Potential Energy (PE):

It is the capacity of a body to do work by virtue of the position of the body, with respect to given datum level. A body of weight W Newton & at height (Z) above the datum level has potential energy (W × Z) whereas the body of weight W₂ and placed at level - H₂ below the datum level has potential energy ( - W₂  H ₂ ) , with respect to the datum level.

Potential energy of a spring similarly can be illustrated to be equal to (½) k s ²  where 's'

is the displacement of the spring by the undeformed position.

A prismatic bar of area of cross-section A, length L and elastic constant E, when stretched or deformed, the work of elastic force may be calculated by treating it as a spring of stiffness k,

                                                                        k = A E/ L

It is the capacity of doing work by virtue of the motion possessed by the body. The motion of a body may be a motion of pure translation or pure rotation or a combination of both translation and rotation. Accordingly, the body shall possess Kinetic-Energy of translation, rotation or both.