Energy can be defined as the capacity or ability of the body to do work. Work is always done at the expense of energy. In other words, energy is spent when a force does work on an object. The SI unit of energy is Joule and in cgs system erg. Energy is of two forms: (a) Kinetic energy (b) Potential energy.
(a) Kinetic energy: Kinetic energy is defined as 'energy of motion, the energy expended as a result of action'. It is the energy 'Possessed by a body by virtue of its motion'. It is the energy resulting from the action of force over a given distance.
Example:
(i) A bullet fired from a gun.
(ii) A rolling ball have kinetic energy.
(iii) 100 m run body moves from one point to another due to kinetic energy.
(iv) Volley ball spiking.
(v) Blocking in volleyball.
(vi) Lay up shot in basketball.
(vii) Jump shot long and high in handball.
(viii) Vertical jump etc.
Kinetic energy of a body is measured by the amount of work done by it before it comes to rest from its present state of motion.
Kinetic energy = MV2
Where,
M = The mass of the body
V = The velocity at which it is moving
(b) Potential energy: It is energy which is stored up in a body by reasons of the position of the body, it represent the possibility of doing work. In other words, it is the energy possessed by a body by virtue of its state or position is called potential energy.
Example: A person who jumps into the air has expended kinetic energy when he reaches the highest point of jump he possess purely, potential energy in proportion to his height from his base. Potential energy - mgh
(i) Toss of ball before service in tennis.
(ii) Handstand on parallel bar.
(iii) Stretching the elastic belt.
(iv) Bow stretch in Archery.
