The Concept of Potential Energy

It is the energy possessed by a body by virtue of the position in a field of force or by its configuration.

A few examples from our daily life of the bodies possessing potential energy are given below
1. The potential energy of water in dams is used to run turbines in order to produce electric energy from the generators.
2. The potential energy of the wound spring of a clock is used to drive the hands of the clock.
3. Due to the potential energy of the compressed spring in a loaded gun, the bullet is released with a large velocity on firing the gun.
4. Due to the potential energy of the stretched bow, the arrow goes forward with a large velocity on releasing the bow.
The first example pertains to the gravitational potential energy possessed by a body due to its location (position) above the surface of earth, while the other three are the examples of the potential energy possessed by a body by virtue of its configuration.

Gravitational potential energy

Consider that a body of mass M is lying at point A on the surface of earth. If g is acceleration due to gravity on the surface of earth, it will be attracted towards the centre of the earth with a force M g, equal to the weight of the body.

In order to move the body up from point A to B with zero acceleration, a force equal to M g has to be applied on the body in upward direction. If the body is moved through a height h, then work done
W = force distance = M g h
This work done is stored inside the body as its gravitational potential energy at point B.
Therefore, potential energy = M g h

In fact, M g h will be equal to change in gravitational potential energy, which is usually called the change in potential energy of the body in going from point A to B. However, M g h will represent potential energy of the body at point B, if its potential energy at the surface of earth is taken as zero level of potential energy.