If force is applied to a body and it begins to move and goes to some distance, it is said ‘work is done’. When we use force to move things, we do work.
We estimate the amount of work done by a moving body by measuring the distance covered by it due to the force applied. Pushing a chair is easy but pushing a cupboard full of books is difficult. We have to use more force to move the cupboard. So we do more work in moving the cupboard than in moving the chair.
So, if the body does not move at all inspite of applying the force, we say ‘no work is done’. Thus without displacement of the body. No work is done. Work is done only when a body moves over some distance.
When a labourer drives a trolley work is done. When bullocks pull a plough in the field, they do the work. When a steam or electric engine runs a train, the engine does the work. When we press a switch and an electric fan begins to move, the work is done by the motor fitted in the fan. When birds fly in the sky, they do the work.
Thus when a body is displaced by a force, work is said to be done.