The energy produced by mechanical means is called mechanical energy. It has two forms:
(i) Kinetic energy
(ii) Potential energy.
Kinetic energy
The energy possessed by a body by virtue of its motion is called its kinetic energy. A moving object can do work. The amount of work that a moving object can do before coming to rest is equal to its kinetic energy.
Examples of kinetic energy:
(i) A bullet fired from a gun can pierce a target due to its kinetic energy.
(ii) The kinetic energy of a fast stream of water is used to run water mills.
(iii) A moving hammer drives a nail into the wood. Being in motion, it has kinetic energy or ability to do work.
(iv) The kinetic energy of air is used to run windmills.
(v) A fast moving stone can break a window pane. The stone has kinetic energy due to its motion and so it can do work.
Potential energy:
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:
(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.