s 3rd Law (reason of centrifugal f. reality), the two opposite forces we have are NOT gravity and a centrifugal vector ... They actually are gravity force exerted by earth on moon, and also gravity force but exerted by moon on earth ...
Nevertheless, I´ve several times shown my ideas about centrifugal forces present inside both earth and moon, as internal stresses ... And their condition of partial cause of tidal effects. But I wouldn´t dare connect that to space-time curvature and/or contraction !
 
Title: Re: What is centrifugal force?
Post by: puppypower on 22/10/2017 13:00:21
Let me expand upon my hydrogen atom example and the centrifugal force associated with the electrons of atoms. In hydrogen, the fast moving electron, is in a different space-time reference, compared to the proton, which is not moving as fast; based on Special Relativity. The hydrogen atom has two references in space-time within itself, although we tend to model based on the massive proton.

The countering centrifugal force; opposite the EM force, and its impact on space-time, can explain the quantum nature of atomic emissions.

If we assume the electron and proton are in two space-time references, and the centrifugal force has a vector opposite to the EM force,  it is possible the centrifugal force and its connection to space-time allows situations where the references of the electron and proton merge. These are the quantum sweet spots. The rest of the positions in space and time; orbital, retain two references and will create uncertainty and randomness; probability function.
Title: Re: What is centrifugal force?
Post by: rmolnav on 23/10/2017 12:52:06
Many people consider real centrifugal force doesn´t actually exist, that it is something only apparent or fictitious. This very thread started with a question with that idea.
During last couple of years I´ve been refuting that, theoretically and with many practical examples.
In all cases I´ve seen that real force is associated with either two objects in contact, or two contiguous parts of a single object. And based on Newton´s 3rd Motion Law.
So, before any further comment on what said by puppy power in #156, "the centrifugal force associated with the electrons of atoms" (what justifies to say that?), I´m going to go beyond what I said in #154, in order to show (once more) that real centrifugal forces do exist.
The example in #154 about the vertically hanging steel cylindrical bar tried to put cristal clear how 2nd and 3rd Newton´s Laws (certainly thanks to inertia) make two opposite, vertical tensile forces be exerted on each side of any bar section.
Let us now suppose the bar rotating (at constant angular speed), in a horizontal plain, around its C.G.
If we imagine the bar vertically cut in slices, we can deduce that as each slice has to have a centripetal acceleration, contiguous slices have to exert forces to cause that acceleration.
Slices at their extremes ("A" slices) only have one contiguos slice each (B slices). B has to exert an inward force on A, equal to ω˛r times its mass. Then, A exerts same but outward force on B (Newton´s 3rd Law). THAT is a real centrifugal force !
B slice has ω˛r acceleration, with a little smaller "r". As it is being pulled outward by A, C slice has to pull inwards B with a force bigger than that in a quantity equal to ω˛r (its smaller "r") times its mass. Then, B exerts same but outward force on C: ALSO a real centrifugal force ...
We could continue that way up to the bar C.G.
All slices are being stretched due to those centripetal and centrifugal forces, both equally REAL.
Similarly, if e.g. an athlete in a circus is somehow made rotate hanging from his hands (even not horizontally, just with some inclination), he does feel centrifugal forces, but no just as a "tendency" to move along the tangent due to inertia. He actually feels his body is being stretched due to REAL forces, centripetal and centrifugal.
Title: Re: What is centrifugal force?
Post by: PmbPhy on 28/10/2017 06:55:07
What is centrifugal force?
I'm a late comer to this rather long thread so some of what I'm going to say might have already been mentioned.

The centrifugal force is an inertial force which means that it can only exists within non-inertial frames of reference. That is to say that the centrifugal is that force which appears due to the observer being in a non-inertial (i.e. accelerating) frame of reference. Another kind of inertial force is the Coriolis force. And the most important type of inertial force in general relativity is the gravitational force. This can be a bit confusing when explained in a short post so a long time ago I created a web page which defines and describes inertial forces. If you'd like to read it then its at

http://www.newenglandphysics.org/physics_world/gr/inertial_force.htm

There is a passage in there which comes from an article that Einstein wrote on general relativity where he explains why we should think of inertial forces as "real" forces. He specifically talks about the centrifugal force. There are three other textbook quotes from texts currently being used which say the same thing. They're "modern" textbooks if we understand "modern" to mean that the topic being discussed is on the theories currently being taught. It doesn't mean that they were written within the last 5 years. Lol!
Title: Re: What is centrifugal force?
Post by: rmolnav on 28/10/2017 12:14:00
I'm a late comer to this rather long thread so some of what I'm going to say might have already been mentioned.
You have forgotten you sent posts long ago ... I remember your user´s name, and have seen your first post was in 24/8/2016, where you logically (?) said something similar:
"Simply put, centrifugal force is an inertial force. If you're at rest in a rotating frame of reference then objects which are moving with no acceleration in the inertial frame will accelerate in your frame"
I posted tens of examples similar to recent ones, always trying to find clearer cases to refute that restrictive definition of centrifugal force (and other errors)
If, e.g., you have read my last post, you must have seen each imaginary slice exerts an outward force on inner contiguous one, as direct consequence of Newton´s 2nd and 3rd Laws ... Aren´t those forces real "centrifugal" forces (forces in the sense "fleeing" from a center), WHATEVER the reference frame ??
In that post you referred to accelerations ("...objects which are moving with no acceleration in the inertial frame will accelerate in your frame"). That is quite clear... It´s similar to what happens, e.g., when pilots of two sailing ships, each with its own course and speed, look at each other ... We have what is called "relative course" ... What you see is the result of deducing your own vector velocity from the other´s ...
But I consider that to extend that idea of moving reference frames to forces is rather erroneous, or at least it can lead to confusion.   
I´m going to bring up another example, not mentioned before as far as I can remember.
Imagine a fun ground whip, where we all enjoyed when children. Let us put a weight between two springs, already a little stretched, forming a horizontal radial line with one extreme fixed to the closed handle bar, and the other to the seat back.
When the cart (?) at most bent part of its trajectory, inner spring will be clearly stretched much more ... If it were a spring scale it would show the increase of forces acting on its hooks. The weight would be exerting an outward force on outer scale hook, that is a real CENTRIFUGAL force (scales don´t gage only "apparent" or "fictitious" forces)
And that would be a fact, whatever it were observed by somebody standing still outside the installation, or by somebody inside the cart and experiencing same accelerations as the weight ...
 
Title: Re: What is centrifugal force?
Post by: rmolnav on 06/11/2017 12:27:04
In several threads, about object dynamics: gravity, tides, centrifugal forces, Newton´s Laws …, I´ve long been showing my stand.
I got some replies, but almost none agreeing with me clearly … I don´t actually know the stand of most readers about “my" ideas ...
There is a detail it would be very interesting for me to receive more comments about, before going any further with other consequences of the issue I have in mind and I´m planing to send. In order to have a cleaner ground to play on …
It´s the question of how we (and somehow objects) feel gravity.
If we (or an object) are pulled by a massive object, and nothing else prevent us to accelerate what required by Newton´s 2nd Law, internal stresses are almost negligible: as if with no gravity, either still or with constant velocity vector.
But if a 3rd object don´t let us move with required 2nd Law acceleration, exerting on us another force, Newton´s 3rd Law “turns up” and we feel internal stresses. THOSE stresses are what actually “tell” us we are in a gravity field (whatever the deep explanation of gravity), NOT GRAVITY itself.
If we are standing, mainly feet and legs compression. If sitting, our bottom compression (especially if a hard seat !!). If in bed, smaller compression along our body. If hanging from our hands and arms, we feel strong tensile stresses there …
And if only part of the theoretically required “g” is allowed to happen, above mentioned stresses will be smaller, proportionally to “not allowed” acceleration … I mean, if e.g. a skyscraper lift fell with g/3 acceleration, and we were standing on its floor, at our feet and legs (and rest of our body) we would feel 2/3 of the compression stresses we were feeling when no movement (or with constant speed movement)
Title: Re: What is centrifugal force?
Post by: hamdani yusuf on 07/11/2017 01:23:28
It´s the question of how we (and somehow objects) feel gravity.If we (or an object) are pulled by a massive object, and nothing else prevent us to accelerate what required by Newton´s 2nd Law, internal stresses are almost negligible: as if with no gravity, either still or with constant velocity vector.But if a 3rd object don´t let us move with required 2nd Law acceleration, exerting on us another force, Newton´s 3rd Law “turns up” and we feel internal stresses. THOSE stresses are what actually “tell” us we are in a gravity field (whatever the deep explanation of gravity), NOT GRAVITY itself.
We can see astronauts in ISS don’t feel gravity even though the gravitational fields there are still high (almost 90% of gravity on earth surface). That’s because the station is in free fall.
The internal stresses are caused by difference of force vectors working on different body parts. Let’s compare the feelings of ISS astronauts with divers, sky divers, or someone doing indoor skydiving, or levitated frog in a strong magnetic field.
I think we can still find out that we are in a gravity field even when we don’t feel the stresses, by calculating the apparent movement of distant stars.

Title: Re: What is centrifugal force?
Post by: rmolnav on 07/11/2017 08:33:05
We can see astronauts in ISS don’t feel gravity even though the gravitational fields there are still high (almost 90% of gravity on earth surface). That’s because the station is in free fall.
Thank you.
I would rather say "That’s because THEY are in free fall" ... I know you also mean that, but I kind of flee from expressions which seem to refer to the reference frames, as unique reason of what happens ...
Apart from that, I insist: they don´t actually feel gravity, because gravity itself can´t be felt. We feel internal stresses, that appears when not all parts of our body are allowed to fall "100% free",
The internal stresses are caused by difference of force vectors working on different body parts.
Yes. But those vectors are not only Earth´s gravity pull vectors on different body parts ...
I´ve already commented this in many different cases: as our body is "obliged" to move as a whole, and its parts are not equally far away from Earth´s C.G., on the one hand gravity pull per unit of mass varies from part to part, especially if we are in a "radial" position. The farther, the smaller. And on the other hand, required centripetal acceleration for actual rotation (ω˛r), varies too. The farther the bigger.
That´s why our farther parts, not being sufficiently attracted by Earth to rotate at ω angular speed, have to be additionally pulled by inner contiguous parts ... That also causes pulls from outer parts on inner contiguos ones, in the opposite sense (Newton´s 3rd Law) (by the way, those last pulls are real centrifugal forces ...).
All those internal stresses, apart from stretching (in this case) our bodies, are the FACTS that we actually feel (whatever the frame of reference), NOT gravity itself. And not only in this particular case.
That "idea" is what I do want to convey, both in my last post and in this one.   
Title: Re: What is centrifugal force?
Post by: rmolnav on 07/11/2017 11:42:42
Let’s compare the feelings of ISS astronauts with divers, sky divers, or someone doing indoor skydiving, or levitated frog in a strong magnetic field.
Also in those cases what I say applies.
Internal stresses felt by astronauts are very, very small, and distributed across their bodies.
When on Earth much bigger additional forces, pushing or pulling, have to be exerted on our bodies by other external objects, to keep us somehow rotating at zero altitude. Newton´s 3rd Law implies we exert opposite forces on those objects ...
Each part of our body can have only the required centripetal acceleration at zero altitude (apart from sky divers case). As also Newton´s 2nd Law applies for each body part (due to same reasons as what said when in ISS) internal stresses occur, in each case depending on the way external forces are exerted on us ...
As in all those cases external forces are applied distributed over big areas of our bodies, in no body part internal stresses accumulate significantly, as if if we were "floating"  ... But they do occur.
As I previously said, in all cases what is felt is NOT GRAVITY itself, but those internal stresses. And they will be proportional to the fraction of Earth´s attraction which is not "allowed" to cause any actual acceleration, centripetal for the rotation, or linear if any (e.g. sky divers).
Title: Re: What is centrifugal force?
Post by: rmolnav on 21/12/2017 18:39:56
In an e-mail discussion with a scientist from NOAA, after some comments I sent him in relation to a publication from them I had seen on the internet (that resulted rather old), he told me literally:
"It used terminology of science and forces which were common in the 1950s.  Such as centrifugal force.  Centrifugal force was always an "imaginary force" (not a real / measurable force).  But that type of description made the concepts easier to understand and explain.  That  description and use of centrifugal force continued to be common practice until the 1970-80's.  At that point, the terminology shifted and the textbooks used in grade schools were changed to use a more modern terminology and description of this "effect" being a result of inertia rather than an "imaginary force"."
I would add that, if correctly considered applied NOT to the object following a curved path, but to the other object which produces the centripetal acceleration of the former, what he calls "this effect", not an "imaginary force" as he says, is quite a REAL force (certainly due to inertia, clearly expressed by Newton in his 3rd Law of Motion) ... The same I´ve always been saying here, since my #28 of 2/10/2016 !!
By the way, I suggest you to have a look at:
https://www.thenakedscientists.com/forum/index.php?topic=49715.new
Recently comments directly connected to centrifugal forces have been posted there ...
Allow me say I consider them very interesting, though I myself sent them ...
Title: Re: What is centrifugal force?
Post by: alancalverd on 21/12/2017 21:13:46
Back to the elementary "whirling rock on a string". There is nothing imaginary about the tension in the string. You can calculate it, and measure it, and the moment you cut or release the string so the rock is no longer following a curved path, it disappears. So centrifugal force is the force exerted by the rock on the string.It is the force that makes a rubber tyre expand radially, and shatters an overspeeding grindstone.

Imaginary forces do not break real objects.
Title: Re: What is centrifugal force?
Post by: rmolnav on 22/12/2017 13:46:43
Back to the elementary "whirling rock on a string". There is nothing imaginary about the tension in the string.
You are right, and I´ve posted tens of similar examples saying the same.
But it is not that simple when there is no physical link.
E.g.: Earth follows its elliptical orbit thanks to the pull from the Sun: centripetal force.
Newton´s 3rd Law: Earth exert an equal (but opposite) pull on the Sun ...
What real force could be called centrifugal force? ...
Title: Re: What is centrifugal force?
Post by: rmolnav on 02/05/2018 11:34:43
Some months ago I interchanged a few emails with a NOAA scientist, discussing some details I previously saw on a publication of them about tides which I was not completely in agreement.
Recently I´ve been talking about that in:
https://www.thenakedscientists.com/forum/index.php?topic=49715.new#lastPost
where tides, and CENTRIFUGAL FORCES as something directly related to tides, have been  long discussed by some of thenakedscientist members …
What follows is one of the first things mentioned NOAA scientist told me:
"The publication you are referring to is "Our Restless Tides", a 10-page pamphlet developed in the 1950's to provide a basic description of the forces which create the tides.  It's intended audience were the grade school children and adults of that time.  It used terminology of science and forces which were common in the 1950s.  Such as centrifugal force.  Centrifugal force was always an "imaginary force" (not a real / measurable force).  But that type of description made the concepts easier to understand and explain.  That  description and use of centrifugal force continued to be common practice until the 1970-80's.  At that point, the terminology shifted and the textbooks used in grade schools were changed to use a more modern terminology and description of this "effect" being a result of inertia rather than an "imaginary force”.”
I added in my last post:
RESULT OF INERTIA ... I do agree: Newton´s Motion Laws come from inertia !!
"THIS EFFECT" ... Centrifugal forces, in the cases when they are REAL, are not just an "effect" or tendency due to inertia ... Affected objects "tend" to keep their velocity vector due to their inertia, and centrifugal FORCE is derived from inertia, but it is something more than that "effect" ...
Title: Re: What is centrifugal force?
Post by: alancalverd on 02/05/2018 12:53:10
Centrifugal force was always an "imaginary force" (not a real / measurable force).
So what is providing the measured tension in the string? What is making the real blood measurably separate in what I now have to call the Imaginary Centrifuge in my Virtual Laboratory? What is pulling on my arms and legs when I make a 60-degree banked turn in the plane? What caused the radial expansion of the tyres on my racing car?

Inertia? No way. Inertia is proportional to mass, and there's no mechanism for converting circular motion into mass.
Title: Re: What is centrifugal force?
Post by: PmbPhy on 02/05/2018 15:59:45
Quote from: alancalverd
What is making the real blood measurably separate in what I now have to call the Imaginary Centrifuge in my Virtual Laboratory? What is pulling on my arms and legs when I make a 60-degree banked turn in the plane? What caused the radial expansion of the tyres on my racing car?
Its known in GR circles as Inertial Induction. See Peacocks book Cosmological Physics page 6.
Einstein said it was a gravitational force which is produced when the field of reference changed from an inertial frame to a non-inertial frame. The centrifugal force is an inertial force since its directly proportional to inertial mass.

As far as what Einstein actually said. From my website at
http://www.newenglandphysics.org/physics_world/gr/inertial_force.htm

Albert Einstein - That the relation of gravity to inertia was the motivation for general relativity is expressed in an article Einstein wrote which appeared in the February 17, 1921 issue of Nature
Quote
Can gravitation and inertia be identical? This question leads directly to the General Theory of Relativity. Is it not possible for me to regard the earth as free from rotation, if I conceive of the centrifugal force, which acts on all bodies at rest relatively to the earth, as being a "real" gravitational field of gravitation, or part of such a field? If this idea can be carried out, then we shall have proved in very truth the identity of gravitation and inertia. For the same property which is regarded as inertia from the point of view of a system not taking part of the rotation can be interpreted as gravitation when considered with respect to a system that shares this rotation. According to Newton, this interpretation is impossible, because in Newton's theory there is no "real" field of the "Coriolis-field" type. But perhaps Newton's law of field could be replaced by another that fits in with the field which holds with respect to a "rotating" system of co-ordinates? My conviction of the identity of inertial and gravitational mass aroused within me the feeling of absolute confidence in the correctness of this interpretation.

[quoter]
Inertia? No way. Inertia is proportional to mass, and there's no mechanism for converting circular motion into mass.
[/quote]
Prove it. :)
Title: Re: What is centrifugal force?
Post by: alancalverd on 02/05/2018 17:40:03
Quote
Inertia? No way. Inertia is proportional to mass, and there's no mechanism for converting circular motion into mass.
Prove it.

Wirth pleasure, my friend.

Circular motion is defined by angular velocity r. ds/dt  with dimensions [L]2[T]-1. Mass either has dimension [M] or energy equivalent E/c2 which unsurprisingly also has dimension [M].

The fact remains that you can't claim a force that anyone can measure, to be "imaginary and unmeasurable". And if it acts away from the center of revolution (why else would the tyre fall off the wheel?) then it's etymologically justifiable to call it centrifugal.

