Question

State Newton's third law of motion and illustrate it with three examples.

Answer 1

Newton's third law states that to every action there is an equal and opposite reaction.

Example 1:

Process of walking:

1. While walking, a man presses the earth backward with his foot. The earth gives a reaction to the man in the forward direction.
2. Action acts on the earth, while reaction acts on man.
3. These two are equal and opposite. Since man is much lighter than the earth, an observable motion takes place in man.

Example 2:

Rebounding of the rubber ball:

1. Consider a rubber ball striking a rigid wall. The ball exerts an action on the wall.
2. Since the wall is rigid, the ball is brought to rest immediately. The rate of change of momentum of the ball and hence the force on the ball (reactions from the wall) is large.
3. Due to this reaction, the ball rebounds back.

Example 3:

Recoil of a gun:

1. Before firing the bullet is at rest inside the gun. On firing, the bullet acquires a velocity in a very small interval of time.
2. Thus, the rate of change of momentum of the bullet, which is equal to the force on the bullet, is very large. This is the action on the bullet.
3. An equal reaction is experienced by the gun in opposite direction, due to which it acquires some momentum and gets a recoil.