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### Author Topic: What is centrifugal force?  (Read 7592 times)

#### Nilak

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##### Re: What is centrifugal force?
« Reply #50 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.

#### rmolnav

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##### Re: What is centrifugal force?
« Reply #51 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.

#### rmolnav

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##### Re: What is centrifugal force?
« Reply #52 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.

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#### Nilak

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##### Re: What is centrifugal force?
« Reply #53 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.

#### hamdani yusuf

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##### Re: What is centrifugal force?
« Reply #54 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?

#### Nilak

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##### Re: What is centrifugal force?
« Reply #55 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.

#### rmolnav

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##### Re: What is centrifugal force?
« Reply #56 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

#### rmolnav

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##### Re: What is centrifugal force?
« Reply #57 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.

#### rmolnav

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##### Re: What is centrifugal force?
« Reply #58 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 !!)

#### rmolnav

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##### Re: What is centrifugal force?
« Reply #59 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

#### rmolnav

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##### Re: What is centrifugal force?
« Reply #60 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.

#### hamdani yusuf

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##### Re: What is centrifugal force?
« Reply #61 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.

#### rmolnav

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##### Re: What is centrifugal force?
« Reply #62 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.

#### hamdani yusuf

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##### Re: What is centrifugal force?
« Reply #63 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?

#### rmolnav

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##### Re: What is centrifugal force?
« Reply #64 on: 17/10/2016 19:29:17 »
#63 hamdani yusuf
« on: Today at 04:29:08 » Quote (selected):
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.
"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.

#### hamdani yusuf

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##### Re: What is centrifugal force?
« Reply #65 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.

#### puppypower

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##### Re: What is centrifugal force?
« Reply #66 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.

#### rmolnav

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##### Re: What is centrifugal force?
« Reply #67 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 ...

#### hamdani yusuf

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##### Re: What is centrifugal force?
« Reply #68 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?

#### rmolnav

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##### Re: What is centrifugal force?
« Reply #69 on: 18/10/2016 19:48:35 »
#68 hamdani yusuf
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.

#### hamdani yusuf

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##### Re: What is centrifugal force?
« Reply #70 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.

#### rmolnav

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##### Re: What is centrifugal force?
« Reply #71 on: 19/10/2016 12:17:19 »
#70
Wikipedia is not always completely right. Even it has errors.
“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?

#### rmolnav

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##### Re: What is centrifugal force?
« Reply #72 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

#### hamdani yusuf

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##### Re: What is centrifugal force?
« Reply #73 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.
« Last Edit: 19/10/2016 23:18:43 by hamdani yusuf »

#### rmolnav

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##### Re: What is centrifugal force?
« Reply #74 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.

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##### Re: What is centrifugal force?
« Reply #74 on: 20/10/2016 11:12:34 »