Work is done whenever the given two conditions are satisfied:
- A force acts on the body.
- There is a displacement of the body by applying force in or opposite to the direction of the force.
When a person holds a bundle of hay over his head, there is no displacement in the hay bundle. Although the force of gravity is acting on the bundle, the person is not applying any force on it. Hence, in the absence of force, work done by the person on the bundle is zero. His head gets tired as he experiences muscular fatigue. This fatigue is due to the conversion of chemical energy into thermal energy by muscular effort. The person has done no work as his effort causes no displacement of the bundle over his head, i.e., S = 0.