Start with an object moving in a straight line.If you want to make it move in an arc, you must apply a centripetal force perpendicular to its momentum vector (Newton number 1!). Therefore the object will apply an equal and opposite centrifugal force to whatever is applying the centripetal force (Newton number 3!)
Title: Re: What is centrifugal force?
Post by: rmolnav on 02/05/2018 19:07:32
So what is providing the measured tension in the string? What is making the real blood measurably separate in what I now have to call the Imaginary Centrifuge in my Virtual Laboratory? What is pulling on my arms and legs when I make a 60-degree banked turn in the plane? What caused the radial expansion of the tyres on my racing car?
Inertia? No way. Inertia is proportional to mass, and there's no mechanism for converting circular motion into mass.
I do regret you seem not to have read, or to have forgotten, the so many posts I started to send here as early as one and a half year ago, #28 ... I´ve given many examples in line with the first paragraph of what quoted.
And regarding second paragraph, I´m afraid you are not keeping in mind that, what you yourself said afterwards:
Start with an object moving in a straight line.If you want to make it move in an arc, you must apply a centripetal force perpendicular to its momentum vector (Newton number 1!). Therefore the object will apply an equal and opposite centrifugal force to whatever is applying the centripetal force (Newton number 3!)
,
something I´ve already said many, many times, wouldn´t be possible without the physical phenomenon of INERTIA ... Newton puts that phenomenon in physical terms (force, mass and acceleration).
And 3rd one shows objects are kind of "stubborn", as they "think":" I want to keep keep my velocity vector (INERTIA) ... If any other object tries to "force" me and change it, I´ll exert back an equal force on it, trying to continue with my speed ..."
Excuse me for the joke, but it reflects reality.
And please kindly note what quoted by you from my post:
Quote from: rmolnav on Today at 11:34:43
Centrifugal force was always an "imaginary force" (not a real / measurable force).
was not said by me, but by the NASA scientist I had mentioned.
And he says "IT WAS ...", showing the big confusion about the concept that was, though perhaps not "always", so common decades ago, and even today according to my recent year experience.
Well, I have to leave it now.
Tomorrow, more quietly, I´ll say something more, and reply to PmbPhy too.
Title: Re: What is centrifugal force?
Post by: chiralSPO on 02/05/2018 20:23:12
Without making any claims myself, I will simply leave this here:

 [ Invalid Attachment ]

https://xkcd.com/123/
Title: Re: What is centrifugal force?
Post by: rmolnav on 03/05/2018 07:56:14
Without making any claims myself, I will simply leave this here: ... (with three animated pictures)
Not bad way to show existing confusion... Even the author himself is confused: the introduction of a "rotating system" of reference, a mathematical "trick" not always justified, requires the concept of a centrifugal f. actually "fictitious", but applied to same considered rotating object ... Nothing to do with 3rd Newton´s Motion Law, because REAL centrifugal "reaction" force is exerted by the rotating object, on ANOTHER object: the one exerting the centripetal force required for the rotation of the former !!
THERE is where main cause of existing confusion resides, as I´ve been saying here (and in many, many other sites) since my very first post #28, 17 months ago !! Sadly, to no or little avail !!
Title: Re: What is centrifugal force?
Post by: rmolnav on 03/05/2018 08:23:04
Einstein said it was a gravitational force which is produced when the field of reference changed from an inertial frame to a non-inertial frame. The centrifugal force is an inertial force since its directly proportional to inertial mass.
I´m afraid there is too much confusion out there, even strictly within Newton´s Mechanics, to try an understanding beyond its limits, e.g. Einstein´s theories ...
Whatever the deep nature of inertia and gravity could be, Newton´s Mechanics is quite valid in most of usual cases.
Let me to suggest you to have a look to my post here six months ago, #159 (#160 too), replying #158 (yours)
Title: Re: What is centrifugal force?
Post by: rmolnav on 03/05/2018 08:36:57
... there is too much confusion out there ...
As a prove of that, please have a look to my last mail of several I sent to an "edu" well considered site (in 2016):
"Thank you VERY MUCH for your ideas. But you know, it is not that I want to apply "centrifugal" to a broader scenario. At least in Spanish, and in other latin origin languages, "centrifugal" does not need any definition: with its two parts "centri" and "fugal", you can tell its meaning. In English you also have "fugitive", from same origin, but perhaps it is not so self-evident. It´s fanny that in Spanish the "primary" force, centripetal, does have to be defined, because its part "petal", surely from latin too, does not tell us anything … I can´t remember any other similar common word! (though there must be some).
A more restrictive definition (back to centrifugal) could be useful to Physicists, but the term is something of everyday life, and it wouldn´t be sufficient to avoid confusion.
Many people, even from education institutions, seem to consider that term a kind of forbidden word, and they give erroneous explanations trying to specify the physical causes of phenomena which need a real centrifugal (or whatever we wanted to call it) force to be correctly understood.
Just to give you an example, what follows trying to answer the question "Would I weigh less at the Equator?":
"Earth has a bulge at the equator created by the planet’s rotation and a moving body’s tendency to continue in a straight line. (Sometimes this is misleadingly called "centrifugal force", but it's really just Newton’s laws of motion.) While standing at the equator you are further away from the bulk of Earth’s mass than at the poles, so the planet exerts less pull on you."
By the way, apart from de definition you gave me, I´ve seen others from important editors:
"Centrifugal force, a fictitious force, peculiar to a particle moving on a circular path, that has the same magnitude and dimensions as the force that keeps the particle on its circular path (the centripetal force) but points in the opposite direction" (which object does it affect? …)
"In physics, centrifugal force is the force that makes objects move outwards when they are spinning around something or travelling in a curve (??!!)
"Newton's third law states that for every acting force there is an equal and opposite reaction force.
Therefore there must be an equal and opposite reaction force to the Centripetal Force: the Centrifugal Force" (not mentioning the two objects of Newton´s law >>confusion) !!)
I MUST SAY I CAN´T UNDERSTAND WHY IT WOULD BE BETTER TO RESERVE A TERM FOR A FICTICIOUS FORCE RATHER THAN USING IT FOR THE REAL ONE, WHICH BESIDES, IT IS PRESENT IN MANY SCENARIOS ALL ACROSS THE UNIVERSE".

 
Title: Re: What is centrifugal force?
Post by: alancalverd on 03/05/2018 11:03:36
So would someone please tell me the preferred name of the magic that separates cream from milk, platelets from plasma, and heavy ions from light ones, in the various bits of everyday kit we use to do these useful things? If the force is imaginary, why does the g meter in my aeroplane (and the passengers' drinks) succumb to the same illusion as me and all my passengers?

Title: Re: What is centrifugal force?
Post by: rmolnav on 03/05/2018 12:01:47
So would someone please tell me the preferred name of the magic that separates cream from milk, platelets from plasma, and heavy ions from light ones, in the various bits of everyday kit we use to do these useful things? If the force is imaginary, why does the g meter in my aeroplane (and the passengers' drinks) succumb to the same illusion as me and all my passengers?
I can´t understand why you keep asking that, as if WE ALL were saying "the force is imaginary" ...
I´ve said quite a lot of times the opposite, BUT that idea is very, very spread ... Have you really read at least my last post, especially what at the end in capital letters???
Another example of the enormeous confusion (and my fight against it). What follows is an email I sent in november 2016:
"On your site:
https://global.britannica.com/science/centrifugal-force
(THE VERY BRITANNICA !!!)
it is said:
"Although it is not a real force according to Newton’s laws …"
Sorry, but I found that erroneous. REAL centrifugal forces frequently produce quite real effects …
E.g. when an athlete is rotating a hammer to be thrown, the wire is pulling the hammer (centripetal f. which produces the centripetal acceleration required for the rotation). And according to 3rd Newton´s Law, correctly applied, the hammer is also pulling outwards THE WIRE extreme.
That is quite REAL force, and CENTRIFUGAL. Should we have put a spring dynamometer between wire and hammer, we could have gauged that force …
The spring of the dynamometer requires two REAL forces applied to its opposite hooks to get stretched and show any figure”.
As you can see in linked site, they also say:
"A stone whirling in a horizontal plane on the end of a string ...
If the stone is moving at a constant speed and gravity is neglected, the inward-pointing string tension is the only force acting on the stone. If the string breaks, the stone, because of inertia, will keep on going in a straight line tangent to its previous circular path; it does not move in the outward direction as it would if the centrifugal force were real “ (!!!)
In a word: UNBELIVABLE …
And I could give tens of similar examples.
And, logically, if laymen read that, any effort to convey the actual physical reality is useless !!!
Title: Re: What is centrifugal force?
Post by: rmolnav on 05/05/2018 11:35:59
... there is too much confusion out there ...
As a prove of that, please have a look to my last mail of several I sent to an "edu" well considered site (in 2016)
For anybody who could be interested in having more "food for thought", what follows is my first mail to them, where there is also a link to mentioned site:
"On 
http://math.ucr.edu/home/baez/physics/General/Centrifugal/centri.html
it is said:
"Centrifugal force was invented to allow us to …"
I WOULD RATHER say it is NOT an invention, but something quite real. It is present in many real phenomena.
E.g.  when an athlete is rotating a hammer to be thrown, the wire is pulling the hammer (centripetal f. which produces the centripetal acceleration required for the rotation). And according to 3rd Newton´s Law, correctly applied, the hammer is also pulling outwards THE WIRE extreme.
That is quite REAL force, and CENTRIFUGAL. Should we have put a spring dynamometer between wire and hammer, we could have gauged that force …
The spring of the dynamometer requires two REAL forces applied to its opposite hooks to get stretched and show any figure"
THEN I WAS SENT WHAT FOLLOWS:
"Centrifugal force is, by definition, a force that appears in a rotating frame.  That's its definition.  The athlete you describe is in a non-rotating frame, if we neglect Earth's rotation.  He pulls on the hammer as he spins the hammer around him, and this pulling force manifests as a tension in his arm.  It produces the centripetal acceleration of the hammer around the athlete. 
The hammer certainly pulls on his arm with the same force, and this could certainly be
measured by a spring device.  But that force is not a centrifugal force, because it is not something that is being described in a rotating frame (???, this is mine)
If you were a miniature creature riding on the hammer, you -would- be in a rotating frame, and then you would certainly say that a centrifugal force was present: this force would be trying to pull you away from the hammer--you'd have to hold on tight to the hammer to counteract this force that you felt.  But someone in an inertial frame says that the force you feel is not present in the inertial frame, and it is certainly not needed to apply Newton's laws to the situation in the inertial frame. Rather, it's due to the fact that the hammer is being pulled away from you by the athlete, which thus requires you to hold on to the hammer.  When you need to hold on, you interpret that as the result of a force that's pulling you away from the hammer.  But nothing physical is pulling you away from the hammer.  The hammer is being pulled away from you by the athlete--in the inertial frame".
I INSIST: all that artificial "tricky" tool of inertial and non inertial frames of reference, and wherever things such as "Centrifugal force is, by definition, a force that appears in a rotating frame. That's its definition" are said, should not be considered as kind of a Bible. Perhaps there should be a clear "User´s Manual", were it possible, to try an avoid confusion, or at least diminish its likelihood ...
Title: Re: What is centrifugal force?
Post by: rmolnav on 07/05/2018 11:01:05
THEN I WAS SENT WHAT FOLLOWS:
More "food for thought". After that really confusing "story" I was told, I replied:
"Hello Don,
You say:
"Centrifugal force is, by definition, a force that appears in a rotating frame.  That's its definition".
I consider that expression should not be defined such a narrow way. Everybody knows the adjective "centrifugal" implies some kind of  "fleeing from a center" …  According to Oxford Advanced Leaners Dictionary (7th Edition), "Moving or tending to move away from a center". And different types of forces can match that definition.
We could diminish confusion clearly specifying which force type are we talking about, rather than restricting its scope.
As it seems hammer throwing case interested you, please kindly have a look at what follows. Not long ago I sent it to a blog discussing the issue:

" Differences between the case of two celestial objects rotating around their barycenter, and the case when an object is being rotated by us by means of a cord o similar tool (as e.g. in hammer throwing), go beyond the “physical” difference that nothing connects the celestial objects to each other, apart from the “tele-connection" of gravity …
Somehow the celestial objects were initially given their speeds very long ago, and no energy is transferred now from/to each other.
When an athlete initiates hammer rotation, he has to transfer energy to the hammer, in order to increase its tangential speed the more the better.
For the sake of simplicity, i consider a rotation always around a vertical axis. The “tension” of the wire, I mean the inward force, is not strictly “centripetal”. It has three components:
One vertical, which has to support hammer weight (the wire can´t be completely horizontal).
Another horizontal and centripetal, which produces the centripetal acceleration necessary for the hammer to follow its circular path.
And yet another horizontal but tangential, the usually “forgotten” force. It is due to the fact that athlete hands are also rotating, but the straight line hands-wire-hammer is not a radius of hammer trajectory … The athlete tries and increases the angular speed of his hands, with the purpose of increasing angular and tangential speeds of the hammer, before releasing it. There is a sort of angular “delay” of the hammer relative to the situation of athlete hands. That´s the cause of the tangential component of wire tension.
So, the athlete increases more and more wire tension, and both its centripetal and tangential components increases too. Centrifugal force (opposite to centripetal one: the hammer pulling outwards wire end) increases as the centripetal one does… That outward, centrifugal force that increases more and more, could appear to cause the hammer to “fly” when the athlete releases it. But IT NOT DOESN´T.  The cause is actually mentioned tangential component of wire tension, that increases velocity revolution after revolution, with continuous transference of energy from the athlete to the hammer … As soon as the wire is released, hammer (+ wire) is “free” and go straight at its acquired tangential velocity (apart from weight and air friction effects).
After all, the centrifugal force was NOT being exerted on the hammer, and even if it had been, it would require time to increase any velocity, but it “dies” at same instant the hammer is released.
So, we can say centrifugal force rol is “important: the wire could not exert any centripetal force on the hammer not being tight, and it could not be tight acting only a force at one of its extremes !!
And don´t forget that, as I´ve been referring to during last weeks, centrifugal forces have other important roles in other cases. I have to decide which case may be worth to insist on."
Any further comments?
Yours ..."
Title: Re: What is centrifugal force?
Post by: rmolnav on 10/05/2018 12:13:33
LAST CHAPTER  of the "story" ...
Then I got following answer:
"> Everybody knows the adjective "centrifugal" implies some kind of "fleeing from a center" (quoted from my previous mail)
Sure, and that's how the word is used in physics, to denote the fact that we notice things trying to fly outwards when we are in a rotating frame.  Newton's laws don't hold in non-inertial frames, so when something accelerates in a rotating frame, we are not obliged to say that this acceleration was produced by a force.  But if we insist on doing so, then we call the force centrifugal.
The force that a hammer exerts on the thrower is something we speak of in the thrower's frame, which is being taken as inertial for the sake of argument here.  It's a real force, unlike the one that we invent in the rotating frame if we want to apply Newton's laws there.  If we called the force produced by the hammer a centrifugal force, there would be a confusion about which frame we were discussing: inertial or non-inertial.  We just reserve the word "centrifugal" for rotating frames.
The force of the hammer on the thrower in the inertial frame is like the force of the ground on you or me; it's typically called a reaction force, but it doesn't get a more special name than that because it doesn't need one.  It's just the force that Newton's Third Law says is there.  You want to apply the word "centrifugal" to this scenario too, but like any word, if the meaning we give to it is too broadly applicable, it loses its value in any quantitative discussion.
Reserving that word for rotating frames only makes it more useful.
There's a big, big difference between a real force of tension and a force that we invoke in a rotating frame to make Newton's laws work outside their normal region of validity.  We signal that big difference by giving the latter invoked force the special name of "centrifugal".  Sure, it's a question of how such words are defined, but as I said, giving a word a wide meaning reduces its usefulness in quantitative discussions".
AND THEN I sent him what I posted here a week ago (#175).
Title: Re: What is centrifugal force?
Post by: rmolnav on 25/05/2018 12:18:45
Some of you, if has followed my posts with certain interest, surely has seen I´m not too keen on that  inertial and non-inertial system of reference mathematical "trick", when used to state that centrifugal force is not a real force, that is ficticious ...
Recently, when posting here several pieces of email I interchanged with the people from:
http://math.ucr.edu/home/baez/physics/General/Centrifugal/centri.html,
after seeing the bizarre explanations given by them, I showed my stand and said (#178):
"I INSIST: all that artificial "tricky" tool of inertial and non inertial frames of reference, and wherever things such as "Centrifugal force is, by definition, a force that appears in a rotating frame. That's its definition" are said, should not be considered as kind of a bible. Perhaps there should be a clear "User´s Manual", were it possible, to try an avoid confusion, or at least diminish its likelihood … "
I had previously refuted those type of ideas, e.g. on #159:
"In that post you referred to accelerations ("...objects which are moving with no acceleration in the inertial frame will accelerate in your frame"). That is quite clear... It´s similar to what happens, e.g., when pilots of two sailing ships, each with its own course and speed, look at each other ... We have what is called "relative course" ... What you see is the result of deducting your own vector velocity from the other´s ...
But I consider that to extend that idea of moving reference frames to forces is rather erroneous, or at least it can lead to confusion.   
I´m going to bring up another example, not mentioned before as far as I can remember.
Imagine a fun ground whip, where we all enjoyed when children. Let us put a weight between two springs, already a little stretched, forming a horizontal radial line with one extreme fixed to the closed handle bar, and the other to the seat back.
When the cart (?) at most bent part of its trajectory, inner spring will be clearly stretched much more ... If it were a spring scale it would show the increase of forces acting on its hooks. The weight would be exerting an outward force on outer scale hook, that is a REAL centrifugal force (scales don´t gauge only "apparent" or "fictitious" forces !!)
And that would be a fact, whatever it were observed by somebody standing still outside the installation, or by somebody inside the cart and experiencing same accelerations as the weight ..."
Yesterday, ruminating rather unwillingly on the issue, I had a kind of EUREKA moment, and I think I saw the actual root cause of existing confusion caused by that "tricky" mathematical tool.
I´ll draft another post carefully, in order to do my best trying to unveil the idea as clearly as possible ... It´s a kind of philosophical reasoning, rather than only physical, and I didn´t wish it could be to no avail (if I were not able to convey my idea), as so many times has happened !!
Title: Re: What is centrifugal force?
Post by: rmolnav on 25/05/2018 18:40:36
I´ll draft another post carefully, in order to ...
Preparing that, i´ve entered Wikipedia, initially looking for frames of reference, and there is a link to centrifugal force, where I´ve rarely entered, and I decided to have a look at.
They use the so common definition:
"In Newtonian mechanics, the centrifugal force is an inertial force (also called a "fictitious" or "pseudo" force) directed away from the axis of rotation that appears to act on all objects when viewed in a rotating frame of reference".
BUT further down one can read:
"Within this view of physics (?), any other phenomenon that is usually attributed to centrifugal force can be used to identify absolute rotation. For example, the oblateness of a sphere of freely flowing material is often explained in terms of centrifugal force. The oblate spheroidshape reflects, following Clairaut's theorem, the balance between containment by gravitational attraction and dispersal by centrifugal force. That the Earth is itself an oblate spheroid, bulging at the equator where the radial distance and hence the centrifugal force is larger, is taken as one of the evidences for its absolute rotation".
Could that "dispersal by centrifugal force", if this c.f. depended on the type of frame of reference, and were "ficticious" if in relation to a non-inertial frame of reference, have caused the oblateness of our planet, being the so called equatorial bulge higher than 40 km ??
We have to keep in mind that Earth oblateness is not only as far as oceans are concerned, it also affect solid Earth.
Curiously, Earth´s mountain peaks farthest from its C.G. are not in the Himalayas (e.g. the Everest), but in Peruvian Andes, precisely due to billions of year action of centrifugal forces (logically, quite REAL).
Title: Re: What is centrifugal force?
Post by: PmbPhy on 25/05/2018 21:16:54
The centrifugal force is an inertial force. For details on such forces see
http://www.newenglandphysics.org/physics_world/gr/inertial_force.htm

In particular, the centrifugal force is an inertial force which is observed in rotating (non-inertial) frames.

I has nothing to do with things on a string in an inertial frame. Inertial forces were important to Einstein when he was creating general relativity. In the February 17, 1921 issue of Nature Einstein wrote
Quote
Can gravitation and inertia be identical? This question leads directly to the General Theory of Relativity. Is it not possible for me to regard the earth as free from rotation, if I conceive of the centrifugal force, which acts on all bodies at rest relatively to the earth, as being a "real" gravitational field of gravitation, or part of such a field? If this idea can be carried out, then we shall have proved in very truth the identity of gravitation and inertia. For the same property which is regarded as inertia from the point of view of a system not taking part of the rotation can be interpreted as gravitation when considered with respect to a system that shares this rotation. According to Newton, this interpretation is impossible, because in Newton's theory there is no "real" field of the "Coriolis-field" type. But perhaps Newton's law of field could be replaced by another that fits in with the field which holds with respect to a "rotating" system of co-ordinates? My conviction of the identity of inertial and gravitational mass aroused within me the feeling of absolute confidence in the correctness of this interpretation.
Title: Re: What is centrifugal force?
Post by: rmolnav on 26/05/2018 08:08:23
The centrifugal force is an inertial force. For details on such forces see
http://www.newenglandphysics.org/physics_world/gr/inertial_force.htm
In particular, the centrifugal force is an inertial force which is observed in rotating (non-inertial) frames.
I´m afraid that is rather confusing ... What do you mean with "... which is observed in ..."?
Does it mean it is a real force "observed" by us? Or, in that "particular" case, is it rather a kind of tricky tool WE apply to bring a "fictitious" situation (an accelerating frame of reference) back to reality (with all REAL effects which have disappeared in that frame of reference?
Apart from that, linked site states (according to Einstein):
"In general relativity inertial forces are identical in nature to gravitational forces" and defines:
"Inertial force: When the motion of the reference system generates a force (defined as the time rate of change of momentum, i.e. f ş dp/dt, which has to be, as measured in that system, we call that force an inertial force".
Therefore we could state:
"Centrifugal forces (as above defined) = inertial forces ("generated" ? by the reference system) = gravitational forces (acc. to Einstein)"
and, as far as I can understand, either both centrifugal and gravitational forces are REAL, or both are fictitious ...
Do you mean both are fictitious? ... Then, the question I posted yesterday (by the way, have you read it?):
"Could that "dispersal by centrifugal force", if this c.f. depended on the type of frame of reference, and were "ficticious" if in relation to a non-inertial frame of reference, have caused the oblateness of our planet, being the so called equatorial bulge higher than 40 km ??
would have an easy answer: that lifting of huge mountains is not the result of two opposite forces, but due to the distortion of space-time ...
But, whatever the deep nature of gravity and inertia, the phenomena considered by us can be explained within Newton´s Mechanics !!
Title: Re: What is centrifugal force?
Post by: PmbPhy on 30/05/2018 14:21:24
Quote from: rmolnav
I´m afraid that is rather confusing ... What do you mean with "... which is observed in ..."?
Sorry. I had no idea that would be confusing, .To "observe" means. Whenever you see a term you don't understand find a dictionary and look it up. In this case:
https://en.oxforddictionaries.com/definition/observation
Quote
The action or process of closely observing or monitoring something or someone. etc
To observer "in" means that you must be at rest in the non-inertial frame of reference. E.g. In the movie Mission to Mars and The Martian the astronauts can go to part of the ship which is rotating with respect to an inertial frame. An object in this part of the spaceship which has no force on it as observed in the inertial frame is accelerating in this rotating frame. Newton attributed that to using the wrong frame. Einstein came along and said there are no wrong frames. This acceleration as determined by observers in the rotating frame is said to be caused by the coriolis force which Einstein's general relativity views as a gravitational force. Einstein said it was a real force. I did post a URL to my website which makes all of this crystal clear. If people don't read what I have to say then I don't see a reason for saying it.
Title: Re: What is centrifugal force?
Post by: rmolnav on 31/05/2018 14:18:55
Quote from: rmolnav
I´m afraid that is rather confusing ... What do you mean with "... which is observed in ..."?
Sorry. I had no idea that would be confusing, .To "observe" means. Whenever you see a term you don't understand find a dictionary and look it up
Sorry, but my question was about what YOU mean when saying "... force which is observed in...", rather than what said on a dictionary … Because, as on Oxford dictionary:
"Observe: Notice or perceive (something) and register it as being significant", and
"Force: An influence tending to change the motion of a body or produce motion or stress in a stationary body".
One can "notice or perceive" directly a body and its motion, but  NOT something which is "an INFLUENCE tending to change the motion of a body or …"
To say which possible "influence" is the one you "notice or perceive" requires the intervention of not only your senses, but also your mind …
And your ideas could be right or wrong. Therefore one can´t actually "notice or perceive" a certain "influence" is the one "tending to change the motion of a body or produce motion or stress in a stationary body".
By the way, I also said:
"Does it mean it is a real force "observed" by us? Or, in that "particular" case, is it rather a kind of tricky tool WE apply to bring a "fictitious" situation (an accelerating frame of reference) back to reality (with all REAL effects which have disappeared in that frame of reference?"
Have you read that and consider it at least as a possibility? ...
I´m pretty sure many people misinterpret frame of reference issue, and draw wrong consequences.
As Einstein said, "there are no wrong frames" ... but what above said can and does happen !!
Title: Re: What is centrifugal force?
Post by: Vasyl on 19/11/2018 14:09:11
Can anyone explain an attached example of centrifugal force?
Title: Re: What is centrifugal force?
Post by: Halc on 19/11/2018 14:26:18
Can anyone explain an attached example of centrifugal force?
It labels F as centrifugal force, but the picture doesn't depict it.

