Newton's Third law of Motion

It is a common observation that when we sit on a chair, our body exerts a downward force on the chair and the chair exerts an upward force on our body. There are two forces resulting from this interaction: a force on the chair and a force on our body. These two forces are called action and reaction forces. Newton's third law explains the relation between these action forces. It states that for every action, there is an equal and opposite reaction.

(i.e.) whenever one body exerts a certain force on a second body, the second body exerts an equal and opposite force on the first. Newton's third law is sometimes called as the law of action and reaction.

The effect of third law of motion can be observed in many activities in our everyday life.

The examples are

• When a bullet is fired from a gun with a certain force (action), there is an equal and opposite force exerted on the gun in the backward direction (reaction).
• When a man jumps from a boat to the shore, the boat moves away from him. The force he exerts on the boat (action) is responsible for its motion and his motion to the shore is due to the force of reaction exerted by the boat on him.
• The swimmer pushes the water in the backward direction with a certain force (action) and the water pushes the swimmer in the forward direction with an equal and opposite force (reaction).
• We will not be able to walk if there were no reaction orce. In order to walk, we push our foot against the ground. The Earth in turn exerts an equal and opposite force. This force is inclined to the surface of the Earth. The vertical component of this force balances our weight and the horizontal component enables us to walk forward.