Fig. 2-1 A car badly damaged in an ancient.

Forces are found everywhere. When we give a push to open a door, or lift up a heavy object, we are exerting forces. There are different kinds of forces; it can be the gravitational force which keeps the Moon moving around the Earth, or the electric force which attracts carbon particles in the toner to deposit in a photocopier. No matter the nature and context in which a force arises, we can never see the force directly, what we see are the effects of the force - a car badly damaged in an ancient (Fig. 2-1), or a race car accelerated by its powerful engine. Forces can break up things, change their shape, or alter their movement. Whenever two or more bodies interact with each other, force is involved. Force has both magnitude and direction and is therefore a vector. The unit of force is Newton (N).