The formula for centrifugal force (in a rotating frame) is mωr (where ω is angular velocity, labeled as L in the picture).  mv2/r is centripetal force, but in a rotating frame, v is zero, so that doesn't work.  In an inertial frame, there is no centrifugal force.
The F in the picture seems to depict a force being applied to the pulleys to apply tension in the belt.  It doesn't affect the speed of anything nor does it affect the forces being applied to m as it goes around.

Somehow the V in the picture is zero at the bottom and max at the top, which isn't what one would expect of a belt turning with constant linear speed at any point in the belt.

There is mention of acceleration, but it is unclear what is accelerating.
Title: Re: What is centrifugal force?
Post by: Vasyl on 19/11/2018 14:35:22
I mean that a centrifugal force can lift conveyors up if conveyors accelerate body on one side of tape and decelerate it on the other one. How is it possible? I can not understand my mistake.
Title: Re: What is centrifugal force?
Post by: Halc on 19/11/2018 14:53:49
I mean that a centrifugal force can lift conveyors up if conveyors accelerate body on one side of tape and decelerate it on the other one. How is it possible? I can not understand my mistake.
The body seems to be moving at constant speed in the picture.  Why would the tape be slowing when the weight is on one side and speeding up when the weight is on the other?  That is just not depicted in the picture.

Yes, the belt will tend to bow out its sides at high speeds, and that inertial effect is a function of the tension on the belt, the distance between the pulleys, and of course the speed of the belt.  If the belt speed is changing, it needs to be specified.  The picture suggests that the belt is stopped at the bottom and moving at the top, which makes no sense.  The entire belt needs to move at the same speed or the belt breaks.
Title: Re: What is centrifugal force?
Post by: Vasyl on 19/11/2018 16:41:00
The body seems to be moving at constant speed in the picture.  Why would the tape be slowing when the weight is on one side and speeding up when the weight is on the other?
A motor drives a tape and we can accelerate it or decelerate it. The topic is "is lifting force possible?"
Title: Re: What is centrifugal force?
Post by: Vasyl on 19/11/2018 16:47:39
The picture suggests that the belt is stopped at the bottom and moving at the top, which makes no sense.
There are arrows with lettering "acceleration", "deceleration". It means that we accelerate it from zero to max speed and decelerate it from max to zero.
Title: Re: What is centrifugal force?
Post by: Vasyl on 19/11/2018 16:54:46
The entire belt needs to move at the same speed or the belt breaks.
Yes, It does. You can even move a body at the same speed but with bigger wheel radius at the bottom and you will have the same result.
Title: Re: What is centrifugal force?
Post by: Halc on 19/11/2018 18:32:01
A motor drives a tape and we can accelerate it or decelerate it. The topic is "is lifting force possible?"
OK, the belt changes speed depending on where the mass is at the time.
The whole thing will vibrate nicely, but if you're asking if there is any net thrust to the entire system, the answer is no.  The center of gravity of the whole setup never moves, regardless of speed of any of the parts.

As for using a bigger wheel at one end and constant belt speed, that indeed makes no changes except that the weight isn't going to slow at one end or the other.  There will be no acceleration/deceleration since you specified constant belt speed.
Title: Re: What is centrifugal force?
Post by: Vasyl on 19/11/2018 19:30:11
The center of gravity of the whole setup never moves, regardless of speed of any of the parts.
Thanks a lot for your reply. I will try to understand it.
As for using a bigger wheel at one end and constant belt speed, that indeed makes no changes except that the weight isn't going to slow at one end or the other.  There will be no acceleration/deceleration since you specified constant belt speed.
I wanted to say that centrifugal force will be bigger on a top of conveyor and less at the bottom of it. After sum of two forces you have force in direction against gravity.
Title: Re: What is centrifugal force?
Post by: Halc on 19/11/2018 20:01:22
The topic is "is lifting force possible?"
The topic is "What is centrifugal force?".  There never was a mention of 'is lifting force possible", including on the diagram.  Of course lifting force is possible.  I lift things every day.
I think you're trying to describe a mechanism for reactionless thrust, which would violate physics.

Quote from: Halc
As for using a bigger wheel at one end and constant belt speed, that indeed makes no changes except that the weight isn't going to slow at one end or the other.  There will be no acceleration/deceleration since you specified constant belt speed.
I wanted to say that centrifugal force will be bigger on a top of conveyor and less at the bottom of it. After sum of two forces you have force in direction against gravity.
The mass spends twice the time at the bottom going around the circumference of the larger wheel, so half the force for double the time makes for zero net difference.

The forces that are depicted in the picture point the wrong way.  The weight is going to pull on the belt, not the wheels.  Tension on the belt is what pulls the opposite wheel, so the weight going over the top will put tension on the belt that pulls up on the lower wheel.  The weight going slow at the bottom pulls down at a minimum on the upper wheel.  Same net effect, but the wheels are always being pulled together in such a setup and would need some sort of bar to keep them separated.

What is missing from the picture is the reaction thrust needed to accelerate the weight as it goes up and down.  That (in both directions) causes a downward force on the upper wheel that exactly cancels the upward force on the lower wheel.
Title: Re: What is centrifugal force?
Post by: Vasyl on 19/11/2018 20:16:38
I think you're trying to describe a mechanism for reactionless thrust, which would violate physics.
I have understood my mistake. I knew that reactionless thruster is fake but I didn't see it in mechanism above. No, I am not trying to violate physics' laws. Now, I see my mistake, thanks.
Title: Re: What is centrifugal force?
Post by: Vasyl on 22/11/2018 17:08:20
What is missing from the picture is the reaction thrust needed to accelerate the weight as it goes up and down.  That (in both directions) causes a downward force on the upper wheel that exactly cancels the upward force on the lower wheel.
By the way, Newton's third law is fulfilled. On the picture you see two conveyors which are rotated in different directions like in helicopter with two propellers.
Title: Re: What is centrifugal force?
Post by: rmolnav on 16/12/2018 11:56:40
The formula for centrifugal force (in a rotating frame) is mωr (where ω is angular velocity, labeled as L in the picture).  mv2/r is centripetal force, but in a rotating frame, v is zero, so that doesn't work.  In an inertial frame, there is no centrifugal force.
I don´t know if you have gone on reading the really long discussion David Cooper and myself have had on the thread "Why we do have two high tides a day?" ...
Most important question there have been precisely whether what discussed here, centrifugal force, intervenes or not in the formation of tides ...
Over last several months I´ve got a rather fresh approach to the issue, especially to its relation to the idea, as in what quoted from you, that " In an inertial frame, there is no centrifugal force".
What follows is my post #382 in mentioned thread, and it might be interesting for you, or other members, at least to have a look at.
"MY ULTIMATE GO ? (5th part)
Before trying and conveying my stand on non-inertial frames issue, let us go back to the drawing board, as if we didn´t have any education on dynamics …
Same image with Earth (E) on upper part, and vertically below the Moon (M).
Let us suppose we only know how they move, with kind of the mind of a “smart” child.
And then we learn that (as David Cooper said many times), if Earth and Moon tangential speeds somehow became null, they would begin to accelerate straightly towards each other, because of gravitational mutual attraction …
If just stopping their circular movements, they get “free” to accelerate towards each other … THOSE CIRCULAR MOVEMENTS ARE WHAT, WHEN EXISTING, WERE SOMEHOW COUNTERING THOSE STRAIGHT ACCELERATIONS NOW THEY HAVE GOT !!  No other logical possibility for a “clean” child mind …
How come? Let us see …
Curiously, with a rotating (so called "non-inertial”) frame of reference, same thing happens, but let us say “virtually” …
As the frame of reference rotates with E and M, E and M don´t "rotate" anymore  relatively to that frame of reference … Centripetal forces are not required whatsoever, and gravitational pull would make them fall onto each other … But that´s far from reality …
Then physicists go on: "How can we do “real” maths with that “artificial” (the adjective is mine ...) reference system ? … We have to apply a “fictitious” force, which we´ll call centrifugal force". That way WE GET BACK TO THE REAL SCENARIO … as far as dynamics is concerned.
Well, that force is certainly “fictitious”, because it has been introduced by us to work with that non-inertial frame of reference … BUT THAT MEANS THAT THE REAL CIRCULAR MOVEMENTS, NOT NEEDING THE ADDITION OF ANY “ARTIFICIAL” FORCE, SOMEHOW PRODUCE AN INERTIAL EFFECT THAT KEEPS E AND M WITHOUT FALLING STRAIGHTLY ONTO EACH OTHER !! TO ME (AND NOT ONLY ME), THAT IS A CENTRIFUGAL FORCE, QUITE REAL !!
In case B (1st part of “MY ULTIMATE GO ?"), as E and M were moving horizontally at same speed, Moon´s pull was able not only to bend E´s trajectory, but also to accelerate E straightly towards M with its full strength, quite a “free” acceleration. That “freedom” was made possible by the movement of the moon towards the left, with same horizontal speed as E.
The real case is dynamically quite the opposite: the movement of M in opposition to E´s speed, and with speeds which make them to revolve/rotate around the barycenter, makes impossible the decrease of E-M distance, and even any proper orbiting of E around M. It gives us a “rotating” scenario, where all forces have basically same direction as the line between centers of mass, and where the angular position doesn´t matter much (as far as Earth-Moon dynamics is concerned), as long as we accept centrifugal forces keep the separation constant …
After all, if Earth and Moon were the only celestial objects in the universe, to talk about angular position of the system would have no sense at all …
BUT, STILL, THE WOULD HAVE TO KEEP ROTATING. THAT WAY INHERENT INERTIAL FORCE, THE CENTRIFUGAL FORCE, WOULD KEEP THEM WITHOUT FOLLOWING STRAIGHTLY ONTO EACH OTHER !! 
Therefore, as I´ve said many times, I find quite correct what a NOAA scientist told me:
"... to provide a basic description of the forces which create the tides.  It's intended audience were the grade school children and adults of that time.  It used terminology of science and forces which were common in the 1950s.  Such as centrifugal force.  Centrifugal force was always an "imaginary force" (not a real / measurable force).  But that type of description made the concepts easier to understand and explain.  That  description and use of centrifugal force continued to be common practice until the 1970-80's.  At that point, the terminology shifted and the TEXTBOOKS USED IN GRADE SCHOOLS WERE CHANGED TO USE A MORE MODERN TERMINOLOGY AND DESCRIPTION OF THIS “EFFECT”BEING A RESULT OF INERTIA RATHER THAN AN “IMAGINARY FORCE”".
Initially I didn´t fully grasp his point ... But later I did.
The problem is that many books, dictionaries included, keep following models with ideas which are several decades out of date …"


   

 
Title: Re: What is centrifugal force?
Post by: PmbPhy on 16/12/2018 20:43:52
What is centrifugal force?
Its the force on an object resulting from observing the object in a rotating frame of reference.

In the previous discussion Alancalverd stated that there was no such thing as centrifugal force.
That's because he uses a definition of force which applies only in inertial frames.

I recommend reading the web page I created on this subject at:
http://www.newenglandphysics.org/physics_world/gr/inertial_force.htm
Title: Re: What is centrifugal force?
Post by: Halc on 16/12/2018 23:56:43
Same image with Earth (E) on upper part, and vertically below the Moon (M).
Let us suppose we only know how they move, with kind of the mind of a “smart” child.
And then we learn that (as David Cooper said many times), if Earth and Moon tangential speeds somehow became null, they would begin to accelerate straightly towards each other, because of gravitational mutual attraction …
They would not 'begin' to accelerate towards each other.  They're already accelerating towards each other.  Gravity is the force, and a=F/m, so the acceleration of each can be computed.  Stopping their tangential motion changes that force and associated acceleration not one hoot.  Of course if their separation starts to shorten, that force will increase accordingly.

Quote
Curiously, with a rotating (so called "non-inertial”) frame of reference, same thing happens, but let us say “virtually” …
If we're in a rotating frame, the moon is already stationary, so there is no taking away its tangential speed.  It hasn't any.  In that scenario, gravity is countered exactly by centrifugal force, and hence the net force is zero, and the moon remains stationary.  All very nice and stable.

Quote
As the frame of reference rotates with E and M, E and M don´t "rotate" anymore  relatively to that frame of reference … Centripetal forces are not required whatsoever, and gravitational pull would make them fall onto each other … But that´s far from reality …
For some reason you omit centrifugal force in this example, but you seem to get it.

Quote
Then physicists go on: "How can we do “real” maths with that “artificial” (the adjective is mine ...) reference system ?
There's nothing artificial about different reference systems.  They all are legit, but each have different rules.  Things move faster than light in rotating frames.  Not a problem.  Time moves backwards in portions of  accelerating frames.  Again, not a problem since those portions sort of don't exist in those frames.
Title: Re: What is centrifugal force?
Post by: alancalverd on 17/12/2018 09:32:02
In the previous discussion Alancalverd stated that there was no such thing as centrifugal force.

I sincerely hope I didn't! Others, and the writers of trendy textbooks, deny its existence, but I have felt the tug on the string, and wondered why, if the only force on a rotating object is centripetal, the tyres fly off wheels at high speed and the denser parts of blood end up on the outside of the centripete (just because it says "centrifuge" on the outside of the machine doesn't mean that generations of scientists, engineers and aviators knew what they were talking about, children!)

"Ah, but if you cut the string, the stone doesn't fly away from the center!" Oh yes it bloody does. Tangentially, not radially, but still away from the center (assuming that you and I share the definition of "away").

Here's the simple truth

1. A body continues in a straight line unless acted upon by a force.

2. To make a body turn in a circle, you need to apply a force towards the center of the circle

3. Every action provokes an equal and opposite reaction

so the tension pulling the stone inwards is balanced by the force I feel pulling my hand outwards

But ...... and here's a paradox for those interested in such things..... if the inward and outward forces are identical, there is no net force inward, so the stone doesn't move in a circle after all! The inward force must exceed the outward force! Free energy, perpetual motion, collapse of Newtonian physics......
Title: Re: What is centrifugal force?
Post by: PmbPhy on 18/12/2018 00:55:08
...... and here's a paradox for those interested in such things..... if the inward and outward forces are identical, there is no net force inward, so the stone doesn't move in a circle after all!
/quote]
That is an invalid deduction. Zero radial force means zero radial acceleration. From an inertial frame, if an object is moving in a circle then the outward force is balanced by the centripetal force. That doesn't mean that all other forces are zero. Acceleration is a vector quantity and the acceleration vector is non-zero since the object is not moving in a straight line.

Buy the way. I forgot to mention that in a rotating frame the Coriolis force is non-zero and is a velocity dependent force. Centripetal force is the radially inward force acting on body to make it move in a circle.
Title: Re: What is centrifugal force?
Post by: alancalverd on 18/12/2018 09:13:05
I wish there was a "tongue in cheek" emoticon, but Nemesis Pete is just as effective!
Title: Re: What is centrifugal force?
Post by: rmolnav on 18/12/2018 11:49:10
"Ah, but if you cut the string, the stone doesn't fly away from the center!" Oh yes it bloody does. Tangentially, not radially, but still away from the center (assuming that you and I share the definition of "away").
I´ve long been defending the existence of real centrifugal forces ("real" meaning they produce physical effects), and many times have seen stuff similar to what quoted  ...
But I´m afraid your approach isn´t fully correct.
Whatever definition we give to "away", that tangential movement has NOTHING TO DO with any centrifugal force, because, since the very moment you cut the string, both centripetal and centrifugal force DOESN´T EXIST any more ... Therefore, the stone keeps the velocity vector it has at that moment ! (Newton´s First Motion Law).
 
3. Every action provokes an equal and opposite reaction, so the tension pulling the stone inwards is balanced by the force I feel pulling my hand outwards
Newton´s Third Motion Law doesn´t actually say " Every action provokes an equal and opposite reaction" ... Though First and Second Laws refer to a single object, Third Law refers to TWO objects, and mentioned "action" and "reaction" forces are exerted by each of them ON THE OTHER !!
And your phrase " ...the tension pulling the stone inwards is balanced by the force I feel pulling my hand outwards" deals with THREE objects: stone, string and your hand ...
You have to analyse each directly interacting pair separately.
1) Outer string end has to exert an inward force (centripetal), to "bend" stone trajectory ... Due to inertia phenomenon, the stone exerts an outward force (centrifugal, in its ample sense) ON THE STRING END ... "Net force inward" doesn´t become null whatsoever: to add force vectors applied on different objects has no sense at all !!
2) To produce above mentioned centripetal force on the stone, the string has to be tight ... YOU have to pull inwards the inner end of the string: centripetal force exerted on that end OF THE STRING ... As a reaction the string exerts an outward force ON YOUR HAND (the one you certainly feel).
And those two pair action/reaction forces, though being each pair equal but opposite, have different sizes. Apart from friction energy wasted, the string is also rotating and requires a "net" inward force exerted on it: your pull on inner end the string has to be bigger than the outward pull of the stone on outer end of the string ...
QUITE ANOTHER thing is the question of inertial "effects" on the accelerated object ITSELF ... The stone internally "feels" is being accelerated, and internal stresses do appear ... If the stone is connected to the string through a hook on its surface, those internal stresses are tensile. But in the case of a sling, they are compressive, quite the opposite.
Even more "tricky" is the case when, instead of a "physical" connection such as a string, it is the gravitational pull of another massive object what exerts as centripetal force and "forces" the first object to bend its trajectory ...
That´s what I´ve long been discussing on "Why do we have two high tides a day", as I said here a couple of days ago ...
It is very interesting what linked by PmbPhy,  http://www.newenglandphysics.org/physics_world/gr/inertial_force.htm
As I´ve said several times I think inertia, and frames of reference "tool", are rather misunderstood/misused by many. But I need further "rumination" on the lot of things said on that link, before any other comment.
Title: Re: What is centrifugal force?
Post by: alancalverd on 18/12/2018 13:52:44
Whatever definition we give to "away", that tangential movement has NOTHING TO DO with any centrifugal force, because, since the very moment you cut the string, both centripetal and centrifugal force DOESN´T EXIST any more ... Therefore, the stone keeps the velocity vector it has at that moment ! (Newton´s First Motion Law).

If it moves away when I cut the string, the string must have been exerting some force on it before the cut.
Title: Re: What is centrifugal force?
Post by: rmolnav on 18/12/2018 18:23:28
Whatever definition we give to "away", that tangential movement has NOTHING TO DO with any centrifugal force, because, since the very moment you cut the string, both centripetal and centrifugal force DOESN´T EXIST any more ... Therefore, the stone keeps the velocity vector it has at that moment ! (Newton´s First Motion Law).
If it moves away when I cut the string, the string must have been exerting some force on it before the cut.
Come on ! That´s obvious ...
But, on the one hand, what you had previously said is that movement "away" should be due to a "centrifugal" force ... Now you say "the string must have been exerting some force on it before the cut" ... But the existence of that force, which is "centripetal", doesn´t prove the existence of any centrifugal force moving "away" the stone ...
On the other hand, what that force (certainly existing before the cut) actually does is ONLY to make the stone get the velocity vector it has at the moment when the string is cut ... Neither a centripetal force, nor (and "let alone") a centrifugal one is acting on the stone after the cut ... As people now say "we are now on another screen" ... And the stone just continues straight and at constant speed, the way inertia manifests itself when no force is exerted on massive moving objects (not considering stone weight and air friction, what initially have only small curving effects).
Title: Re: What is centrifugal force?
Post by: David Cooper on 18/12/2018 23:54:17
I've only just found this thread - I rarely find enough time to explore the forum beyond looking up new replies to threads I've posted in.

