# What is a centrifugal force?

## Main Question or Discussion Point

What is a centrifugal force? Is it a pseudo force?

Does it really exist?.. Maybe i am not getting the idea of what a pseudo force is...

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What is a centrifugal force?
The centrifugal force is an outward-directed inertial force exerted on a body when it moves azimuthally in a noninertial rotating reference frame.
Is it a pseudo force?
Some scientists use that term to refer to inertial forces. However this is not universally used since some scientists consider inertial forces to be real (whatever that means).
Does it really exist?
Can't say unless you first tell us what you mean by "real"? As Ray D'Inverno wrote in his GR text The status of inertial forces is again a controversial one. In my opinion is is quite real. A good example is the following

http://www.whoi.edu/science/PO/people/jprice/class/aCt.pdf

For other examples of physicists with the same opinion consider the following:

From Newtonian Mechanics, A.P. French, The M.I.T. Introductory Physics Series, W.W. Norton Pub. , (1971) , page 499. After describing the inertial force as seen from an accelerating frame of reference French writes
From the standpoint of an observer in the accelerating frame, the inertial force is actually present. If one took steps to keep an object "at rest" in S', by tying it down with springs, these springs would be observed to elongate or contract in such a way as to provide a counteracting force to balance the inertial force. To describe such force as "fictitious" is therefore somewhat misleading. One would like to have some convenient label that distinguishes inertial forces from forces that arise from true physical interactions, and the term "psuedo-force" is often used. Even this, however, does not do justice to such forces experienced by someone who is actually in the accelerating frame of reference. Probably the original, strictly technical name, "inertial force," which is free of any questionable overtones, remains the best description.
From The Variational Principles of Mechanics - 4th Ed., Cornelius Lanczos, Dover Pub., page 98.
Whenever the motion of the reference system generates a force which has to be added to the relative force of inertia I’, measured in that system, we call that force an “apparent force.” The name is well chosen, inasmuch as that force does not exist in the absolute system. The name is misleading, however, if it is interpreted as a force which is not as “real” as any given physical force. In the moving reference system the apparent force is a perfectly real force, which is not distinguishable in its nature from any other impressed force. Let us suppose that the observer is not aware of the fact that his reference system is in accelerated motion. Then purely mechanical observations cannot reveal to him that fact.
From Cosmological Physics, John A. Peacock, Cambridge University Press, (1999), page 6-7
The 'weak equivalence principle' is a statement only about space and time. It says that in any gravitational field, however strong, a freely falling observer will experience no gravitational effects - with the important exception of tidal force in non-uniform fields. [...] It may seem that we have actually returned to something like the Newtonian viewpoint: gravitation is merely an artifact of looking at things from the 'wrong' point of view. This is really not so; rather, the important aspects of gravitation are not so much first order effects as second order tidal forces: They cannot be transformed away and are the true signature of gravitating mass. However, it is certainly true in one sense to say that gravity is not a 'real' force, the gravitational acceleration is not derived from a 4-force and transforms differently.
.. Maybe i am not getting the idea of what a pseudo force is...
Does this help?

Pete

mgb_phys
Homework Helper
I sometimes find it helpful to think first about the inertial force we've all experienced in an accelerating vehicle. We're certainly pushed back into the seat (or thrown forward under deceleration), so the force feels "real" enough. What is missing, however, is any kind of field that exerts this force, much less a source for such a field. This distinguishes such forces from ones like electrical or magnetic forces (or gravitational forces, at least when understood as Newton did), where there are fields with sources.

The Equivalence Principle definitely makes the question more interesting, and I can't say that I've ever really felt I had a complete handle on it. I'm incapable of riding a subway without wondering how the forces I feel as I get jerked around are somehow equivalent to gravitational forces.

rbj
What is a centrifugal force? Is it a pseudo force?

Does it really exist?.. Maybe i am not getting the idea of what a pseudo force is...
it's a pseudoforce that appears in an accelerated frame of reference that, within that frame of reference of curved or circular motion, appears to pull objects away from the center of rotation.

the real force is the centripetal force that is pushing the objects in circular motion toward the center of rotation. so, if you're in a car going around a bend in the road, it's not that you're being pulled outward and pressing against the car door (despite what you think you feel) but that the car door is pushing you in the direction you are being accelerated (which, in circular motion, is toward the center of rotation).

rcgldr
Homework Helper
Centripetal force is the force that accelerates a moving body "inwards", and centrifual force is the equal and opposite reaction force to the acceleration caused by the centripital force.