What is centrifugal force?

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Offline jerrygg38

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What is centrifugal force?
« 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?

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Offline alancalverd

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Re: What is centrifugal force?
« Reply #1 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.
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Offline jerrygg38

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Re: What is centrifugal force?
« Reply #2 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?

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Offline Colin2B

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Re: What is centrifugal force?
« Reply #3 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.
and the misguided shall lead the gullible,
the feebleminded have inherited the earth.

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Offline jeffreyH

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Re: What is centrifugal force?
« Reply #4 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?
Fixation on the Einstein papers is a good definition of OCD.

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Offline jerrygg38

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Re: What is centrifugal force?
« Reply #5 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?

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Offline PhysBang

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Re: What is centrifugal force?
« Reply #6 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.

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Offline jeffreyH

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Re: What is centrifugal force?
« Reply #7 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.
Fixation on the Einstein papers is a good definition of OCD.

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Offline jerrygg38

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Re: What is centrifugal force?
« Reply #8 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.

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Offline alancalverd

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Re: What is centrifugal force?
« Reply #9 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.
« Last Edit: 20/08/2016 00:26:07 by alancalverd »
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Offline jerrygg38

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Re: What is centrifugal force?
« Reply #10 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.

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Offline puppypower

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Re: What is centrifugal force?
« Reply #11 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.

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Offline jerrygg38

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Re: What is centrifugal force?
« Reply #12 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.

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Offline PhysBang

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Re: What is centrifugal force?
« Reply #13 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.

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Offline PhysBang

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Re: What is centrifugal force?
« Reply #14 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.

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Offline jeffreyH

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Re: What is centrifugal force?
« Reply #15 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?
Fixation on the Einstein papers is a good definition of OCD.

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Offline PhysBang

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Re: What is centrifugal force?
« Reply #16 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.

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Offline jeffreyH

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Re: What is centrifugal force?
« Reply #17 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.
Fixation on the Einstein papers is a good definition of OCD.

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Offline PhysBang

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Re: What is centrifugal force?
« Reply #18 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.

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Offline jeffreyH

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Re: What is centrifugal force?
« Reply #19 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.
Fixation on the Einstein papers is a good definition of OCD.

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Offline jerrygg38

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Re: What is centrifugal force?
« Reply #20 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!

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Offline hamdani yusuf

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Re: What is centrifugal force?
« Reply #21 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.
Unexpected results come from false assumptions.

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Offline PmbPhy

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Re: What is centrifugal force?
« Reply #22 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

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Offline jerrygg38

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Re: What is centrifugal force?
« Reply #23 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.
 

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Offline jerrygg38

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Re: What is centrifugal force?
« Reply #24 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?

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Offline hamdani yusuf

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Re: What is centrifugal force?
« Reply #25 on: 24/08/2016 15:09:04 »
We don't feel earth rotation because it is too slow for our senses.
Unexpected results come from false assumptions.

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Offline alancalverd

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Re: What is centrifugal force?
« Reply #26 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.
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Offline jerrygg38

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Re: What is centrifugal force?
« Reply #27 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.

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #28 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)

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #29 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.

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Offline hamdani yusuf

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Re: What is centrifugal force?
« Reply #30 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?
Unexpected results come from false assumptions.

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #31 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.

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #32 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) 

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Offline hamdani yusuf

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Re: What is centrifugal force?
« Reply #33 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.
Unexpected results come from false assumptions.

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #34 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 doesnīt mean, as others say, that centrifugal force doesnīt 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 doesnīt change our arguments.   

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Offline puppypower

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Re: What is centrifugal force?
« Reply #35 on: 06/10/2016 11:20:29 »
Is the centrifugal force active in all rotations, from electron to galaxy rotation?

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #36 on: 07/10/2016 11:03:56 »
#35
Yesterday I sent a reply, but it is not here! I donīt 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, donīt 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.

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #37 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 donīt 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 didnīt 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"

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Offline hamdani yusuf

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Re: What is centrifugal force?
« Reply #38 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.
Unexpected results come from false assumptions.

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Offline jeffreyH

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Re: What is centrifugal force?
« Reply #39 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.
Fixation on the Einstein papers is a good definition of OCD.

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #40 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 dynamometerīs outer side, and forces could be gauged.
 
 

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #41 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 doesīn requires any, but with "a pull" I put "from" in opposite senses. Iīll 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 canīt 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 Newtonīs 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 ...

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #42 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 (!!)

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #43 on: 09/10/2016 13:38:57 »
#42 (continuation)
Sorry, "only" in the order of  1,000 times, instead of 10,000 !!

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #44 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 Iīm 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 Iīll do it another day/days, most probably in more than one step.
Now, as a kind of divertimento, Iīll 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.

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Offline alancalverd

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Re: What is centrifugal force?
« Reply #45 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.
helping to stem the tide of ignorance

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #46 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 isnīt actually a real force ...
There is a big confusion about this subject out there. Even between some scientists (!!).
Iīm seeing you are very active on many subjects, but not on either of the two mentioned.
Perhaps you have not seen what Iīm referring to. Otherwise you would have sent several refuting replies ...

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #47 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 canīt 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.

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #48 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.

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Offline hamdani yusuf

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Re: What is centrifugal force?
« Reply #49 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 doesīn requires any, but with "a pull" I put "from" in opposite senses. Iīll 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 canīt 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 Newtonīs 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?


Where is the centrifugal force in the first and second picture above?
Unexpected results come from false assumptions.