If a point in a rigid body is not fixed, it can possess rotational motion as well as translational motion. The general motion of a rigid body consists of both these motions. For example, the motion of an automobile wheel on a plane horizontal surface.

The kinetic energy of translation is

(KE)tr = ½Mvcm2

The kinetic energy of rotation is

(KE)rot = ½Iω2

The total energy of the body due to translation and rotation is the sum of these two kinetic energies.