# The Naked Scientists Forum

### Author Topic: What is centrifugal force?  (Read 7655 times)

#### 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.

#### 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.

#### 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.

#### 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)

#### 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.

#### 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?

#### 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.

#### 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)

#### 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.

#### 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.

#### 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?

#### 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.

#### 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"

#### 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.

#### 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.

#### 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.

#### 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 ...

#### 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 (!!)

#### 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 !!

#### 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.

#### 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.

#### 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 ...
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 ...

#### 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.

#### 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.

#### 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?

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##### Re: What is centrifugal force?
« Reply #49 on: 13/10/2016 05:40:48 »