Consider a rigid body rotating about a fixed axis AB. Consider a particle 'p' of mass 'm' rotating in a circle of radius 'r'.
The total torque on all the forces acting on all the particles of the body is:
where , called the moment of inertial of the body about the axis of rotation. Let us note the similarity between
'm' is the mass of the body and does not depend on the choice of the origin or the axes of rotation or the kind of motion. But, the moment of inertia depends on the choice of axis.
However, both the mass and moment of inertia show the resistance offered by the body to translatory motion and rotary motion, respectively.
