Question

Push against a wall. How much work did you do in pushing against the wall?

Even if you push hard all day against a wall, it will not move at all. So, since the distance travelled is zero, the work performed will also be zero.

Outwardly, nothing seems to change. Yet you feel tired. It is because when you constantly push hard against the wall, your muscles get tired as they stretch and contract i.e., they change in shape. The heart pumps more blood to these muscles. Complex chemical reactions take place in your body which make you feel tired, thereby performing work within your system, but the work done on the wall is still zero.

Answer 1

The work done on the wall is zero because the wall does not move, so its displacement is zero.

W = F × d

Since d = 0,

W = 0

Although you feel tired, this is due to internal work done by the muscles and chemical reactions in the body. No mechanical work is done on the wall.