But ...... and here's a paradox for those interested in such things..... if the inward and outward forces are identical, there is no net force inward, so the stone doesn't move in a circle after all! The inward force must exceed the outward force! Free energy, perpetual motion, collapse of Newtonian physics......

This relates to something that's been bothering me.

If you have a ball on a string going round some relatively fixed point to which it's tied, centripetal force is generated in the string in one direction while "reactive centrifugal force" (the only real kind of centrifugal force) is generated the opposite way in the string.

If we have two objects of equal mass on opposite ends of a string which are going round each other, the string then has both centripetal and reactive centrifugal forces running through it in both directions in equal amounts.

If the forces in opposite directions through the string are equal though (and we can see very clearly in this example that they should be), how do the objects follow circular paths instead of moving along straight lines? In the case of the single ball case where the other end of the string's attached to a fixed point, you can imagine that the forces are equal when analysed in a rotating frame, but not equal when analysed from a non-rotating frame, but that doesn't look possible in the case with the two balls of equal mass both going round in circles on the same path - in the analysis from a rotating frame, the forces each way through either end of the string can be considered to be equal, but it looks as if the same must apply when you analyse it from a non-rotating frame.

Is it somehow possible for the forces only to be equal in the middle of the string but not equal towards the ends so that the balls don't follow straight lines?
Title: Re: What is centrifugal force?
Post by: Halc on 19/12/2018 00:19:09
Is it somehow possible for the forces only to be equal in the middle of the string but not equal towards the ends so that the balls don't follow straight lines?
Depends on the mass ratio of the ball going around and the of the object to which we've tied the string.  So if the 'anchor' is 99x the mass of the ball, the point 1% down the string is balanced in the sense that the string there has no acceleration.

The forces are equal along the entire length of the string, assuming an ideal massless string, which doesn't correspond to reality.  In reality, the tension on the string is largest at the 'axis' since the mass of the string adds to the mass of the ball.
Title: Re: What is centrifugal force?
Post by: rmolnav on 19/12/2018 12:59:38
Is it somehow possible for the forces only to be equal in the middle of the string but not equal towards the ends so that the balls don't follow straight lines?
Leaving aside the questions of the generation of the rotating "scenario" and what relative to frames of reference (long discussed on the other thread), I think you´re making an error similar to what I told "alancalverd" « on: Yesterday at 11:49:10 »
The balls would follow straight lines if two equal but opposite forces were being exerted on each of them ... But what actually happens at both string connections to the balls is that string exerts the centripetal force ON THE BALL, and each ball exerts the centrifugal force ON THE STRING END ... (Third Newton´s Motion Law).
Therefore, on each ball only a centripetal force is applied ...
But, as I said yesterday:
QUITE ANOTHER thing is the question of inertial "effects" on the accelerated object ITSELF ... The stone internally "feels" is being accelerated, and internal stresses do appear ... If the stone is connected to the string through a hook on its surface, those internal stresses are tensile. But in the case of a sling, they are compressive, quite the opposite.
.
And if e.g. the balls were wet, with water on their surface, that water would "feel" a centrifugal force that, despite surface tension, would make the water move towards outer sides of the balls ...
All that occurs in a way very similar to what happens on earth, due to its revolving around moon-earth barycenter. Though in earth case water also  "feels" other forces: pretty constant own weight, and variable moon´s gravitational pull, and ALL mentioned forces cause moon-related tides ...
By the way, ALL THAT has nothing to do with reference systems: it can be seen whatever the observer is rotating with the balls, with the earth, with the moon ... or from an independent spaceship !!
Title: Re: What is centrifugal force?
Post by: David Cooper on 19/12/2018 22:21:08
The balls would follow straight lines if two equal but opposite forces were being exerted on each of them ... But what actually happens at both string connections to the balls is that string exerts the centripetal force ON THE BALL, and each ball exerts the centrifugal force ON THE STRING END ... (Third Newton´s Motion Law).
Therefore, on each ball only a centripetal force is applied ...

That's what I was missing. Thanks. So the two forces are absolutely equal at any point along the string (but both slightly higher towards the centre). It's in the rotating frame then that the centrifugal force is calculated as acting on the ball to push it outwards as much as it's being pulled in, but that's a radically different approach - I was mistranslating between the two.
Title: Re: What is centrifugal force?
Post by: alancalverd on 19/12/2018 23:27:07
So if I spin a blood sample in a "centrifuge", what makes the denser elements move outwards? It can't be the effect of a centripetal force pulling the lighter liquid inwards, because you can't pull a liquid.
Title: Re: What is centrifugal force?
Post by: rmolnav on 20/12/2018 08:01:17
So if I spin a blood sample in a "centrifuge", what makes the denser elements move outwards? It can't be the effect of a centripetal force pulling the lighter liquid inwards, because you can't pull a liquid.
That case is kind of similar to the sling case, where due to the fact that the stone is PUSHED inwards by the string loop (centripetal force), the stone also PUSHES the string loop outwards (centrifugal force), and the stone is "compressed" internally.
The centrifuge container "forces" outer blood layer to turn (thanks to friction), and that is transmitted inwards layer to layer ... Between two contiguous layers Third Newton´s Motion Law also applies, and inner layer PUSHES outer one outwards (centrifugal force), what increases pressure, the outer the more ... ALL blood elements tend to go outwards, but denser ones "win" the battle, and they move outwards, not letting lighter ones do the same ... (similarly to the static case where denser elements go down, and lighter ones up).
Initially it´s the same reason why in a cylindrical container filled with a not homogeneous liquid, if spinning round its vertical axis, liquid surface gets an inverted paraboloid shape: liquid  pressure horizontally increases, the outer the more, and denser elements "concentrate" at outer bottom zones ... But the centrifuge is suitably perforated, and denser elements go out first and get separated from lighter ones.
Title: Re: What is centrifugal force?
Post by: rmolnav on 21/12/2018 08:43:32
Initially it´s the same reason why in a cylindrical container filled with a not homogeneous liquid, if spinning round its vertical axis, liquid surface gets an inverted paraboloid shape
In the case of a non homogeneous liquid such as blood, surface shape is similar to a paraboloid, but not exactly equal, as can be seen below.
To add some maths to what quoited, you can have a look at what some time ago I sent to another s science-related blog:
"Let us imagine the cylinder of water inside the spinning bucket broken up into a number of telescopic pipe-shaped volumes of water.
Certainly water at the bigger of those volumes, in contact with the bucket, just tries to keep constant its speed vector, value and direction (Newton´s 1st law).
But the bucket makes it impossible, exerting an inward pressure that causes centripetal forces for the rotation.
And due to Newton´s 3rd law, the water exerts an outward, centrifugal reaction force.
Something similar to that can be said about the interaction between that bigger, most outer pipe-shaped volume, and the inner contiguous one ... and so on up to the axis of rotation.
On each “pipe” two opposite forces (pushes) are exerted: one by outer contiguous pipe (centripetal), an another by the inner contiguos pipe (centrifugal). First one has to be bigger than second one, in order to have a net centripetal force to make that water rotate.
On the one hand, centripetal acceleration has to be equal to the angular speed to the square, multiplied by the radius (ω˛r). Then, it is proportional to the radius.
On the other hand, as f=ma (Newton´s 2nd law), the force “f” has to be also proportional to mass “m”.
But “m” is proportional to volumes (watch out: ONLY if uniforme density, as with water: NOT in the blood case). Let us consider 1 cm high horizontal slice of that "telescopic device”. Volumes are proportional to the square of the radius.
So, centripetal force is proportional to the radius to the cube (exponent 3 equal to 1+2, proportionality due to acceleration + prop. due to mass).
But in Fluid Mechanics pressure is paramount value, force divided by surface.
As vertical surfaces of those 1 cm telescopic slice water “rings” are proportional to their radius, “centripetal” pressure has to be proportional to the square of the radius (exponent 3 due to proportionality related to force minus 1, due to proportionality related to surface).
But in liquids that pressure, in a given point, is the same whatever the orientation of the considered surface. When in a dynamic equilibrium, the weight of a vertical water column of 1 cm2 section, from a given point to water upper surface, has to be also proportional to the square of the radius.
So, that column of water has to have a hight proportional to the square of the radius ... : the shape of a paraboloid !"
And that physical phenomenon offers different possibilities to practically separate  denser particles in a centrifuge from lighter ones ...
Title: Re: What is centrifugal force?
Post by: rmolnav on 22/12/2018 11:31:33
I´m going to size the opportunity that the "centrifuge" case, as explained on my last posts, gives us ... What for? To explain why many times I´ve said the question of inertial and not inertial frame of references are erroneously used by many (at least in a misleading way). E.g.:
Quote from: jerrygg38 on 14/08/2016 19:21:31
What is centrifugal force?
It´s the force on an object resulting from observing the object in a rotating frame of reference.
Quote from: jerrygg38 on 14/08/2016 19:21:31
In the previous discussion Alancalverd stated that there was no such thing as centrifugal force.
That's because he uses a definition of force which applies only in inertial frames.
you can imagine that the forces are equal when analysed in a rotating frame, but not equal when analysed from a non-rotating frame
Even knowledgable people consider we have always to add the phrase "relative to a non-inertial frame of reference", if we mention "centrifugal force". And they even add the adjective "fictitious", and think no centrifugal force is real ...
In the case of the centrifuge, and in many others, we can see REAL inertial effects such as the increase of pressure proportionally to the square of the distance from the axis of spinning ... WHATEVER the frame of reference ...
And that increase of pressure only can be due to the existence of both centripetal and centrifugal forces, the former due to the fact that some energy source is making the bucket rotate, and the later REAL inertial forces (as explained on my last posts).
Let us imagine  a huge cylindrical bucket, with a vertical shaft along its axis, and with a seat  on top.
If it is partially filled with water and made spin, for an observer on the seat, after some transient situation (friction needs time to make all water spin ...)  APPARENTLY there would be no rotation, because it´s the case of a so called "non-inertial" reference system ...
If "no" rotation, no centripetal acceleration is required, and no manifestation of inertia such as centrifugal force could "exist" ...
But still, he is seeing water surface changes from flat into a paraboloid !!
In that "artificial" scenario, he can´t explain what happens ...
"It´s easy", physicists say ... If you apply "fictitious!" outward forces (equal to ω˛r per unit of mass, being ω the angular speed of rotation of the "observer"), you have a "sound" scenario (the adjective is mine) and you can make any calculation using that "non-inertial" frame of reference !!
I do understand there are cases where those rotating frames of reference can be useful for calculations, but to say centrifugal force ONLY can be that "fictitious" one, and always related to the chosen system of reference, is utterly erroneous ...
At least in the analyzed case, Logics leads me to say quite the opposite: "suppressing" the rotation (relatively to the "rotating" frame of reference), requires the application of "fictitious" centrifugal forces ... precisely the REAL ones which "previously" existed, and have disappeared relatively to the non-inertial frame of reference !!
Title: Re: What is centrifugal force?
Post by: David Cooper on 22/12/2018 19:35:40
You quoted me saying "you can imagine that the forces are equal when analysed in a rotating frame, but not equal when analysed from a non-rotating frame" in your last post, and I want to comment on that. It refers to the case of a ball on the end of a string going round in circles, the other end of the string fixed to something that doesn't move.

With the rotating frame, there's an imaginary centrifugal force pulling the ball one way and centrifugal force pulling it the other way, and these two forces are equal, so the ball stays the same distance from the centre.

With the non-rotating frame, there's no centrifugal force pulling the ball in the opposite direction from the centripetal force. What we do have though is reactive centrifugal force opposing the centripetal force in the string, and they are again equal in strength.

Going back to the rotating frame, the centripetal force in the string must also be opposed by an equal and opposite force, and this job is presumably imagined to be done by the imaginary centrifugal force instead of by reactive centrifugal force, so the centrifugal does the same job as reactive centrifugal force while also trying to accelerate the ball away from the centre.

In reality, rotating frames are an abstraction, and the result of using that abstraction is that imaginary forces come into play that don't exist in reality (or where part of their role is real but the other part is fake). All the things in nature that are imagined to be centrifugal force must actually be the real force called reactive centrifugal force which merely opposes centrifugal force. If we have a mouse clinging to a hamster wheel and spinning round inside it very fast (after it stops running suddenly), the rim applies centripetal force inwards against the mouse (applying pressure to it), and the reactive centrifugal force is where the mouse presses back against the rim of the wheel. With the ball on the string, the centripetal force is applied as a tension from the other side, and the reactive centrifugal force is also applied as a tension in the opposite direction. In a centrifuge, we have a case like the mouse in the wheel rather than a ball on a string, but we're still dealing with the real force called reactive centrifugal force, and that force only ever exists as a reaction opposing centripetal force. No one should be rejecting the existence of reactive centrifugal force, and no one should be asserting the existence of centrifugal force of the other kind because it is only an artefact of an abstraction - it is the latter kind that has been rejected by science, and the two should not be mistaken for each other.
Title: Re: What is centrifugal force?
Post by: Vasyl on 23/12/2018 08:13:41
No one should be rejecting the existence of reactive centrifugal force, and no one should be asserting the existence of centrifugal force of the other kind because it is only an artefact of an abstraction - it is the latter kind that has been rejected by science, and the two should not be mistaken for each other.
The more I read, the less I understand. Could you please help me to understand one thing: Is it possible to accelerate a particle (like in Hadron Collider) in a closed system, for example in a deep space?
Title: Re: What is centrifugal force?
Post by: rmolnav on 23/12/2018 12:13:08
No one should be rejecting the existence of reactive centrifugal force, and no one should be asserting the existence of centrifugal force of the other kind (??) because it is only an artefact of an abstraction - it is the latter kind that has been rejected by science, and the two should not be mistaken for each other.
I´m not going to continue to discuss with you some "details" we have long discussed on the "tides" thread, to no avail ...
But please kindly note that you can find definitions of "centrifugal force" considering it ONLY as a "fictitious" force ...
E.g.,  on "Britannica.com", certainly with physicists as technical advisers, the definition is just:
"Centrifugal force, a fictitious force, peculiar to a particle moving on a circular path, that has the same magnitude and dimensions as the force that keeps the particle on its circular path (the centripetal force) but points in the opposite direction".
Though, curiously, further down they themselves give links to other britannica articles, among others precisely the "centrifuge" one where you can read:
"Centrifuge, any device that applies a sustained centrifugal force—that is, a force due to rotation. Effectively, the centrifuge substitutes a similar, stronger, force for that of gravity. Every centrifuge contains a spinning vessel; there are many configurations, depending on use. A perforated rotating drum in a laundry that throws off excess water from clothes, for example, is a type of centrifuge. A similar type is used in industry to separate fluids from solid matter after crushing",
and, logically, that "centrifugal force" has to be REAL ... They just say "due to rotation", without any reference either to centripetal force (the one exerted by the spinning vessel on the liquid to make it follow a circular path), or to the inertial outwards reactive forces exerted by the liquid, both internally between cylindrical layers of liquid, and on the inner side of the vessel ...
And those forces are "centrifugal" and real: otherwise pressure would not increase outwards, as explained on my last posts !!
By the way, what happens in the centrifuge case in some aspect is similar to what in the case of a ball being made rotate with a sling, "pushing" it inwards (on its outer side), instead of "pulling" from a hook on its inner side (as when hammer throwing) ... The sling rotation (together with inertia) produces compressive forces inside the ball, the outer the more, as in the centrifuge the vessel spinning and inertia cause the increase of pressure, the outer the more too !!

Title: Re: What is centrifugal force?
Post by: David Cooper on 23/12/2018 19:36:54
No one should be rejecting the existence of reactive centrifugal force, and no one should be asserting the existence of centrifugal force of the other kind because it is only an artefact of an abstraction - it is the latter kind that has been rejected by science, and the two should not be mistaken for each other.
The more I read, the less I understand. Could you please help me to understand one thing: Is it possible to accelerate a particle (like in Hadron Collider) in a closed system, for example in a deep space?

Why wouldn't that be possible, and why are you relating that to centrifugal force?
Title: Re: What is centrifugal force?
Post by: Vasyl on 23/12/2018 19:57:04
Why wouldn't that be possible, and why are you relating that to centrifugal force?
If it is possible than we can create artificial "asteroids" and attach a spaceship to them to explore space. Or is it not possible?
Title: Re: What is centrifugal force?
Post by: David Cooper on 23/12/2018 19:59:54
No one should be rejecting the existence of reactive centrifugal force, and no one should be asserting the existence of centrifugal force of the other kind (??) because it is only an artefact of an abstraction - it is the latter kind that has been rejected by science, and the two should not be mistaken for each other.
I´m not going to continue to discuss with you some "details" we have long discussed on the "tides" thread, to no avail ...

The problem there was that you wanted to have some kind of centrifugal force involved in cases where the centripetal force is gravity, but there is absolutely no centrifugal force of any kind involved in that other than in the abstraction of rotating-frame analysis.

Quote
But please kindly note that you can find definitions of "centrifugal force" considering it ONLY as a "fictitious" force ...

Inadequate definitions exist all over the place, but we don't need to trip over them. The whole point of working to acquire a deep understanding of the physics in places like this forum is to become better able to tell whether what you're reading is correct or faulty. Often the faults are in omission where someone has written something with only one thing in mind and hasn't thought to clear up other issues, in this case because of an ambiguity. Different contributors to an encyclopaedia can use ambiguous words in different ways, all intending to provide good information (and doing so if you read them the right way), but the different ways in which they word things can appear to produce contradictions.

Quote
Though, curiously, further down they themselves give links to other britannica articles, among others precisely the "centrifuge" one where you can read:
"Centrifuge, any device that applies a sustained centrifugal force—that is, a force due to rotation.

You're first Britannica quote dismisses centrifugal force entirely (because the writer is only thinking about the fictitious kind of centrifugal force of the kind that provides the illusion of existing in rotating frames), but your second one which refers to a sustained centrifugal force is actually talking about reactive centrifugal force which is a real force - it is just referred to in a more economical way (by missing out the word "reactive") that depends on the reader applying correct understanding to it. That way of wording things is the standard way of doing so when talking about a centrifuge. It is your job to catalogue the information correctly in your head, filing it under "reactive centrifugal force" rather than "centrifugal force".

Quote
and, logically, that "centrifugal force" has to be REAL ... They just say "due to rotation", without any reference either to centripetal force (the one exerted by the spinning vessel on the liquid to make it follow a circular path), or to the inertial outwards reactive forces exerted by the liquid, both internally between cylindrical layers of liquid, and on the inner side of the vessel ...

Your understanding of physics should enable you to link the thing they're calling "centrifugal force" to the correct real phenomenon and not to be misled into thinking there is some other centrifugal force involved in the situation.

Quote
And those forces are "centrifugal" and real: otherwise pressure would not increase outwards, as explained on my last posts !!

The centripetal force is higher further out, and the reactive centrifugal force goes up to match that - the thing being called centrifugal force in a centrifuge is the reactive force responding to the centripetal force.

Quote
By the way, what happens in the centrifuge case in some aspect is similar to what in the case of a ball being made rotate with a sling, "pushing" it inwards (on its outer side), instead of "pulling" from a hook on its inner side (as when hammer throwing) ... The sling rotation (together with inertia) produces compressive forces inside the ball, the outer the more, as in the centrifuge the vessel spinning and inertia cause the increase of pressure, the outer the more too !!

And I suppose you think I didn't say that in the post you're attacking. Note where I talk about tension and pressure in relation to how the centripetal force is applied. Ball on string --> tension; mouse in hamster wheel --> pressure.
Title: Re: What is centrifugal force?
Post by: David Cooper on 23/12/2018 20:04:27
Why wouldn't that be possible, and why are you relating that to centrifugal force?
If it is possible than we can create artificial "asteroids" and attach a spaceship to them to explore space. Or is it not possible?

