91Ó°ÊÓ

A rigid body has its mass concentrated at the center of mass (CM). There is no distribution of mass along any of the axes.The rotational inertia of a rigid body becomes zero. The body does not possess any angular momentum. Thus, there will be no importance of rotational motion for this body of concentrated mass.

A rigid object having concentrated mass has zero rotational inertia. Thus, the torque acting on it becomes zero.

Thus, the mass of a rigid object concentrated at the center of mass would not be considered for the rotational motion.

For the rotational motion, the object mass must be distributed along the axes. So, it has rotational inertia about the axes and the torques acting on the distributed mass object.

Thus, the analysis of a distributed mass object would be considered for the rotational motion.