After reading (https://en.wikipedia.org/wiki/Reactive_centrifugal_force) (especially third paragraph of the introduction) and comparing it with the answer by Bob Jacobsen posted here (Why does a rotating non-rigid object elongate?), I cannot make the statements agree with each other. My question is:

Are the centripetal force and the reactive centrifugal force also present in the rotating frame? I would guess so as the rotating object needs to be hold in place (applies to any frame). But additionally, there is now this "fictitious" centrifugal force, which causes the elongation of non-rigid objects, right?


Centrifugal force is a pseudo-force that only exists in the non-inertial (rotating) frame. For example when your car takes a sharp turn, you feel an outwards force although it seems like nothing is causing it. It is added to explain the apparent outwards force and make sure that Newton's laws remain valid. The centripetal force exists in both reference frames as it is a 'true force' and is the reason why the object is rotating. However to you inside the car, you will only experience the centrifugal force.

  • $\begingroup$ Thanks, wouldn’t that mean the wikipedia article is wrong, at least the third paragraph of the introduction? $\endgroup$ – ExOrbitant Feb 9 '20 at 11:00
  • $\begingroup$ The mentioned wikipedia article is correct. I have changed the wording a bit. Is it clearer now? $\endgroup$ – Sam Feb 9 '20 at 11:17
  • $\begingroup$ I cannot see the changes you made. Could it because the changes haven‘t yet been validated by other wikipedia authors? I am not sure...still, this third paragraph in the introduction causes me headache. It says that the fictitious centrifugal force only exists in the rotating frame in addition to the reactive force, which can be assumed to be the reactive centrifugal force that counteracts the centripetal force. So if the the latter only exists in the inertial frame, so must the reactive centrifugal force only exist in the inertial frame. „in addition“ makes no sense to me... $\endgroup$ – ExOrbitant Feb 9 '20 at 12:14
  • $\begingroup$ No, I meant that I changed the wording of my answer. The wikipedia paragraph was correct in itself. The centrifugal force counteracts the centripetal force only in the rotating frame. Hence the body is at rest in the rotating frame. In the inertial frame, only centripetal force exists and hence the body is in rotational motion. $\endgroup$ – Sam Feb 9 '20 at 14:28
  • $\begingroup$ Thanks Sam, but it is still not clear, unfortunately. What is about the „reactive“ centrifugal force? If the „fictitious“ centrifugal force were to counteract the centripetal force and there were no „reactive“ centrifugal force, then the sum of forces in radial direction would be 0. The wikipedia article says that all three forces are present in rotating frame, at least I understand it that way. Am I understanding something wrong? $\endgroup$ – ExOrbitant Feb 9 '20 at 15:04

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