Work and Energy
Work is said to be done on a body when non-zero force acting on it displaces it in the direction of the applied force. When the direction of applied force and that of the displacement of the object are the same, the work done on the object is said to be positive. When the direction of the applied force and that of the displacement of the object are opposite to each other, the work done on the object is said to be negative. Work done on a body is said to be zero, if the non-zero force acting on it produces zero displacement.
Energy is the capacity of an object to do work. There are various forms of energy such as heat energy, electrical energy, kinetic energy, potential energy etc. Kinetic energy is the energy possessed by a body by virtue of its motion. Potential energy is the energy possessed by a body by virtue of its position or configuration. When a body is raised to a height against gravity, work is done on it. This work done is stored in the body as its gravitational potential energy. Energy can neither be created nor be destroyed; it can only be converted from one form to another. This is known as law of conservation of energy.
Power is the rate of doing work or the rate of transfer of energy. It measures the speed of work done. A more powerful agent may finish a work in less time than the less powerful agent.