I need help in understanding why, in accelerated rolling, the center of mass must be at the origin of an inertial frame of reference in order for the second law to be applicable.


  • $\begingroup$ Would be really helpful if you could state the reason for the downvote. $\endgroup$
    – zv.diego
    Apr 28, 2016 at 23:42
  • $\begingroup$ The question is unclear. My best guess of the answer is in that case you can ignore the pseudo force when calculate the moment . $\endgroup$
    – velut luna
    Apr 29, 2016 at 0:11
  • 2
    $\begingroup$ Possible duplicate of Why is the center of mass frame always used in rigid body dynamics? $\endgroup$ Apr 29, 2016 at 3:37
  • $\begingroup$ This question has been answered before in here multiple times. It is hard to find past questions unless you use the right keywords. $\endgroup$ Apr 29, 2016 at 3:38

1 Answer 1


Newtons 2nd law only holds in an inertial frame.

If you use the center of mass of the rolling object as your frame of reference then the frame will be accelerating and F=MA won't hold. However if you fix the frame of reference to a relatively stationary point, say the surface of the earth, it will.

Even in this case the frame is not truly inertial, but the acceleration is so small as to be insignificant.

An example often given is that if you are sitting in a bus and the bus is accelerating objects will appear to slide towards the back of the bus, even though no force is acting on them in that direction. What is actually happening is that the whole bus is accelerating forwards and the objects sliding backwards are actually at rest.


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