Newton’s third law of motion

The third law of motion states that when one object exerts a force on another object, the second object instantaneously exerts a force back on the first. These two forces are always equal in magnitude but opposite in direction . The two opposing forces are also known as action and reaction forces.

Some examples to illustrate Newton’s third law of motion:-

When a force is applied through the free end of spring balance A, it is observed that both the spring balances show the same readings on their scales. It means that the force exerted by spring balance A on balance B is equal but opposite in direction to the force exerted by the balance B on balance A. The force which balance A exerts on balance B is called the action and the force of balance B on balance A is called the reaction. This gives us an alternatives statement of the third law of motion i.e., to every action there is an equal and opposite reaction.

Fig :- Action and reaction forces are equal and opposite

When a gun is fired, it exerts a forward force on the bullet. The bullet exerts an equal and opposite reaction force on the gun. This results in the recoil of the gun. Since the gun has a much greater mass than the bullet, the acceleration of the gun is much less than the acceleration of the bullet. The third law of motion can also be illustrated when a sailor jumps out of a rowing boat. As the sailor jumps forward, the force on the boat moves it backwards.

Fig:- A forward force on the bullet and recoil of the gun.

Fig:- As the sailor jumps in forward direction, The boat moves backwards.