Are you sure you're posting in the right thread? Why would you want to handicap a space probe by tying an artificial or real asteroid to it? The less mass (other than fuel) that you have to accelerate, the easier it is for the probe to go exploring, and the higher the speed you'll get it to.
Title: Re: What is centrifugal force?
Post by: rmolnav on 28/12/2018 08:40:53
your second one which refers to a sustained centrifugal force is actually talking about reactive centrifugal force which is a real force - it is just referred to in a more economical way (by missing out the word "reactive") that depends on the reader applying correct understanding to it.
As I´ve already said, it´d be useless to continue here our so long discussion
on the thread about tides ...
But I want to repeat I don´t agree with some of your "basic" dynamics ideas, e.g., what quoted ...
Centrifugal forces, the ones really acting in nature, are always manifestations of inertia when physical objects are accelerated "centripetally" (therefore, moving along a curved trajectory), whatever the essence of the required centripetal force and rest of circumstances.
The "fictitious" ones only "exist" inside our minds, when we use rotating frames of reference for our calculations ... In that "virtual" scenario, as actually rotating objects kind of "stop" their rotation (--> no centripetal acceleration and no inertial effects), we "need" to introduce a "fictitious" external centrifugal force, that causes effects IDENTICAL to the ones actually caused by the sheer fact of the kind of "hidden" rotation ...   
But those effects do exist in the real, natural scenario.
By the way, this very morning I saw a clip on Discovery Max tv, where a CD was made rotate at the r.p.m. of a hoover ... The CD suddenly breaks into hundred of small pieces, obviously due to huge tensile internal stresses due to both centripetal and centrifugal forces (the former causing the rotation, and the later the way inertia manifests itself, because all CD particles are being hugely accelerated).
And that, happening in nature, has nothing to do with frames of reference !!
 
Title: Re: What is centrifugal force?
Post by: rmolnav on 31/12/2018 08:45:23
By the way, this very morning I saw a clip on Discovery Max tv, where a CD was made rotate at the r.p.m. of a hoover ... The CD suddenly breaks into hundred of small pieces, obviously due to huge tensile internal stresses due to both centripetal and centrifugal forces (the former causing the rotation, and the later the way inertia manifests itself, because all CD particles are being hugely accelerated).
And that, happening in nature, has nothing to do with frames of reference !!
 
Before the year ends ... Happy New Year! ...
...and an additional comment to what above.
In the case of the CD, as in the cases of the centrifuge, the hammer throwing, the sling ..., "solid" stuff is what exerts the centripetal force on the considered rotating "object" (either solid or liquid), and centrifugal forces (inertial as always) are exerted by the rotating "objects" on what exerts the centripetal force (internal stresses included).
Some people think that when gravity is involved (as cause of the curving of the trajectory), without any solid device (such as a string, wire, centrifuge vessel, and own CD material), no centrifugal force exists ...
But quite similar to the CD case is the daily earth spinning ... At its angular speed of 2π radians/24 h. it is causing a relatively huge equatorial bulge (tens of km), affecting both solid and liquid parts of our planet.
Earth solid parts are stretched as in the CD case, and also would explode at much higher velocity.
But what makes water rotate (instead of "following the tangent) is only gravity, exactly a component of water weight vector at each location: the one perpendicular to earth´s axis of rotation ...
At the equator water "lightens" much more than closer to poles, because centrifugal forces are proportional to the radius (mω˛r) ...
If spinning velocity increased, the bulge would get bigger, water would evaporate more ... and eventually something similar to the case of the CD at vacuum cleaner spinning rate would happen !!
Centripetal and real centrifugal forces are necessary for all that to happen, and, again, whatever the movement of any considered observer, and the reference system he or she chose...
Title: Re: What is centrifugal force?
Post by: David Cooper on 31/12/2018 23:04:14
Before the year ends ... Happy New Year! ...

Happy Calendar-Replacement Day!

Quote
In the case of the CD, as in the cases of the centrifuge, the hammer throwing, the sling ..., "solid" stuff is what exerts the centripetal force on the considered rotating "object" (either solid or liquid), and centrifugal forces (inertial as always) are exerted by the rotating "objects" on what exerts the centripetal force (internal stresses included).

... which is known as reactive centrifugal force (the only kind of centrifugal force that actually exists).

Quote
Some people think that when gravity is involved (as cause of the curving of the trajectory), without any solid device (such as a string, wire, centrifuge vessel, and own CD material), no centrifugal force exists ...

... and those people are certainly right in cases where there is no contact between them.

Quote
Centripetal and real centrifugal forces are necessary for all that to happen, and, again, whatever the movement of any considered observer, and the reference system he or she chose...

An object sitting on a non-rotating planet will press down on the surface of the planet and a reactive force will be generated in the opposite direction to oppose it. Neither of those forces can be called centripetal or centrifugal because there is no rotation. If you begin to spin the planet and keep increasing the speed of the rotation, those two forces will both lessen and reach zero when the object becomes weightless. Any analysis which asserts that a centrifugal force is going up as the rotation gets faster is working with an abstraction which does not represent what the real forces are doing. The gravitational force is constant until the object lifts off the ground, and the other real forces are both going down while the imaginary centrifugal force in the abstraction goes up.
Title: Re: What is centrifugal force?
Post by: rmolnav on 01/01/2019 11:36:55
An object sitting on a non-rotating planet will press down on the surface of the planet and a reactive force will be generated in the opposite direction to oppose it. Neither of those forces can be called centripetal or centrifugal because there is no rotation. If you begin to spin the planet and keep increasing the speed of the rotation, those two forces will both lessen and reach zero when the object becomes weightless. Any analysis which asserts that a centrifugal force is going up as the rotation gets faster is working with an abstraction which does not represent what the real forces are doing. The gravitational force is constant until the object lifts off the ground, and the other real forces are both going down while the imaginary centrifugal force in the abstraction goes up.
1) "Neither of those forces can be called centripetal or centrifugal because there is no rotation. If you begin to spin the planet and keep increasing the speed of the rotation ..." then the "reason" that there is no rotation would not apply, some force would have to function as centripetal force, and "inertial effects" would appear because massive stuff is being accelerated ...
2) "Any analysis which asserts that a centrifugal force is going up as the rotation gets faster is working with an abstraction which does not represent what the real forces are doing":
Wrong, as shown below.
3) "The gravitational force is constant until the object lifts off the ground, and the other real forces are both going down while the imaginary centrifugal force in the abstraction goes up".
Wrong ... Long before any of us could "levitate" on the equator, the equatorial bulge would get much, much bigger, and even, as I said:
 
Earth solid parts are stretched as in the CD case, and also would explode at much higher velocity.
And earth´s crust couldn´t deform so much, let alone break into pieces, without exerting on it strong opposite REAL forces, in our case centripetal forces (the ones which make earth stuff rotate at so high speed), and centrifugal forces (always due to inertia, or "reactive" as you say ...). 
Title: Re: What is centrifugal force?
Post by: David Cooper on 01/01/2019 20:26:34
then the "reason" that there is no rotation would not apply, some force would have to function as centripetal force, and "inertial effects" would appear because massive stuff is being accelerated ...

When you start the rotation, you can play games by renaming forces that were already acting before there was any rotation, but they go down in strength while your imagined centrifugal force goes up. Even if you're prepared to accept that these real forces go down instead and you decide to call one of them centrifugal, you would have to call it reactive centrifugal force, which is the only real kind of centrifugal force, acting in response to centripetal force and being equal to it. Then, at the point where the reactive centrifugal force reaches zero and the object becomes weightless, the centripetal force must also have reached zero, revealing that the gravitational force which you also like to call centripetal force in situations with orbiting objects is not the same as the centripetal force that was acting in the opposite direction to the reactive centripetal force that was present up until the object became weightless.

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2) "Any analysis which asserts that a centrifugal force is going up as the rotation gets faster is working with an abstraction which does not represent what the real forces are doing":
Wrong, as shown below.

Repeatedly claiming that correct things are wrong does not make them wrong.

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3) "The gravitational force is constant until the object lifts off the ground, and the other real forces are both going down while the imaginary centrifugal force in the abstraction goes up".
Wrong ... Long before any of us could "levitate" on the equator, the equatorial bulge would get much, much bigger...

If the bulge gets bigger, the real forces go down even more, but your imaginary centrifugal force in the maths of the abstraction rises more to match.

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, and even, as I said:
Earth solid parts are stretched as in the CD case, and also would explode at much higher velocity.
And earth´s crust couldn´t deform so much, let alone break into pieces, without exerting on it strong opposite REAL forces, in our case centripetal forces (the ones which make earth stuff rotate at so high speed), and centrifugal forces (always due to inertia, or "reactive" as you say ...). 

Trying to muddying the waters with other forces which bind material together isn't going to wash - you are trying to sell a force that doesn't exist, and I'm not buying it.
Title: Re: What is centrifugal force?
Post by: rmolnav on 07/01/2019 12:13:50
When you start the rotation, you can play games by renaming forces that were already acting before there was any rotation, but they go down in strength while your imagined centrifugal force goes up. Even if you're prepared to accept that these real forces go down instead and you decide to call one of them centrifugal, you would have to call it reactive centrifugal force, which is the only real kind of centrifugal force, acting in response to centripetal force and being equal to it. Then, at the point where the reactive centrifugal force reaches zero and the object becomes weightless, the centripetal force must also have reached zero, revealing that the gravitational force which you also like to call centripetal force in situations with orbiting objects is not the same as the centripetal force that was acting in the opposite direction to the reactive centripetal force that was present up until the object became weightless
With your last post one can tell you haven´t grasped what centripetal force actually is yet!!
As I´ve said many times, any rotation, or any movement of massive particles along a curved path, REQUIRES a net amount of centripetal force exerted on it, that can be provided by different sources … Otherwise, due to inertia the movement would be along a straight line at constant speed, whatever the way it initially got that speed ... That "simple" !!
The only detail not that simple is that FUNCTION as centripetal force can be exerted by either the total amount of a single force, or part of it (in size, or a certain fraction of one of its orthogonal components), or a combination of different forces …
Imaging a sling rotating in a vertical plane. When the string is horizontal, only its tension functions as centripetal force: gravity either increases or decreases linear velocity. But when at upper location gravity, added to string tension, functions as centripetal force, and our hand need not to pull down so much … if we wish to keep a constant angular speed (almost impossible though …). The opposite happens at lower position, because gravity is kind of centrifugal at that point, and string tension (necessarily much higher) minus gravity is what functions as centripetal force …
And at intermediate locations inward radial components of gravity vector, in each case with its sense, added to string tension, are which function as centripetal force.
What is much more complex is how the object continues to show its inertial "tendency" to follow straight, somehow opposing to the centripetal force which is "forcing" it to bend its path (certainly not always as a “real” centrifugal force). That depends on other details of the scenario, mainly on dynamic details such as grade and type of "freedom" the object has to "reply" acting centripetal force. 
You go from the "no rotation" scenario (gravity and internal forces do exist, but no centripetal force required), to an imaginary “perfect” orbiting situation (by the way, quite different scenario from the one I brought up), without considering any intermediate situation (the ONLY ones which could actually happen, as the current spinning at 2π radians/24 h angular speed).
By the way, you say:
... forces that were already acting before there was any rotation, but they go down in strength while your imagined centrifugal force goes up
Previously "acting forces" were gravity and internal compressive forces. Gravity, as a result of the stretching that causes the equatorial bulge, does decrease a little ... But required centripetal force (mω˛r) increases enormously, and bigger and bigger fraction of gravity pull has to function as centripetal force. And any inertial effect, such as centrifugal forces if any, increases more and more ... 
And you also say:
"... you can play games by renaming forces that were already acting before there was any rotation, ..."
It is not a question of "renaming": if earth starts spinning, inertia makes its particles try to follow a straight path (the tangent) ... Required centripetal force at each location only can come from gravity, and from internal interactions that are partially due to gravity ...
Curiously at earth solid core what happens is similar to "your" case of an object hanging from a string and a pole, made rotate with a bat: the material of the core, enormeosuly compressed due to gravity, if somehow made rotate, doesn´t let the particles to follow the tangent, and it gets radially stretched, what can provide the necessary increase of centripetal force: bigger and bigger fractions of gravitational forces (directly or indirectly) exert the FUNCTION of centripetal force.
From there to earth crust, the stuff is liquid, a quite different scenario ... Now it is like a centrifuge. Due to inertia, each particle tries to follow the tangent ... But earth crust doesn´t allow them to do so, and that induces an increase in pressure under earth crust. Initially earth´s crust and gravity provide the required centripetal force (exerted on the magma), and the magma exerts an equal but centrifugal force on the crust (as currently happens).
Own earth crust inertia also causes its deformation (inertial effects on lower latitude parts are much higher, and internal centrifugal forces appear), also tending to an earth equator diameter increase ... 
But at much higher angular speed earth´s crust can´t withstand all internal stresses caused that way, and would break into pieces (long before any "levitation" of outer objects).
By the way, "your" orbiting "weightless" object scenario would be also quite different from the case of a pair of comparable celestial objects rotating around their common center of mass, because that object wouldn´t affect earth dynamics (though theoretically would also exert an equal but opposite pull on earth, as inertial reaction according Newton´s 3rd Motion Law).
Title: Re: What is centrifugal force?
Post by: David Cooper on 07/01/2019 20:17:12
With your last post one can tell you haven´t grasped what centripetal force actually is yet!!

With your last post one can tell that your thinking is all over the place, leading to you failing to pin anything down. We're looking at a simple scenario here. We start with a planet with an object sitting on it and the planet not rotating. The planet pulls at the object, let's make it a 1kg rock, and the rock applies a compressive force which is resisted by a reactive force of equal strength in the opposite direction.

When we start to make the planet rotate (with the rock at the equator), that compressive force goes down, and so does the reactive force resisting it. The gravitational force remains almost the same, but it will go down a little as the equator bulges out a bit. That compressive force could now potentially be labelled as centripetal force and the reactive force opposing it would then be called reactive centrifugal force, though I don't know if science actually applies those labels to these forces in such a case.

The important point here though is that the imaginary centrifugal force which you're trying to sell is a (fake) force that goes up in strength as the planet rotates faster, and while it does this, the real forces go down - the rock presses down less hard and the ground has less to resist against. The gravitational force goes down a little as the equator bulges a fraction. No real force is going up, but your imaginary centrifugal force is growing stronger as the rotation speed goes up.

You keep attempting to keep this imaginary force as a real force by confusing people with other forces that do exist, applying incorrect names to them to pretend that some of them qualify as the kind of centrifugal force that doesn't exist. I don't know why you're playing such games. Maybe you're just so confused that you can't untangle it all and see the simple reality that lies beneath the unnecessary complexity that's blinding you.

When we get to the point where the rock becomes weightless, it is in orbit, even if it's still in contact with the ground. At this time, the rock is not pressing down on the planet and the ground is not pushing back, so even if you want to call those forces centripetal and reactive centrifugal, they are both down to zero. And now that the rock is in orbit, you want to call the entire gravitational force acting on it centripetal force, so it becomes clear that any attempt to call the compressive force centripetal is incompatible with this other kind of centripetal force that's now applying on the rock to hold it in orbit. Also, once the rock is in orbit, there is no centrifugal force in action - the only force there is the gravitational pull which you call centripetal. The imaginary centrifugal force that you want to assert is real here is just an artefact of the abstraction of analysing events using a rotating frame of reference - it isn't a real force. The existence of other forces that can be called centrifugal (and which should actually be called "reactive centrifugal force") are not evidence for the existence of the imaginary centrifugal force that you keep trying to sell.

This is why forces ought to be more carefully named to keep different kinds of force in separate compartments so that people are less likely to conflate them and come to incorrect conclusions.
Title: Re: What is centrifugal force?
Post by: rmolnav on 12/01/2019 11:09:28
And now that the rock is in orbit, you want to call the entire gravitational force acting on it centripetal force, so it becomes clear that any attempt to call the compressive force centripetal is incompatible with this other kind of centripetal force that's now applying on the rock to hold it in orbit. Also, once the rock is in orbit, there is no centrifugal force in action - the only force there is the gravitational pull which you call centripetal. The imaginary centrifugal force that you want to assert is real here ...
I was referring to what happens at different parts of our planet: the solid core, the liquid magma, and the crust, where real centrifugal forces, "reactive" if you like, do exist.
But you only refer to a loose rock on earth surface, reaching a "weightless" condition thanks to an enormous angular speed increase, something that would´t ever happen because earth crust would break up before, precisely due to above mentioned centrifugal forces, that previously would also have increased more and more the equatorial bulge size.
Nevertheless, in that particular  scenario, what you say "once the rock is in orbit, there is no centrifugal force in action" would be correct, but I´m afraid you don´t fully understand all the dynamic details of what happens, let alone what I say:
What is much more complex is how the object continues to show its inertial "tendency" to follow straight, somehow opposing to the centripetal force which is "forcing" it to bend its path (certainly not always as a “real” centrifugal force). That depends on other details of the scenario, mainly on dynamic details such as grade and type of "freedom" the object has to "reply" acting centripetal force.
.
And when the rock gets "weightless", it is orbiting around earth C.G. (at a fixed point), quite "free" to maintain its linear speed, and experiencing (the rock as a whole) only earth´s gravitational pull, perpendicular to its speed ...
That´s the "essence" of a circular, uniform movement. And the whole earth´s pull is what "forces" the rock to follow a circular path, instead of its natural, inertial tendency to keep constant its velocity vector.
That force is a centripetal force, by definition, not just the way I "want" to call it  ...
The "reply" of the stone to being "forced" that way, in this case is what I also said:
... that object (the rock) wouldn´t affect earth dynamics (though theoretically would also exert an equal but opposite pull on earth, as inertial reaction according Newton´s 3rd Motion Law)
and, on the one hand, if what the rock actually does is to "exert" that force, it couldn´t be considered a centrifugal force (though rock particles keep their "tendency" to "resist" given centripetal acceleration: if the surface were wet, water would move outwards, outdoing water surface tension). And on the other hand, as that force doesn´t affect earth´s dynamic whatsoever (as e.g. happens to the "couple" moon-earth), and the size of the rock is negligible, the case can be considered only as a "free" fall of the rock in a fixed gravitational field ...
Another thing would be if the hight of the rock were not negligible (compared to earth radius). In that case gravitational pull on each rock´s particle would clearly differ from required centripetal force at its location, and they wouldn´t actually be in a "proper" free fall ... Internal stresses (in pairs, centripetal and centrifugal) would appear to compensate those differences, stretching the rock radially.
(I do know you don´t agree with that, long discussed on the thread about tides, but I repeat it here for the sake of other possible readers ...)
As far as I can understand, what you say:
The important point here though is that the imaginary centrifugal force which you're trying to sell is a (fake) force that goes up in strength as the planet rotates faster, and while it does this, the real forces go down - the rock presses down less hard and the ground has less to resist against. The gravitational force goes down a little as the equator bulges a fraction. No real force is going up, but your imaginary centrifugal force is growing stronger as the rotation speed goes up.
is rather confusing.
At current angular speed (or other "intermediate" scenario), only a fraction of gravitational pull FUNCTIONS as centripetal force: just mω˛r ... And that fraction does increase with angular speed ...
As you say, " ... the rock presses down less hard and the ground has less to resist against". Please note that the difference is precisely that value (mω˛r), to satisfy Newton´s 2nd Motion Law. And the rest of gravitational pull keeps earth and rock pressing onto each other (not to be called centripetal or centrifugal forces, because, as said above, they are equal to the fraction of gravitational pull which DOESN´T cause any acceleration ...).
Those action and reaction "compressive" forces, though certainly due to gravity, shouldn´t be confused either with it or with part of it: gravitational pull is exerted between all earth´s and rock´s particles, and mentioned compressions are pushes interchanged by only the particles in contact ...

Title: Re: What is centrifugal force?
Post by: David Cooper on 12/01/2019 22:24:18
But you only refer to a loose rock on earth surface, reaching a "weightless" condition thanks to an enormous angular speed increase, something that would´t ever happen because earth crust would break up before, precisely due to above mentioned centrifugal forces, that previously would also have increased more and more the equatorial bulge size.

I referred to a planet rather than to the Earth, and I did so for a good reason. When dealing with thought experiments, the normal approach is to simplify things to remove all extraneous factors, and there's no call for them to be brought into it by someone who just wants to sow confusion. The planet in my thought experiment could be solid rock all the way through with no hot core, and rotation at the speed that will render the rock weightless would not break the planet up at all.

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Nevertheless, in that particular  scenario, what you say "once the rock is in orbit, there is no centrifugal force in action" would be correct, but I´m afraid you don´t fully understand all the dynamic details of what happens, let alone what I say:

I suspect I understand the dynamic details in considerably more depth than you do. What I'm doing is simplifying things down with thought experiments to remove the stuff that keeps confusing you and sending you off in the wrong direction. The equatorial bulge is not pushed out or held up by centrifugal force - that is the key point here.

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Another thing would be if the hight of the rock were not negligible (compared to earth radius). In that case gravitational pull on each rock´s particle would clearly differ from required centripetal force at its location, and they wouldn´t actually be in a "proper" free fall ... Internal stresses (in pairs, centripetal and centrifugal) would appear to compensate those differences, stretching the rock radially.
(I do know you don´t agree with that, long discussed on the thread about tides, but I repeat it here for the sake of other possible readers ...)

It's a diversion away from the issue in point. If you want to discuss stresses within the rock, discuss that in its own right and then work out what the forces are that are acting there. You won't find the imaginary kind of centrifugal force acting there either, but you might be able to justify calling one of them reactive centrifugal force.

