1. The energy possessed by a body by virtue of its position or configuration is called its potential . It is measured by the amount of work that the body can do in changing its present position to some other position above the surface of earth or changing its configuration. It can also be measured by the amount of work done by the body to return to the surface of earth from some higher position or to the original configuration from changed configuration.
2. Some examples of potential energy due to position:
a) Water at higher level (stored in reservoirs) has a huge amount of gravitational potential energy due to which it can be drive a water turbine, when allowed to fall down. This is the principle which is used to generate hydroelectricity.
b) A lifted weight possesses a potential energy because the work done to raise the weight is stored in it in the form of potential energy. If a lifted weight is allowed to fall on a nail, fixed vertically on the ground, the nail gets pressed into the ground. But this would have not been the case if the weight was simply placed on the nail. Thus, the energy required for pressing the nail into the ground has been supplied by a special position of weight.
3. Some examples of potential energy due to configuration
a) Consider a body trying to shoot a bird sitting on the branch of a tree with his catapult. For this, he stretches out the string of his catapult up to a maximum length. When the catapult is suddenly released, the pebble kept attached with it springs out with a high speed. If the string has not stretched and the pebble is only released, there will no movement of the pebble: it will simply drop down on the earth due to gravity. So in this case some work has been done by rubber string being transferred from its state of expansion to its state of contraction. In other words, due to change in configuration some amount of energy is stored in the rubber string.
b) When the spring of watch is wound, its various winding come close together. The work done in winding the spring is stored as elastic potential energy due to changed configuration as a result of which the spring acquires capacity for doing work. Thus on unwinding itself, the spring drives the hands of the watch.
c) A stretched bow has elastic potential energy due to change in its configuration. When released, the bow does work in imparting K.E. to the arrow.
4. Broadly speaking, the potential energy is of following three types:
i) Gravitational potential energy
ii) Elastic potential energy
iii) Electrostatic potential energy