When a force acts on a body, then it is called the action. The force produced as a result of action acts on another object but in opposite direction is called reaction. Newton formulated a law in relation to action and reaction, which is called Newton’s third law of motion.According to this law, for every action, there is an equal and opposite reaction. Action and reaction always operate on different objects but in opposite directions.
(1) Action and reaction act on two different objects.
Experiment: Take an oil funnel and fill half of it with water and fix it on a small boat, as shown in the figure. The funnel is heated at the bottom with the help of a lamp. When steam begins to come out from the jet fastly, the boat experiences a force in a backward direction, and it begins to move in a direction opposite to the direction of the outgoing steam the body. It can also be stated as: The rate of change of momentum is equal to the force applied to the body and the change in momentum always takes place in the direction of the force. From this experiment, it is clear that the force (action) due to the outgoing steam acts in a forward direction and force of reactions acts, i.e., moving boats in the opposite direction. This proves that action and reaction act on two different objects.
(2) Experiment: Take two similar spring balances, as shown in the figure. Fix one spring balance to a rigid support and then fix the hook of another spring balance in its hook, and stretch (pull) the whole system gently. Observe the readings of both the spring balances. We see that the reading of both the spring balances is exactly equal. If one balance reads 5 kg, the other also read 5 kg. Obviously, the tension of the first on the second spring balance is exactly equal the tension of the second on the first spring balance. This means that the action and reaction forces are equal and opposite.
