The force applied to a body to make it move through a distance is called work. It is the measure of energy transfer that occurs when an object is moved over a distance. Work is done only if an object changes its position due to the force used on it. Work is not done if a body is not moved from its original position, even if force is applied.

Energy is defined as the capacity to do work. It exists in various forms such as potential energy, kinetic energy, thermal energy, nuclear energy and electrical energy. The SI unit of energy is joule J . Examples of two main forms of energy: Kinetic energy: An object possesses this energy by virtue of its motion. Potential energy: An object possesses this energy by virtue of its position and shape.