We know that rigid body will keep rotating without external force. This answer explains
Rotational inertia differs from ordinary “linear” inertia in that it is a derived principle: it can be derived mathematically from Newton’s laws of motion, so in that sense it has (in my opinion) a slightly less fundamental status among the laws of physics. Rigid bodies don’t “want” to keep rotating in the same fundamental sense that particles “want” to keep moving in a straight line with a fixed velocity - they do end up rotating but it’s because of a process we understand well and can analyze mathematically
Can someone present the mathematical derivation referred above, I am not able to find this anywhere? For me individual mass particles in the body seems to be violating newton's first law as they are changing velocity direction without any force being applied.