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As far as I can understand, what you say:
The important point here though is that the imaginary centrifugal force which you're trying to sell is a (fake) force that goes up in strength as the planet rotates faster, and while it does this, the real forces go down - the rock presses down less hard and the ground has less to resist against. The gravitational force goes down a little as the equator bulges a fraction. No real force is going up, but your imaginary centrifugal force is growing stronger as the rotation speed goes up.
is rather confusing.
At current angular speed (or other "intermediate" scenario), only a fraction of gravitational pull FUNCTIONS as centripetal force: just mω˛r ... And that fraction does increase with angular speed ...
As you say, " ... the rock presses down less hard and the ground has less to resist against". Please note that the difference is precisely that value (mω˛r), to satisfy Newton´s 2nd Motion Law. And the rest of gravitational pull keeps earth and rock pressing onto each other (not to be called centripetal or centrifugal forces, because, as said above, they are equal to the fraction of gravitational pull which DOESN´T cause any acceleration ...).
Those action and reaction "compressive" forces, though certainly due to gravity, shouldn´t be confused either with it or with part of it: gravitational pull is exerted between all earth´s and rock´s particles, and mentioned compressions are pushes interchanged by only the particles in contact ...

Why are you confused by it? I was spelling out what the available forces are and showing you that centrifugal force (the kind that isn't reactive centrifugal force) doesn't come into play anywhere. Your centripetal force is an abstraction - you're attributing to centripetal force an increasing fraction of the gravitational force as the rotation speeds up, but the real gravitational force acting on the rock is either constant or is going down as the planet changes shape a little. That centripetal force is not opposed by any kind of centrifugal force. It therefore makes no sense to attribute the existence of the equatorial bulge to centrifugal force.
Title: Re: What is centrifugal force?
Post by: rmolnav on 22/01/2019 14:35:51
I have seen it expressed now and again that gravity is an invented power. That mysterious changes in geometry cause gravity. In this way I trust it is vital to nail down a definition.
I was going to  send a reply to quoted "mona2200" post of three days ago, but it has disappeared !! ??
Though gravity as an invented "power" sounds awful, I don´t think the post deserved removal ... After all, Einstein´s theory of curving of time-space, due to the presence of massive objects, as essence of gravity may be considered kind of "mysterious (?) changes in geometry" ...
Title: Re: What is centrifugal force?
Post by: rmolnav on 06/03/2019 11:41:52
Since my last post I´ve frequently found myself ruminating on our issue, trying to find better ways to convey my stand.
On this thread and on “Why do we have two high tides a day”, many times I´ve referred to the different ways inertia manifests itself, depending on the type and degree of “freedom” to move considered material stuff actually has …
The more I ruminate on the issue, the clearer I find that the root of the confusion is that the term “centrifugal force” is used too broadly, even in cases where certainly a “centrifugal effect” does exist, but not as a real newtonian force … But in other cases that centrifugal effect appears, totally or partially, as a real force.
A general term to cover all scenarios could be “centrifugal inertial effect” (CIE?), that always is present if the trajectory of any massive stuff is curved, whatever the cause of that curved path … I´ll try and elaborate as follows.
We all know Newton´s Motion Laws. But I´m afraid not all keep in mind those laws are just the consequence of the basic Physics phenomenon of INERTIA: massive objects (and any part of them) always have a TENDENCY to maintain constant its current velocity vector, and they show a RESISTANCE to any agent trying to accelerate considered massive stuff. Those laws put it in terms of forces: f=ma (2nd law), being 1st law when f=0, and 3rd one the necessary consequence when considering two directly interacting objects.
We can analyze any possible case starting directly from INERTIA phenomenon, instead of using the “tool” of Newton´s Laws, not breeching them though: it´s a kind of other side of the coin …
In some cases, that RESISTANCE shows up as a real FORCE, but certainly not always.
The term CENTRIFUGAL always refers to an outward “tendency” to move, implying the existence of a “center”: the center of a circular path followed by an object, or at least the center of curvature of its CURVED PATH.
It´s convenient to separate cases with direct physical connection between interacting objects (A), from cases when gravity is involved (B).
A) Hammer throwing: the “hammer”, as a whole, is being centripetally accelerated. INERTIA tends to make it go on the tangent, the cable (and the athlete) don´t let it move straight, and the inertial RESISTANCE to being accelerated inwards appears as a real CENTRIFUGAL FORCE exerted by the hammer on the wire´s end … (I´m not considering now internal forces, that would be different if we had a sling instead, and form a “field” of real centrifugal forces, exerted between contiguous particles …).
It´s what David Cooper calls “reactive centrifugal force”. Similar things can be said about other cases such as wheeled wagons on a railway, vehicle rubber tires on road surface (with or without banking), etc., 
B) When gravity is involved, as it changes with distance, it´s paramount to distinguish cases when those changes are practically null (due to the rotating object negligible size, compared with distance to the object causing the gravitational field - e.g.: artificial satellites), from the rest.
B.1) In the first case the objects are in a pure “free fall”. All their particles are accelerated the same. Inertial RESISTANCE to being accelerated (proportional to mass and given acceleration) is precisely what makes necessary the existence of the gravitational pull f=ma: otherwise the object would continue straight.
But now we don´t have even a “reactive” centrifugal force: acting centripetal force, the gravitational pull at that location, is independent from the object´s inertia … If in some moment F were not equal to ma, the object would be free to change orbit (certainly a case quite different from hammer-throwing).
B.2) The simplest case is our moon rotation around earth-moon barycenter.
INERTIA makes every moon´s particle tend to keep moving straight, but all those particles are forced to follow circular paths.
The further the particle, the bigger the radius, and the bigger the acting centripetal force mω˛r.
Inertial RESISTANCE to being accelerated is proportional to ma. If the particles were in a real free fall, they would be free to adjust their orbits to the acting gravitational pull at their location, that varies inversely to the square of the distance.
But that is not possible. If, e.g., we transversely “cut” the moon into too halves, the further one is being centripetally accelerated more than what earth´s pull would cause on that “hemimoon” if it were really free to move. Therefore, ALWAYS existing inertial RESISTANCE to being accelerated is only PARTIALLY compensated by earth´s gravitational pull, the unique force “external” to the moon. That fraction of that inertial RESISTANCE, as on case B.1, doesn´t cause any additional centrifugal effect, let alone force.
But the inertial RESISTANCE not “compensated” that way is still present, and, similarly to what in the hammer throwing case (A), it causes an outward pull on adjacent inner half moon. That is a real CENTRIFUGAL FORCE, quite similar to the one exerted by the hammer on the wire´s end. It “forces” closer half of the moon to keep the common orbit, instead of a smaller one that would match with the stronger earth´s pull on closer “hemimoon”.
On any other transverse section similar things happen, and the moon is stretched in the direction of the straight line earth-moon, what is also called “tidal effect”. By the way, directly connected with the fact that the moon is “tidal locked” to earth (closer and further mentioned halves don´t change, apart from some very tiny “oscillation”).
So, I consider quite opposite stands:
1) In all cases with curved paths real centrifugal forces are present,
2) The fact of having a curved path doesn´t imply the existence of real centrifugal "effects", and real centrifugal forces only appear in cases similar to hammer throwing (never when gravity is involved),
are both erroneous.
And the "invention" of a fictitious centrifugal force for cases when a rotating frame of reference is used doesn´t help diminish confusion ... That just adds something to cause the REAL inertial effects that, logically, disappear when rotation "ceases", as actually happens relatively to mentioned type of frame (precisely called "non inertial" !!).   

Title: Re: What is centrifugal force?
Post by: David Cooper on 06/03/2019 23:08:20
But the inertial RESISTANCE not “compensated” that way is still present, and, similarly to what in the hammer throwing case (A), it causes an outward pull on adjacent inner half moon. That is a real CENTRIFUGAL FORCE, quite similar to the one exerted by the hammer on the wire´s end. It “forces” closer half of the moon to keep the common orbit, instead of a smaller one that would match with the stronger earth´s pull on closer “hemimoon”.

If we think about an object sitting near a black hole, the gravity pulls on the object, and it does so more strongly on the near side of that object than the far side, so a tension force appears within it (which might pull it apart in the process known as spaghettification). That tension force is not any kind of centrifugal force. That force will be opposed by an opposite force which is likewise not any kind of centrifugal force.

If the planet is going round the black hole rather than falling towards it, these opposed tension forces are still acting within it, but their cause is exactly the same as in the non-rotating case. If you want to call the gravitational force centripetal force, what are you going to call the tension force that acts in the same direction? Is it centripetal force too? Maybe it is - it's just the force being converted to a different from and transferred on, so yes, and that logically requires you to call the opposing tension force reactive centrifugal force.

However, all these forces are driven by direct gravitational pull and the rotation aspect is a complete irrelevance to them, so if you want to provide people with a real understanding of what's going on, you have a duty to avoid using words like centripetal and centrifugal in the explanation.
Title: Re: What is centrifugal force?
Post by: rmolnav on 07/03/2019 12:29:08
the gravity pulls on the object, and it does so more strongly on the near side of that object than the far side, so a tension force appears within it (which might pull it apart in the process known as spaghettification). That tension force is not any kind of centrifugal force. That force will be opposed by an opposite force which is likewise not any kind of centrifugal force.
After many months of "dynamical" discussion, you keep not considering the real phenomenon of INERTIA, as if it didn´t exist, and therefore ignoring its "effects" ...
If it didn´t exist, the different pulls (because of the different distances) you talk about wouldn´t be able to generate any "opposite force" and cause spagettification. In that kind of impossible case, the object would get an "average" acceleration (though that is also directly connected to the phenomenon of inertia) ...
What actually causes the "opposite force" is the fact that the smaller pull on far side of the object is insufficient to "balance" inertial "resistance" to accelerate there that much. If a particle there were really "free", it would accelerate less. But the inertial resistance of the particle to accelerate is proportional to the acceleration actually given to it.
That difference between external pull on a particle, and inertial "resistance" to accelerate more than f/ma, is actually the appearing "opposite force". 
As I´ve said many times, far side particles have no way to "know" how much near particles are pulled, let alone how to "calculate" any difference between pulls on distant particles, to react accordingly !!
But all particles "feel" external gravitational pull at their location, and kind of internal inertial "resistance" to beeing accelerated, what, if not in balance, causes a real "opposite force" (exerted by the particle on adjacent particles, as the hammer on the wire) ...
And, as I´ve also said many times, that inertial effect is due to exactly the same reason as in cases were the movement is not along a straight line, but along a curved path ...
The only difference is that on curved ones, gravitational pull and relevant accelerations have not the same direction as the object velocity ... Due to that, the gravitational pull (or at least its component perpendicular to actual velocity vector), ACTING as centripetal force, causes the velocity vector change direction ...
And, similarly to the straight line case, the object offers an inertial "resistance" to being centripetally accelerated, what if not in balance with actual gravitational pull on the particle (e.g., ma>f), equally causes an "opposite force". And a force opposite to a centripetal force is, logically, a centrifugal force !!
But in the straight line case forces and accelerations have not any kind of relation with curved movements, necessary for the existence of the concept of centripetal forces, centripetal accelerations, and centrifugal forces, and where a "center" of curvature does exist ...   
Title: Re: What is centrifugal force?
Post by: David Cooper on 07/03/2019 21:05:06
After many months of "dynamical" discussion, you keep not considering the real phenomenon of INERTIA, as if it didn´t exist, and therefore ignoring its "effects" ...

Inertia is tied up in everything I've said. Things keep moving (or not moving) in the same way so long as there's no force being applied to them. When you apply a gravitational force to them and that force is stronger at one end than the other, the nearest end is pulled more strongly than the far end and you get a tension force appearing in the object. I have no problem with you using the word inertia as a result and have never objected to it.

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As I´ve said many times, far side particles have no way to "know" how much near particles are pulled, let alone how to "calculate" any difference between pulls on distant particles, to react accordingly !!

Who needs the particles to know anything? They simply continue to move as they are already moving unless a force is applied to them, whether that's through gravitational pull or by a more local pull or push from adjacent material.

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The only difference is that on curved ones, gravitational pull and relevant accelerations have not the same direction as the object velocity ... Due to that, the gravitational pull (or at least its component perpendicular to actual velocity vector), ACTING as centripetal force, causes the velocity vector change direction ...

The only change to the movement is along the direction in which the force is applied.

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And, similarly to the straight line case, the object offers an inertial "resistance" to being centripetally accelerated, what if not in balance with actual gravitational pull on the particle (e.g., ma>f), equally causes an "opposite force". And a force opposite to a centripetal force is, logically, a centrifugal force !!

In any case where the force is still acting when the orbital movement is removed, the use of the word "centripetal" was misleading, no matter how firmly established that usage of the word is in science. It is when we stop the object and see that the forces continue to operate in full that we realise that they are not genuinely centripetal because they are still fully in play while the label is no longer valid in any way. That is how you get to a better scientific understanding - you look for the places where your labels break and then you realise that you are dealing with something more fundamental. With something going round on a string, the centripetal and reactive centrifugal labels don't break when you remove the orbital movement because the forces disappear - they genuinely are generated by the rotational movement.
Title: Re: What is centrifugal force?
Post by: rmolnav on 08/03/2019 12:15:43
It would be utterly absurd (and useless) we to continue here our so long last summer and fall discussion on thread "Why do we have two high tides a day?" ...
But, for the sake of the possible interest of other readers, I´m going to put here something directly related to what you are saying now, root of your erroneous stand, as far as I can understand:
In any case where the force is still acting when the orbital movement is removed, the use of the word "centripetal" was misleading, no matter how firmly established that usage of the word is in science. It is when we stop the object and see that the forces continue to operate in full that we realise that they are not genuinely centripetal because they are still fully in play while the label is no longer valid in any way. That is how you get to a better scientific understanding - you look for the places where your labels break and then you realise that you are dealing with something more fundamental.
I´ve said here time and time again that "centripetal force" is neither an "essentially" new force, nor just a  label we can give any force "at will" !! It is just a FUNCTION, which many essentially different types of forces can EXERT, if they are causing the bending of the trajectory of a moving object ...
A pilot, after landing the airplane and going home, is not EXERTING as pilot whatsoever ... Do you consider we should not "label" him or her as a "pilot" because we "are dealing with something more fundamental" (a human being) ??
With something going round on a string, the centripetal and reactive centrifugal labels don't break when you remove the orbital movement because the forces disappear - they genuinely are generated by the rotational movement.
Many times I´ve told you that is erroneous ... Movement doesn´t actually "generate" forces, the opposite occurs !!
You say "With something going round on a string" ... ?? What follows comes from our last year discussion of that case, if the initial movement were caused hitting the ball with a bat.
Hitting a ball produces a transference of momentum, through forces as always. At the very initial instant some deformations (of the ball and the bat) occur, what produces opposite pushes on each other, which then change both speed vectors … The ball gets a speed, and its inertia tries to make it go straight … If a string attached to a pole prevent that to happen, an initial string tension has to exist for that to occur (otherwise the ball would continue straight). That initial string tension is already an initial centripetal force. What the ball´s inertia does (though only over a very short time) is to further tighten the string, and that means the centripetal force increases (exerted by the string on the ball), and subsequently centrifugal “reactive" force (exerted by the ball on the string) also increases …
The initially rectilinear movement is logically necessary to get it converted into a circular one, but it isn´t actually the cause of of that “conversion” and occurring forces … An independent initial tension of the string is required, that could be called “initial centripetal force” as soon as the rectilinear path changes into curved one (not exactly circular at the beginning, because the elasticity of the string, and the fact that initially could´t be fully tight …). And its further increase, and also increasing centrifugal forces, are not directly caused by the initial rectilinear movement, but a consequence of ball´s inertia, manifesting itself that way after the ball being “forced” to bend its path by initial string tension, initial centripetal force ...
 
Title: Re: What is centrifugal force?
Post by: David Cooper on 08/03/2019 19:50:17
I´ve said here time and time again that "centripetal force" is neither an "essentially" new force, nor just a  label we can give any force "at will" !! It is just a FUNCTION, which many essentially different types of forces can EXERT, if they are causing the bending of the trajectory of a moving object ...

All I'm asking you to do is distinguish between the different cases and to make clear that when you're dealing with the gravitational cases, the orbital aspect is not generating the forces that are being being applied, while in the case of something going round on the end of a wire, the orbital aspect is generating the forces. That is something you're still refusing to do. Stop the ball on the string by absorbing all the energy that's making it move perpendicular to the string and the tension forces in the wire disappear. Do the same with a ball orbiting a planet and the forces continue to act in full. I don't know why you're incapable of agreeing with that, but something is blocking your thinking on that point, and you would gain a lot by fixing it.

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Many times I´ve told you that is erroneous ... Movement doesn´t actually "generate" forces, the opposite occurs !!

And every time you've been wrong. All you need to do is trace the cause and effect order of events. The tension in the string never causes the object on the end of it to start moving round in circles, and cutting the string to remove that tension does not make the ball stop. It is starting the ball moving that generates the tension in the string and stopping the ball that removes the tension in it. No amount of elaborating on the components of these actions can change that - the big picture remains as I have stated it.
Title: Re: What is centrifugal force?
Post by: rmolnav on 09/03/2019 12:29:07
I repeat: it would be useless to repeat here our past year discussion on the other thread ... But:
 
The tension in the string never causes the object on the end of it to start moving round in circles, and cutting the string to remove that tension does not make the ball stop.
I never said the tension makes the object "start moving round in circles" ... But if an object initially in rectilinear movement start being pulled perpendicularly to its velocity vector, the movement CHANGES into a curved one, whatever the way it is pulled (string, gravity, road/tyre friction, etc).
That force is always what is "accelerating" the object inwards, and CAUSES the movement to be circular (or just curved), instead of rectilinear.
And it is called CENTRIPETAL FORCE by any physicist you may find, whatever your "problems" with the term, certainly a "great area" for you as you said long ago ...
Title: Re: What is centrifugal force?
Post by: David Cooper on 09/03/2019 22:58:56
I never said the tension makes the object "start moving round in circles" ...

Of course you didn't, but that is the necessary conclusion if you put the causation the wrong way round by denying that the perpendicular movement causes the tension rather than the reverse. The perpendicular movement of the object is a crucial cause of the centripetal force the string. In the gravity case, the perpendicular movement has zero role in causing the the gravitational force that's being labelled as "centripetal force". This is a key difference between the two cases, and any attempt to explain what happens in gravitational cases through the use of the words centripetal or centrifugal are misleading, implying that the rotation has a role, whereas in reality it is the straight-line gravitational pull that provides the true explanation with no causal input from the rotation. I don't know why you're so unwilling to accept that reality.

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And it is called CENTRIPETAL FORCE by any physicist you may find, whatever your "problems" with the term, certainly a "great area" for you as you said long ago ...

[Grey area; not great.]

The way they use the term is unhelpful, but at least most of them recognise the difference between the two cases rather than being blinded by words. They accept that straight-line gravitational pull is the better explanation and that there is no centrifugal mechanism behind tidal bulges of any kind.
Title: Re: What is centrifugal force?
Post by: rmolnav on 11/03/2019 11:06:53
Quote from: rmolnav on Yesterday at 12:29:07
I never said the tension makes the object "start moving round in circles" ...
Of course you didn't, but that is the necessary conclusion if you put the causation the wrong way round by denying that the perpendicular movement causes the tension rather than the reverse. The perpendicular movement of the object is a crucial cause of the centripetal force the string
I repeat: WRONG.
The "perpendicular movement" is obviously a necessary initial condition for the rotation to start, but:
1) An independent initial tension is also a necessary condition ...
2) That initial tension has to pull perpendicularly the object (initial centripetal force), what initiates the curving of the object´s path ... Otherwise the object would continue moving straight.
3) That "triggers" a chain of action and reaction forces ...
4) First reaction of the object is to pull outwards (centrifugally) the string´s outer end (3rd Newton´s Motion Law) ...
5) That increases the tension of the string, what also increases centripetal force and subsequently the centrifugal inertial reaction exerted by the object on the string´s end ...
6) And so on ...
The movement cannot "magically" cause any force by itself ... It is inertia, the "resistance" of the object to change its velocity vector, what can show up as a reactive force ... But for that to happen, as said above, an initial and independent centripetal "action" force is absolutely necessary. Otherwise the object would continue moving straight (1st Newton´s Motion Law)
In any case, that bizarre case imagined by you is a short-life one … To make the object go on turning it´d be necessary that initial independent centripetal force to last longer, e.g. with the inner string end being pulled by a hammer thrower, a case not that different from earth revolving around earth-moon barycenter, always in opposition to moon´s location … The athlete has also to lean back to “compensate” inertial centrifugal reaction of the weight, that is being “forced” to follow a curved path, rather than moving straight.
There are certainly differences, but I´m not going to refer to them now, because I did it recently (#233, 235, 237 and 239).
You don´t agree? ... Well, I have to accept it. But don´t expect to convince me that, just because gravity exists even without any object´s movement, there are no inertial centrifugal "effects" when the object is continuously  changing its velocity vector´s direction ...(due to gravitational pull, ACTING as centripetal force).
As said on mentioned posts, those effects vary depending on the degree and "type" of freedom every affected particle actually has. But they do exist.
Title: Re: What is centrifugal force?
Post by: David Cooper on 11/03/2019 19:20:40
I repeat: WRONG.

