I had quite a few posts about this some weeks ago, but I am still not sure about it. My question is about why you can always view the motion of an object as a traslation of the cm and a rotation around it. It makes sense in the light of the cm being the point which moves as a point particle only subject to external forces. But then that must mean that what causes the rotational part of the motion is purely internal forces. Is it then so that the sum of all the internal forces causing the rotation is zero with respect to an inertial frame of reference? Hope it made at least somewhat sense..