# Thread: GR and centrifugal force

1. Member
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I don't know a lot about GR, but as I understand it an observer in a rotating frame is free to consider himself to be at rest. If this is the case then does this not mean that the centrifugal or inertial force that he experiences is a real force and not a pseudo force? In addition it would seem that this would be true even though the centrifugal force would not have a source. Is this correct?

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On 2002-04-29 18:33, Ring wrote:
I don't know a lot about GR, but as I understand it an observer in a rotating frame is free to consider himself to be at rest. If this is the case then does this not mean that the centrifugal or inertial force that he experiences is a real force and not a pseudo force? In addition it would seem that this would be true even though the centrifugal force would not have a source. Is this correct?
Sorry, is not correct. An inertial frame has a constant velocity (and therefore no acceleration). Anytime you experience any sort of force, you are not in an inertial frame because you are being accelerated by that force.

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There is no such thing as an *inertial force*. Inertia is a lack of a force. The term *centrifugal force* is an often-used misnomer, because it is really inertia which is not a real force. However, I have already stated this too many times in another place here in this forum and will not bother with arguing the point ad infinitum.

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I have searching for info on this and ran across this quote at another forum.

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

Albert Einstein

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"Centrifugal force results when describing motion relative to a non-inertial, rotating reference frame. Relative to such frame it most certainly exists, statements by ignorant school teachers notwithstanding."

Person quoting Matti Meron

Yep. This comes up all the time and should be in the FAQ. Since Einstein's
principle of equivalence, centrifugal force is an entirely legitimate force. In the Newtonian view, OTOH, it is thought of as an artifact arising from a "non-inertial" frame. However, inertial frames are usually defined
as those in which Newton's laws apply. The only way out of this circular argument is to posit "Absolute Space", which Newton did.

Matti Meron's response.

Dr Meron is a Ph.D. physicist from the University of Chicago.

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