No amount of repeating that will make you right.

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1) An independent initial tension is also a necessary condition ...

No it isn't. The line can be slack. Once you add the perpendicular movement, the tension is produced. When the perpendicular movement is removed, the tension disappears from the line and it goes slack again. That shows very clearly the the order of causation. There is no equivalent of this in the gravity cases - the force acts continuously regardless of any perpendicular movement as there is no causal connection between the two.

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2) ... 6) And so on ...

And you're just going through the components again in a futile attempt to change the reality of the big picture. No amount of picking through the parts will change the causation where the perpendicular movement has a key role in generating the tension in the string (and where it does not generate the gravitational force in the gravity case at all).

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But don´t expect to convince me that, just because gravity exists even without any object´s movement, there are no inertial centrifugal "effects" when the object is continuously  changing its velocity vector´s direction ...(due to gravitational pull, ACTING as centripetal force).
As said on mentioned posts, those effects vary depending on the degree and "type" of freedom every affected particle actually has. But they do exist.

The whole point is that your imagined centrifugal effects don't exist in the gravity case. The perpendicular movement has zero role in flinging up a tidal bulge.
Title: Re: What is centrifugal force?
Post by: rmolnav on 13/03/2019 08:28:40
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1) An independent initial tension is also a necessary condition ...
No it isn't. The line can be slack. Once you add the perpendicular movement, the tension is produced. When the perpendicular movement is removed, the tension disappears from the line and it goes slack again. That shows very clearly the the order of causation.
WRONG! You talk about " add the perpendicular movement", and "When the perpendicular movement is removed" ... How do you "imagine" those actions could actually be realized ?? Because you don´t even mention Newton´s Motion Laws I referred to, that ALWAYS must be accomplished, as far as movement is concerned ...
When the line is “slack” as you say, its end is supposedly still. And at a certain moment there is a physical transference of momentum (or kinetic energy, if you prefer) between the two “objects” in contact: the ball and the string hook.
As I´ve said several times, the hook and string end ONLY can be put in motion with an external force, because the ball cannot directly “deliver” any type of energy or momentum as if it were a kind of commodity …
In an initial instant ∂t, if we consider m the average of moved mass of hook and string end, f=ma (1st Newton´s Motion Law).
That force ONLY can be exerted by the ball, and it “comes” from its energy. But for that transformation to happen, part of the ball´s energy has to be transferred to the hook, what happens via impulse I, according to the relation:
I = f ∂t = m ∂v,
Over same instant dif.t, the momentum of the ball decreases also in that amount (the speed inversely to ball´s mass).
From that it can be deduced that same force f, but opposite, is being exerted by the hook on the ball (3rd Newton´s Motion Law). But, though apparently the “primary” force is exerted by the ball on the hook (by the "movement" as you say), that´s not so. Without an initial reduction of the ball´s velocity, part of its momentum couldn´t have been transferred to the hook. And that ball´s momentum reduction requires the force exerted by the hook on the ball initiate the transference of momentum. 
So far, all mentioned vectors, in bold letters (velocity, acceleration, force, momentum and impulse) are in the same direction of initial ball velocity. Without any other initial force with not null component perpendicular to those vectors, both ball and hook would continue moving straight in that direction …
ONLY with an initial tension of the string, the rectilinear movement can change and get curved. Now also 1st Newton´s Motion applies, but with force and acceleration vectors in the direction of the string (perpendicular to above mentioned vectors).
And, after that, all steps I listed on a couple of days ago post occur:
"2) That initial tension has to pull perpendicularly the object (initial centripetal force), what initiates the curving of the object´s path ... Otherwise the object would continue moving straight.
3) That "triggers" a chain of action and reaction forces ...
4) First reaction of the object is to pull outwards (centrifugally) the string´s outer end (3rd Newton´s Motion Law) ...
5) That increases the tension of the string, what also increases centripetal force and subsequently the centrifugal inertial reaction exerted by the object on the string´s end ...
6) And so on ..."
Do you know better than Newton, or do you interprete his Motion Laws differently ?? If so, please kindly don´t just say my interpretation is wrong, and give all of us some explanation with formulas (not just things such as "if you add the movement ..." !!).
The whole point is that your imagined centrifugal effects don't exist in the gravity case. The perpendicular movement has zero role in flinging up a tidal bulge.
Also WRONG.
Many, you included, say only differential gravity can cause tidal bulges …
Let us imagine moon´s gravity were constant across the earth, maintaining moon´s total pull, and therefore actual distances and moon-earth “dancing” …
The “tendency” of earth revolving particles (both solid and water) not to change their velocity vectors (INERTIA) would cause two “tidal” bulges, but BOTH in the sense opposite to the moon (opposite to the centripetal force, that is, always parallel to line earth C.M. - barycenter - moon C.M.).
That implies that the sublunar “bulge” would actually be the opposite: earth radius decreases at that hemisphere …
That would be similar to what happens if, with our hands, we make a cap of tea on a table follow uniformly a circular path …
As I´ve said on "Why do we have two high tides a day?" thread many times, those centrifugal inertial "effects", added to what caused directly by the varying gravitational moon´s pull (inversely proportional to the square of the distance), is what causes the real tidal bulges !!
Remember what Einstein thought:
"Einstein warmed to the idea that the gravitational field of the rest of the Universe might explain centrifugal and other inertial forces resulting from acceleration".
Do you know better than Einstein ?? Or do you think that gravitational pull, acting as centripetal force (by the way, your "grey" area ...) doesn´t cause centripetal acceleration, and subsequently neither centrifugal forces nor other inertial "effects" are present ??
If so, please kindly give all of us your "reasons", instead of just saying "your imagined centrifugal effects don't exist in the gravity case"
Title: Re: What is centrifugal force?
Post by: David Cooper on 14/03/2019 00:11:42
WRONG! You talk about " add the perpendicular movement", and "When the perpendicular movement is removed" ... How do you "imagine" those actions could actually be realized ??

In the case of a ball on the end of a string (let's have this floating in space and going round a pole with huge masses on either end), a bat can be used to start it going round and to stop it moving. In the case of a ball orbiting an asteroid, a bat can be used to stop the orbital movement, and to start it again if there isn't too long a delay before doing this (because it will fall towards the asteroid).

Why do you find it so hard to think up a practical experiment of this kind to illustrate what you somehow imagine to be an impossibility? It took me about five seconds of thinking time to construct those two examples. But you shouldn't even be asking me to realise them when we're dealing with principles which still apply in the case of a moon going round a planet where we can't make a bat big enough to do the same job - the impossibility of making an adequate bat for that does not negate the principle. Stop shouting "WRONG" at people and sort out your incorrect position instead of assuming it's not you that's got it wrong.

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Because you don´t even mention Newton´s Motion Laws I referred to, that ALWAYS must be accomplished, as far as movement is concerned ...

Newtons laws are on my side. Relativity (all versions) are on my side too. I don't need to drag names in to boost a rock-solid argument.

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When the line is “slack” as you say, its end is supposedly still. And at a certain moment there is a physical transference of momentum (or kinetic energy, if you prefer) between the two “objects” in contact: the ball and the string hook.
As I´ve said several times, the hook and string end ONLY can be put in motion with an external force, because the ball cannot directly “deliver” any type of energy or momentum as if it were a kind of commodity …

The ball is floating in space and the string is slack. I hit the ball in a direction perpendicular to the string. The ball tries to move in a straight line and pulls on the string, and that pull generates the centripetal force in the string. The reactive centrifugal force in this case isn't so much reactive as a causitive force, but relativity blurs the difference in any case. We don't need to care, because these forces result from the ball moving as a result of being hit by the bat. That is all that matters - we are comparing this with the ball sitting near the asteroid (and falling towards it) which, if we hit it with the bat to produce an orbit for it, that hit did not generate or trigger into existence in any way shape or form the gravitational force that is coming from the asteroid. That force was already acting. These are the facts, and no amount of dissecting the components of the action will reverse these facts. The case is closed.

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Do you know better than Newton...

If Newton agrees with you, tell him to join the forum and to state which side he's on.

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Also WRONG.

Someone's sold you a faulty dictionary. The word you should be using is "right".

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Let us imagine moon´s gravity were constant across the earth, maintaining moon´s total pull, and therefore actual distances and moon-earth “dancing” …

An evenly applied force where each atom of the Earth is pulled equally. Lovely.

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The “tendency” of earth revolving particles (both solid and water) not to change their velocity vectors (INERTIA) would cause two “tidal” bulges, but BOTH in the sense opposite to the moon (opposite to the centripetal force, that is, always parallel to line earth C.M. - barycenter - moon C.M.).

An evenly applied force of this kind would move the whole Earth without producing any bulges on it whatsoever. That's why we don't get tidal bulges from the strongest pull on us which comes from the galaxy - its pull is stronger than the sun's and the sun's is stronger than the moon's, but it is so evenly applied that we see no effects on the Earth's shape.

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As I´ve said on "Why do we have two high tides a day?" thread many times, those centrifugal inertial "effects", added to what caused directly by the varying gravitational moon´s pull (inversely proportional to the square of the distance), is what causes the real tidal bulges !!

Stop using the word centrifugal. It's misleading. All we have is different parts of the Earth being pulled towards the moon with different strengths, leading to some trying to move faster than others and the whole thing attempting to elongate. One bulge is from the material being pulled towards the moon most strongly, while the other bulge is from the material being pulled least strongly lagging behind. That is it. It works in a straight line system with no orbit exactly as it does in an equivalent system with an orbit - the orbit is irrelevant.

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Remember what Einstein thought:

If Einstein agrees with you, tell him to join the forum and to state which side he's on.

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Do you know better than Einstein ??

If he disagrees with me on this, then yes, but I don't think he will. Bring him here and let's find out.

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Or do you think that gravitational pull, acting as centripetal force (by the way, your "grey" area ...) doesn´t cause centripetal acceleration, and subsequently neither centrifugal forces nor other inertial "effects" are present ??
If so, please kindly give all of us your "reasons", instead of just saying "your imagined centrifugal effects don't exist in the gravity case"[/b]

You've had my reasons and they prove the case in multiple ways. You do not have any centrifugal force building any bulges anywhere at all in these gravity cases, and you don't even have it building any bulges in cases with a string because even when there is reactive centrifugal force in play, it's pulling the wrong way, limiting the amount of bulge rather than driving the bulge.
Title: Re: What is centrifugal force?
Post by: rmolnav on 15/03/2019 12:25:26
Since long ago, time and time again, I´ve seen it is useless to discuss with you, at least on dynamics, because you kind of feel 100 % sure of something ONLY if it is what you think you see in nature, forgetting that in milliseconds many things can happen, impossible for our eyes to see ...
When I once asked you for references supporting some of your ideas, you yourself said (thread "Why do we have two high tides a day", #184):
"I am always more interested in actual science than error-ridden authorities. I haven't seen anyone in science support my position (primarily because I haven't looked for that) - what I'm saying is based 100% on what I see when I look directly at the physics involved in this !!!”.
No wonder now, after me saying what quoted below, instead of giving us any alternative scientific explanation (with formulas "converting" physical variables and functions into others, as far as "movement" and forces are concerned):
the hook and string end ONLY can be put in motion with an external force, because the ball cannot directly “deliver” any type of energy or momentum as if it were a kind of commodity …
In an initial instant ∂t, if we consider m the average of moved mass of hook and string end, f=ma (1st Newton´s Motion Law).
That force ONLY can be exerted by the ball, and it “comes” from its energy. But for that transformation to happen, part of the ball´s energy has to be transferred to the hook, what happens via impulse I, according to the relation:
I = f ∂t = m ∂v,
Over same instant dif.t, the momentum of the ball decreases also in that amount (the speed inversely to ball´s mass).
From that it can be deduced that same force f, but opposite, is being exerted by the hook on the ball (3rd Newton´s Motion Law). But, though apparently the “primary” force is exerted by the ball on the hook (by the "movement" as you say), that´s not so. Without an initial reduction of the ball´s velocity, part of its momentum couldn´t have been transferred to the hook. And that ball´s momentum reduction requires the force exerted by the hook on the ball initiate the transference of momentum. 
you now just say:
Newtons laws are on my side
and try to explain us the experiment imagined by you, apparently supporting your stand, in a quite "layman" way ...
Newton stated that the direct cause of movement (acceleration that initiates a movement, or modifies its velocity vector), is ALWAYS a force (external to the object). He also considered a force can directly be caused by another force (as inertial reaction), but he never said what you say, e.g. that a movement can "generate" (?) a force, let alone what you said on mentioned #184:
"If a force is generated by rotation, that is clearly centripetal force - a force that comes into play because of the rotation ...” !!!
You seem to want to change Physics science, at least Dynamics, because I also gave you references such as:
"- Univ. of Ohio ( "phisics.ohio-state.edu”, "Dynamics of Uniform Circular Motion" (Chapter 5, 5.3 Centripetal Force).
- Univ. of Louisville (Centripetal Force - Physics 298 - Department of Physics and Astronomy, www.physics.louisville.edu/cldavis/phys298/notes/centripetal.html 
- Several Physics academies, mentioned on my post # 413.
- Merriam Webster dictionary (“movement”, “to move”, “force”…)
- Oxford dictionary (“centripetal force”) 
among others",
but you keep stuck to your ideas ...
Either you explain them "scientifically", not just telling us what you "see" in nature, or in experiments imagined by you in five seconds (!!):
Why do you find it so hard to think up a practical experiment of this kind to illustrate what you somehow imagine to be an impossibility? It took me about five seconds of thinking time to construct those two examples
or, sorry, your ideas can´t be taken seriously ...
If you did some real experiment in a lab, with modern hardware (at least a camera able to take thousands of pictures in a second), and appropriate software, the results would shed light on the issue, and you could see who is right and who is wrong ...
 
Title: Re: What is centrifugal force?
Post by: David Cooper on 15/03/2019 23:03:16
Since long ago, time and time again, I´ve seen it is useless to discuss with you, at least on dynamics, because you kind of feel 100 % sure of something ONLY if it is what you think you see in nature, forgetting that in milliseconds many things can happen, impossible for our eyes to see ...

You can chop a dog into as many components as you like, but you will never be able to prove it's a cat. It remains a dog.

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No wonder now, after me saying what quoted below, instead of giving us any alternative scientific explanation (with formulas "converting" physical variables and functions into others, as far as "movement" and forces are concerned):

I'm not going to waste my time dissecting a dog to prove it's a dog to someone who's adamant that it's a cat.

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Newton stated that the direct cause of movement (acceleration that initiates a movement, or modifies its velocity vector), is ALWAYS a force (external to the object). He also considered a force can directly be caused by another force (as inertial reaction), but he never said what you say, e.g. that a movement can "generate" (?) a force, let alone what you said on mentioned #184:
"If a force is generated by rotation, that is clearly centripetal force - a force that comes into play because of the rotation ...” !!!

I can't help it if you can't find the right thing to quote from Newton or if he never spelt out what is happening in a case like this one. If a force can only be caused by another force, two objects that are moving towards each other will be unable to produce any impact forces when they collide because you demand that a force can only be caused by a force.
 
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You seem to want to change Physics science, at least Dynamics, because I also gave you references such as:
...
but you keep stuck to your ideas ...

I'm sticking to ideas that are right, whereas all you're doing is looking for anything you can take out of context to support your errors (or anything you can find where a scientist has made the same errors).

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Either you explain them "scientifically", not just telling us what you "see" in nature, or in experiments imagined by you in five seconds (!!):
Why do you find it so hard to think up a practical experiment of this kind to illustrate what you somehow imagine to be an impossibility? It took me about five seconds of thinking time to construct those two examples
or, sorry, your ideas can´t be taken seriously ...

Oh, sure they can't - it would be impossible for a ball to orbit an asteroid because we've never put a ball in orbit round an asteroid, and because we've never done it, it must be impossible to stop it going round the asteroid by hitting it with a bat. That's essentially your argument. I say it can be done though. Science gives us universal principles which allow us to predict how things will behave, and in this case it gives us every confidence that if we were to put a ball in orbit round an asteroid (which isn't even very far from something we have already done with space probes visiting asteroids), it would go round the asteroid and could be stopped by hitting it with a bat, whereupon it would accelerated down onto the asteroid because the gravitational force is still being applied to it in full.

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If you did some real experiment in a lab, with modern hardware (at least a camera able to take thousands of pictures in a second), and appropriate software, the results would shed light on the issue, and you could see who is right and who is wrong ...

You want to do the experiment in a lab with a ball orbiting an asteroid? I hope you've got an antigravity machine to stop the Earth's gravity wrecking the experiment. How have you managed to shackle your thinking abilities in such an extreme way that you can't imagine the interactions between simple things like a bat hitting a ball?

The other case was a ball on a string, which again I had to ask you to do in space to stop you obsessing about the Earth's gravity interfering when the ball's stopped by the bat. The ball is stopped and the string goes slack. Do it on the Earth and it doesn't go slack for long because gravity pulls the ball downwards - we're then dealing with a mixed gravity and string case instead of looking at a pure string case, which is what you ought to be capable of considering. In the pure string case though where we aren't messing it up with gravity, when the bat stops the ball, the string goes slack.

But you don't want to consider this case because it hasn't been done in space, and therefore my description must be bad science, just like the bad science which people relied on when sending people to the moon by calculating what would happen and then acting on the assumption that the laws of nature wouldn't let them down. It worked, and my thought experiments will work for real too if they're ever tried. If anyone thinks they won't, please name yourself in a reply so that we can see how many people have the same beliefs as rmolnav.
Title: Re: What is centrifugal force?
Post by: rmolnav on 17/03/2019 11:41:43
You can chop a dog into as many components as you like, but you will never be able to prove it's a cat. It remains a dog.
Right !
I'm not going to waste my time dissecting a dog to prove it's a dog to someone who's adamant that it's a cat.
WRONG ... because what I "dissected" was TIME, a second into milliseconds, and never said those milliseconds are not TIME any more ...
And however good vision you might have, you would´t notice physical, real things that happen in milliseconds !!
You initially see and object moving, afterwards you see forces that didn´t exist before ... and you conclude thinking something as if you were a child (or a non-educated adult): the movement is what "generates" the forces ...
And you dare say Logics is your speciality !!
Sorry, but as I´ve said many times, it´s useless to discuss with you ... If I have done it for so long, it has been for the sake of any other reader who could be interested.
 
You want to do the experiment in a lab with a ball orbiting an asteroid?
What an absurd way of misunderstanding my words !! I said:
"If you did SOME real experiment in a lab ... "[/quote]
and, logically, I referred to the pole-string-ball case, or something similar.
With suitably placed gauging devices, ultra high-speed camera, and appropriate software, we could see forces building up ("reacting" to other previous "action" force interchanged between the two objects in contact), but ALWAYS starting with an initial force exerted by the string ...
If that initial force didn´t exist at all, nothing could start braking the moving object, what is absolutely necessary for any transference of momentum !!
Remember:
the hook and string end ONLY can be put in motion with an external force, because the ball cannot directly “deliver” any type of energy or momentum as if it were a kind of commodity …
In an initial instant ∂t, if we consider m the average of moved mass of hook and string end, f=ma (1st Newton´s Motion Law).
That force ONLY can be exerted by the ball, and it “comes” from its energy. But for that transformation to happen, part of the ball´s energy has to be transferred to the hook, what happens via impulse I, according to the relation:
I = f ∂t = m ∂v,
Over same instant dif.t, the momentum of the ball decreases also in that amount (the speed inversely to ball´s mass).
From that it can be deduced that same force f, but opposite, is being exerted by the hook on the ball (3rd Newton´s Motion Law). But, though apparently the “primary” force is exerted by the ball on the hook (by the "movement" as you say), that´s not so. Without an initial reduction of the ball´s velocity, part of its momentum couldn´t have been transferred to the hook. And that ball´s momentum reduction requires the force exerted by the hook on the ball initiate the transference of momentum. 
That fully agrees with Newton´s Motion Laws ...
You consider movement can also directly "cause" forces, and once you even said there is a "symmetry" ... Could you please give us Motion Laws "symmetric" to Newton´s, which could allow us explain the case (with affected physical variables, functions and formulas, not just "literature" ? 
Title: Re: What is centrifugal force?
Post by: David Cooper on 17/03/2019 22:24:09
WRONG ... because what I "dissected" was TIME, a second into milliseconds, and never said those milliseconds are not TIME any more ...

The dog is the big picture in which stopping the ball moving causes the centripetal and reactive centrifugal force in the string to disappear and where starting the ball moving again (perpendicular to the string) causes those forces to reappear. The dog is the big picture in which when you stop the ball in the gravity case, the asteroid  continues to apply its gravitational pull on it in full.

The cat is an alternative picture in which stopping the ball moving doesn't cause the centripetal and reactive centrifugal force in the string to disappear and where starting the ball moving again (perpendicular to the string) doesn't cause those forces to reappear. The cat is incompatible with the universe.

Dissecting the dog will never turn it into a cat.

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And however good vision you might have, you would´t notice physical, real things that happen in milliseconds !!

I'm not missing any momentary cat. It's always a dog.

