Work is said to be done when a force acts on a body and moves it in the direction of the force. Greater is the force acting on a body and the the the longer is the distance moved by it, the the the larger would be the work done. Mathematically, Work is a product of force F and displacement S in the direction of the force. Thus

Work done = Force x displacement

Or             W = F S .........(i)

If the force is unbalanced, it causes acceleration. This involves doing work to move it in a certain direction.