The motion of an object under the action of a force, which is always directed towards or away from a fixed point, is called central force motion. Gravitational force is one such example. Consider the motion of an object P of mass m with respect to a fixed point O, called inertial reference. Let $\overline{R}$ be the position vector, $\overline{v}$the instantaneous velocity vector and $\hat{e}$ , the radial direction.