Whenever a force acts on a body and the body moves, work is done. The unit is the N.m which is called the Joule. Energy Energy is the ability to do work.
Kinetic energy is energy due to motion.
This is called gravitational potential energy . When a body of mass m is moved a distance h against gravity, the increase in its potential energy is equal to mgh. Elastic potential energy is associated with a stretched spring. If no external forces act of a system, the sum of the kinetic, gravitational, and elastic energy is conserved. The rate of doing work is called power.