Potential energy is the energy stored in a body or a system by virtue of its position in a field of force or by its configuration. Potential energy is also called mutual energy or energy of configuration.
It is measured by the amount of work that a body or system can do in passing from its present position or configuration to some standard position or configuration, called zero position or zero configuration.
Examples of potential energy due to position:
(i) A body lying on the roof of a building has some potential energy. When allowed to fall down, it can do work.
(ii) The potential energy of water stored to great heights in dams is used to run turbines for generating hydroelectricity.
Examples of potential energy due to configuration:
(i) In a toy car, the wound spring has potential energy. As the spring is released, its potential energy changes into kinetic energy which moves the toy car.
(ii) Astretched bow possesses potential energy. As soon as it is released, it shoots the arrow in the forward direction with a large velocity. The potential energy of the stretched bow gets converted into the kinetic energy.
(iii) Due to the potential energy of the compressed spring in a loaded gun, the bullet is fired with a large velocity on firing the gun.
Different types of potential energies.
Three common types of potential energies are as follows:
(i) Gravitational potential energy:
It is the potential energy associated with the state of separation of two bodies, which attract one another through the gravitational force.
(ii) Elastic potential energy:
It is the potential energy associated with the state of compression or extension of an elastic (spring like) object.
(iii) Electrostatic potential energy:
The energy due to the interaction between two electric charges is electrostatic potential energy.
Gravitational Potential Energy
Gravitational potential energy. The gravitational potential energy of a body is the energy possessed by the body by virtue of its position above the surface of the earth.
Expression for G.P.E.
Consider a body of mass m lying on the surface of the earth, as shown in Fig. 6.15. Let ‘g’ be the acceleration due to gravity at this place
For heights much smaller than the radius of the earth (h << RE) the value g can be taken constant.
Force needed to lift the body up with zero acceleration,
F = Weight of the body = mg
Work done on the body in raising it through height h,
W = F . h = mg . h
This work done against gravity is stored as the gravitational potential energy (U) of the body.
∴ U = mg h
At the surface of the earth, h= 0
∴ Gravitational P.E. at the earth’s surface = zero.