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You initially see and object moving, afterwards you see forces that didn´t exist before ... and you conclude thinking something as if you were a child (or a non-educated adult): the movement is what "generates" the forces ...
And you dare say Logics is your speciality !!

No, my conclusion is the kind that a scientist comes up with. Yours is a complete inversion of science.

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Sorry, but as I´ve said many times, it´s useless to discuss with you ... If I have done it for so long, it has been for the sake of any other reader who could be interested.

You have gone on doing it because you still can't see that you're wrong. It is certainly interesting to watch you and wonder how you manage to go on being so wrong though.

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What an absurd way of misunderstanding my words !! I said:
"If you did SOME real experiment in a lab ... "

And in doing so, you deny the validity of the fully sound thought experiments which you're trying to discredit on the basis that they haven't been done for real in a lab.

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and, logically, I referred to the pole-string-ball case, or something similar.
With suitably placed gauging devices, ultra high-speed camera, and appropriate software, we could see forces building up ("reacting" to other previous "action" force interchanged between the two objects in contact),

There is no disagreement here about the forces building up over time and the possibility of cutting the dog into tiny slices to see that play out, but it doesn't turn it into a cat.

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but ALWAYS starting with an initial force exerted by the string ...
If that initial force didn´t exist at all, nothing could start braking the moving object, what is absolutely necessary for any transference of momentum !!

How does it start with an initial force exerted by the string? The first force is applied to the string by the ball as the ball tries to follow a path that would require the string to lengthen if no force was to be generated.The perpendicular movement of the ball ceases to be perpendicular to the string after a moment of movement because the other end of the string and the ball aren't co-moving. This means the movement of the ball is now in a direction that applies a force to the string - its movement generates that force. We're dissecting the dog here and it is not turning into a cat. If it was a cat, we would magically start with a force springing out of nothing in the string, and that force would then cause the ball to move perpendicular to the string. But we are most certainly not dealing with a cat.

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But, though apparently the “primary” force is exerted by the ball on the hook (by the "movement" as you say), that´s not so. Without an initial reduction of the ball´s velocity, part of its momentum couldn´t have been transferred to the hook. And that ball´s momentum reduction requires the force exerted by the hook on the ball initiate the transference of momentum.

There is room to argue about which force acts first to drive the other, but these rival forces are centripetal and reactive centrifugal forces. Relativity allows you to have them both play an equal role (i.e. to be equally first), but it also allows either one to drive the other. None of that is of any importance to our discussion though - it remains the dissection of a dog. What drives the generation of BOTH of those forces is the movement of the ball relative to the thing at the opposite end of the string, and we can call that thing at the other end of the string an anchor (on the basis that the string is anchored to something). When they are not moving relative to each other, there is no force in the string. When we start moving the ball relative to the anchor and perpendicular to the string, or if we start moving the anchor relative to the ball and perpendicular to the string, that generates the two forces in the string as soon as the movement ceases to be perpendicular. This is not a moggy. In the moggy, you want to have the forces act in the string first, and then you want either the ball or anchor to start moving as a result, but that is bonkers science. Real science works the other way round - the perpendicular movement of ball or anchor (or both) generates the forces in the string (and if we dissect the dog a little, this happens because the movement relative to the string doesn't remaining perpendicular until the forces are generated in the string to force the movement to remain perpendicular).

Woof!
Title: Re: What is centrifugal force?
Post by: rmolnav on 19/03/2019 08:04:36
A lot of "literature" on last post, but no scientific explanation of how on earth movement of an object can "cause" and a force on another ...
If there is a symmetry as D.C. says, it should be possible to have "motion --> force" laws, kind of symmetric to "force --> motion" Newton´s Laws.I haven´t seen them anywhere, I asked D.C. for them, but business as usual ...
Leaving aside the tricky case pole-string-object, I´ll go back to a gravitational scenario, to have yet another go.
Remembering the “famous” case of the three balls, let us make it simpler and consider just two, in straight line with a much more massive object exerting gravitational pull on them (for the sake of simplicity, let us consider negligible the gravitational pull between the two balls).
On each ball  ONLY the gravitational pull at its location is exerted, and they, completely free to move, are being accelerated, back one less because the pull is smaller there. That makes them separate more and more.
Inertial “resistance” to accelerate (tendency to keep their velocity constant), proportional to mass and actually given acceleration, is just “overcome” by gravity pull, and they accelerate “without any problem” …
We could “refer" the movement of one of them relatively to the other (non-inertial reference system), and say back one accelerates “backwards”, though only relatively to the other … I would understand even the use of the term “differential acceleration” …
But the term “differential gravity” would be absurd, because the “difference” between the two real pulls is not a force actually exerted anywhere, it is something only exists in our minds, as I´ve said many times. When, e.g., at the beginning of a competition, a bike accelerates more than another, we can say there is a  “differential acceleration”, that can be directly observed and even measured. But the terms “differential thrust” of the engines, and the thrust of one "relatively" to the other, would have no sense at all ...
But if mentioned balls are stuck together, they aren´t free to move: they are somehow “forced” to accelerate the same, despite the different gravitational pulls exerted on them …
Forward ball is being accelerated less than what gravity there would cause if it were “independent” to move … Inertial resistance to accelerate is smaller than actual gravitational pull … A “spare” forward force remains acting on it.
The opposite happens to backward ball: it is being accelerated more than what gravity there would cause if the ball were completely free to move … Inertial resistance to accelerate is bigger than actual gravitational pull … A “spare” backward inertial force acts on it.
Those two opposite forces, directly exerted on the balls (by the way, not the case of anything like the so called “differential gravity”), stretch the two-part "object", a clear “tidal” effect, using the adjective in its broad sense.
It would be utterly absurd to think mentioned backward force could be called “centrifugal force”, because in that one-dimension scenario there isn´t a proper “center”. The same could be said about the term “centripetal force”.
But if the two balls also had an initial velocity perpendicular to the straight line going from them to the object causing the gravity, resulting movement would be a curved one, and mentioned stretch would also happen, exactly for the same reasons ...
In that case of circular (or at least curved) movement, both centripetal and centrifugal force terms are the correct ones used in Physics, though “centrifugal” one certainly not by everybody ...
And please kindly note that closer ball is forcing (pulling) further one to experience an acceleration additional to the one directly caused by gravity, in that case by “contact”, same way as in the string case the hook pulls inwards (centripetally) the rotating, “hooked” object.
And, again, when gravitational pull exerts the FUNCTION of centripetal force, logically it doesn´t change the ESSENCE of it ...
And, also logically, if tangential velocity is somehow reduced to null, that FUNCTION disappears, because we are in a different scenario, the one-dimension exposed above ("centripetal" adjective should be substituted by "forward", and "centrifugal" by "backward").
And the fact that gravity remains even if the "perpendicular" movement is somehow removed doesn´t mean that to call its previously existing FUNCTION as centripetal is erroneous, as D.C. has as kind of "life motive" ... (no wonder D.C. says "centripetal force" concept is a "grey area").
If with initial "perpendicular" movement, the gravity would be somehow switched off, the balls would continue its straight path ... That means gravitational pull (or at least a part of it), when existing, is what causes the curved movement, though initial "tangential" speed, logically again, is a necessary condition.


Title: Re: What is centrifugal force?
Post by: David Cooper on 19/03/2019 22:58:54
A lot of "literature" on last post, but no scientific explanation of how on earth movement of an object can "cause" and a force on another ...

Apart from the scientific explanation I provided (which you simply ignore).

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If there is a symmetry as D.C. says, it should be possible to have "motion --> force" laws, kind of symmetric to "force --> motion" Newton´s Laws.I haven´t seen them anywhere, I asked D.C. for them, but business as usual ...

Imagine that you are drifting in deep space and that you have a ball on a long coiled string with the other end tied onto you. You throw the ball away from yourself, the string is pulled out by the ball, and when it reaches its full length, a strong tension force is suddenly generated in it. If the movement of the ball (relative to you) isn't responsible for generating that tension force, what is? Magic? I say that the movement generates the force (once the movement is resisted by the string). If there is no movement in a case like this, there will never be a force in the string.

When you run a reversible event backwards, the causation reverses too. If I drop a weight on a spring it may cause the spring to compress. The spring may then rebound and fling the weight off it. The movement of the weight causes the spring to compress and a force to be generated which halts the weight while energy is stored in the spring. The spring then releases that energy back and generates a force which accelerates the weight upwards, this force causing weight to move again. Every step in that process is governed by a rule that future parts of the action do not cause parts in their past, but that the causation operates from past to future. Perhaps this was so obvious that Newton didn't think it worth mentioning, but you can be sure that he fully understood it to be the case.

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But the term “differential gravity” would be absurd, because the “difference” between the two real pulls is not a force actually exerted anywhere, it is something only exists in our minds, as I´ve said many times.

There is a pull on each ball, and a difference between the strength of those pulls. It is not something that merely exists in the mind (unless we're applying a theory of gravity in which it is not a force).

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But the terms “differential thrust” of the engines, and the thrust of one "relatively" to the other, would have no sense at all ...

What's the problem with that? If they're putting out different amounts of thrust, that description sounds fully apt.

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But if mentioned balls are stuck together, they aren´t free to move: they are somehow “forced” to accelerate the same, despite the different gravitational pulls exerted on them …

...which means that the different pulls on each will generate tension forces which resist the stretching.

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The opposite happens to backward ball: it is being accelerated more than what gravity there would cause if the ball were completely free to move … Inertial resistance to accelerate is bigger than actual gravitational pull … A “spare” backward inertial force acts on it.

The only forces acting on it are gravity, pulling it towards the massive object, and the tension force from the ball nearer to the massive object. There is no force pulling the further out ball outwards. The only force pulling outwards is the tension force acting on the inner ball, and that is resisting the stretch.

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Those two opposite forces, directly exerted on the balls (by the way, not the case of anything like the so called “differential gravity”), stretch the two-part "object", a clear “tidal” effect, using the adjective in its broad sense.

The actual forces in the object are trying to arrest that stretch; not drive it.

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It would be utterly absurd to think mentioned backward force could be called “centrifugal force”, because in that one-dimension scenario there isn´t a proper “center”. The same could be said about the term “centripetal force”.
But if the two balls also had an initial velocity perpendicular to the straight line going from them to the object causing the gravity, resulting movement would be a curved one, and mentioned stretch would also happen, exactly for the same reasons ...

The stretch is caused solely by the nearer ball being pulled more strongly towards the massive object than the other ball. That is what is applying the stretch. The other forces that are generated in the object are both opposing that stretch. The perpendicular movement makes no difference to the forces in play, as you can tell when you apply relativity to this.

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In that case of circular (or at least curved) movement, both centripetal and centrifugal force terms are the correct ones used in Physics, though “centrifugal” one certainly not by everybody ...

You need to see past the official correctness of the usage of terms to the actual causes and effects, and to the actual forces that are involved and their actual roles. The only cases where we've found any real force that can legitimately have "centrifugal" used as part of part of its name has that force act in the wrong direction to drive the generation of bulges.

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And please kindly note that closer ball is forcing (pulling) further one to experience an acceleration additional to the one directly caused by gravity, in that case by “contact”, same way as in the string case the hook pulls inwards (centripetally) the rotating, “hooked” object.

Yes, kindly note that it is pulling in such a way as to suppress the forming of a bulge, as is the force opposing it.

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And, again, when gravitational pull exerts the FUNCTION of centripetal force, logically it doesn´t change the ESSENCE of it ...

When there is no orbit, the force is the same strength at a given distance as when there is no orbital movement. The force is simply gravitational pull. Playing games where you call it centripetal in some cases and not in others illustrates that they are mere games, but even when you play those games, there are no centrifugal forces anywhere building bulges. The only real centrifugal force is reactive centrifugal force, and it always acts to suppress bulges.

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And, also logically, if tangential velocity is somehow reduced to null, that FUNCTION disappears, because we are in a different scenario, the one-dimension exposed above ("centripetal" adjective should be substituted by "forward", and "centrifugal" by "backward").

The "forward" force is pulling on the outer ball while the "backward" force is pulling on the inner ball, so these forces are pulling the balls towards each other. They are not friends of your argument at all.

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And the fact that gravity remains even if the "perpendicular" movement is somehow removed doesn´t mean that to call its previously existing FUNCTION as centripetal is erroneous, as D.C. has as kind of "life motive" ... (no wonder D.C. says "centripetal force" concept is a "grey area").

It's a grey area because we have two radically different cases. With the string, we have a centripetal force (and reactive centrifugal force opposing it) which ceases to exist when the orbital motion is removed, so there is deeper, more fundamental name for it. In the gravity case though, there is a deeper, more fundamental name for it, and that is gravity, and removing the orbital movement also shows that the correct name for the force is gravity because it remains in play when the word centripetal disappears from it without any loss of the force. That tells you what the force really is.

You could argue that the force in the string is an acceleration force both in cases where there's a acceleration in a straight line and where there's orbital motion, and thereby claim that there is no force that's fundamentally a centripetal force in that case either because it's actually an acceleration force, and then you could argue that gravity is an acceleration force too, so the word centripetal is equally valid in both cases. You haven't argued that, but I've just done that work for you. Does it help your case though? No. The only reason this line of thought has been followed at all was to try to get through to you that in gravity cases there is no centrifugal force opposing the gravity, which makes it different from the string case in which there's a reactive centripetal force opposing the centripetal force. You scored a significant point though when you pointed out that forces like those in string are in play within a ball even in the gravity case, but those forces oppose the stretching rather than driving it, and it turns out that the reactive centrifugal force in the string case opposes the stretching too. There is never a centrifugal force of any kind feeding into the formation of a tidal bulge or any equivalent bulge on a distorted ball on the end of a string.

You seek to find centrifugal forces that help to build bulges, but they always do the opposite. The only real centrifugal force is a reactive centrifugal force which tries to pull things outwards that are further in (such as the outer ball pulling the inner ball), thereby suppressing the formation of bulges. Reactive centrifugal force thus helps to pull the inner tidal bulge down, and that's an outward pull away from the source of the gravitational pull from the other body, so this is a case of a real centrifugal force pulling something outwards, but it isn't outwards in relation to the body where this pull is acting - it's an inward pull locally.
Title: Re: What is centrifugal force?
Post by: rmolnav on 26/03/2019 07:30:07
I haven´t replied last D.C. post so far to give other possible readers time to read it quietly.
I hope some have already done , and seen at least some of its persistent errors …
Now I´m going to refer to some of them, all at the very root of D.C.´s “grey” flawed stand.

A) You only refer to Newton when saying:
... a rule that future parts of the action do not cause parts in their past, but that the causation operates from past to future. Perhaps this was so obvious that Newton didn't think it worth mentioning, but you can be sure that he fully understood it to be the case
But I´ve never said Newton didn´t mention that ... ("causation operates from past to future") ... What Newton never said, as far as I know, is that movements, by themselves, can cause forces. He delivered his Motion Rules, stating forces cause accelerations. Therefore, they are absolutely necessary, both to initiate a movement, or to change its velocity vector …
“Your” artificial pole-string-object case and similar cases are far-fetched and uncommon, but natural collisions aren´t rare at all … How could Newton “forget" to analyze what (according to you) happens in those cases, that motion cause forces, and somehow include the results in his Motion Laws ?? Impossible to me.     
As I´ve already said, neither momentum nor kinetic energy are a kind of commodity, directly transferable when a collision or similar cases (such as when the string gets tight). An "exchage currency" is necessary, and it is called impulse. To start that “transference”, in an infinitesimal amount of time the momentum of the moving object HAS TO BE REDUCED by an external force, according to:
I = F∂t = ma∂t = m∂v.
That force, depending on each particular case, might be an initial latent force, a string own weight component, static friction, initial material resistance to deformations, etc.
The fact that it is not clearly visible to our eyes doesn´t mean it doesn´t exist … Otherwise the moving object would keep constant its velocity vector (Newton´s 1st Motion Law), and no transference of any momentum could occur !! 
 As a REACTION to that force (Newton´s 3rd Motion Law), the moving object starts exerting an equal but opposite force on the “obstacle” (string or initially still object). And a “chain” of mutual actions and reactions, in milliseconds, massively raise those opposite forces exerted on each other, what  changes velocities …

B) Many other ther errors are basically same error repeated many times !!:
B1)
The only forces acting on it are gravity, pulling it towards the massive object, and the tension force from the ball nearer to the massive object. There is no force pulling the further out ball outwards. The only force pulling outwards is the tension force acting on the inner ball, and that is resisting the stretch.
I´m afraid you haven´t fully grasped what a stretching actually is ... The "pairs" of opposite internal forces which "resist" the stretch logically are inwards (relative to the object, or the two stuck balls in our case). But that´s a clear evidence that some other forces are pulling outwards on both balls, and causing the stretch !!
In the two-ball case, one of the forces is gravitational pull on "forward" ball. The other is not so clearly visible when with only two "objects". But if we imagin "behind" ball cut into transverse slices, every slice is being pulled back by its neighbor, and each one is being stretched by its two next-door neighbors, what works in the sense of forming the further bulge …
Logically what you say also happens: through each section between two contiguous slices, they are pulling each other in the sense of “resisting” the stretch … But that is a kind of “the other side of the coin” !!
B2)
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Those two opposite forces, directly exerted on the balls (by the way, not the case of anything like the so called “differential gravity”), stretch the two-part "object", a clear “tidal” effect, using the adjective in its broad sense.
The actual forces in the object are trying to arrest that stretch; not drive it.
Same comment on B1) applies.
B3)
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But if mentioned balls are stuck together, they aren´t free to move: they are somehow “forced” to accelerate the same, despite the different gravitational pulls exerted on them …
...which means that the different pulls on each will generate tension forces which resist the stretching.
... which means that the different pulls on each (two pulls, each one applied on different locations - not a "differential pull" applied we don´t know where), together with the fact that those pulls don´t match with actual accelerations (what brings up inertial forces),  will stretch the whole.
Regarding material reactions, comment on B1) also applies.
B4)
The stretch is caused solely by the nearer ball being pulled more strongly towards the massive object than the other ball. That is what is applying the stretch. The other forces that are generated in the object are both opposing that stretch
Same comment on B1) applies.
There are some more paragraphs we could comment on similarly ...
C5)
The perpendicular movement makes no difference to the forces in play
.
A movement, even if not "perpendicular", certainly doesn´t directly affect forces … The opposite happens (Newton´s Motion Laws).
But that curved movement has both a velocity ("perpendicular") to forces in play, and also an acceleration, in line with forces in play ...
And you stubbornly (and blindly) keep saying things such as:
In the gravity case though, there is a deeper, more fundamental name for it, and that is gravity, and removing the orbital movement also shows that the correct name for the force is gravity because it remains in play when the word centripetal disappears from it without any loss of the force. That tells you what the force really is.
As far as I can remember, trying to make you see your Logics (and Physics) error, I´ve brought up two analogies so far:
- Donald Trump is "more deeply and fundamentally" a man, a human being ... Do you think we shouldn´t say he is also the President of USA, as if his FUNCTION didn´t exist ??
- The same with an airplane pilot, which also is "more deeply and fundamentally” a human being (ESSENCE), but when flying FUNCTIONS as a pilot.
But to no avail ...
If a moving object follows a curved path (whatever the causes), in an infinitesimal period of time ∂t its velocity vector v changes to v + ∂v ... That infinitesimal increase of velocity vector ∂v divided by the time ∂t is, BY DEFINITION, the acceleration vector of the movement at that point and instant ...
That acceleration HAS TO BE CAUSED by a force (Newton´s 1st Motion Law), exactly F = ma (Newton´s 2nd Motion Law).
For the sake of simplicity, let us suppose the size of the velocity vector keeps constant. In that case acceleration and causing force are perpendicular to the curved trajectory, and, also BY DEFINITION, they get the adjective CENTRIPETAL.
And the force exerting that FUNCTION of "bending" the trajectory, among several other ESSENCIALY different forces, can perfectly be gravity ...
If you don´t change some of your "chips", in particular if you stubbornly keep not accepting that centripetal character (FUNCTION) and its gravitational ESSENCE are quite compatible, you will keep drawing erroneous conclusions (by the way, the same will happen if you keep thinking Newton forgot to deliver "motion --> force" laws)  !!
We could even call that force, during the period mentioned function exists, "gravi-centripetal force" …
And, keeping “centripetal force” in your “grey area” that way, logically makes impossible for you even to just "imagine" the possibility that a CENTRIFUGAL force, (an inertial force requiring the existence of centripetal acceleration and forces), could exist in those cases !!
Title: Re: What is centrifugal force?
Post by: David Cooper on 26/03/2019 20:34:01
I haven´t replied last D.C. post so far to give other possible readers time to read it quietly.
I hope some have already done , and seen at least some of its persistent errors …
Now I´m going to refer to some of them, all at the very root of D.C.´s “grey” flawed stand.

And that's where I've stopped reading your post. I doubt anyone is reading it any more and I don't see why I should keep wasting more and more time doing so either. If anyone ever does read the rest of your latest post though and thinks there's something worthwhile in it, perhaps they can comment to alert others to the miracle.