Fig. 1-1 A man is pushing a broken car

Pushing a broken car on the road is exhausting in a hot summer day (Fig. 1-1). When you exert a force on the car to move it, work is done and you feel tired on losing energy. In physics, we say that energy is transferred from your body to the car by doing work.

Work is done whenever there is a displacement in the direction of a force. It can be defined as

or

The unit of work is therefore Newton-metre (), which is also called Joule (J). Work is a scalar quantity; it has magnitude but no direction. It is important to note that displacement is always involved in the process of doing work, and that work is done only when there is a displacement in the direction of the force. The following examples serve to illustrate these principles.