Newtons third law of motion-[Action,Reaction,Formula,Equation,Examples]

By the end of this article, you should be able to describe what is Newton's third law of motion- Definition, Formula, Equation, action-reaction pair forces and Examples of newtons 3rd law. Let's start discussing one by one.

Newton's laws of motion. Sir Isaac Newton (1642-1727) made a systematic study of motion and extended the ideas of Galileo. He arrived at three laws of motion which are called Newton's laws of motion.

What is Newtons Third Law - Definition

According to Newton's 3rd law of motion,
To every action, there is an equal and opposite reaction. Let us explain an activity to understand the law.

1. Take a balloon and tie its mouth to a small piece of plastic tube with a narrow bore. Now inflate the balloon and close the opening of the tube with your finger. Remove the finger and let the air escape. The balloon will move in a direction opposite to the direction in which the air escapes.
2. If we fix the inflated balloon on the top of a toy car. We observe that the car is moving in a direction opposite to the direction in which the air escapes. The car moves due to the reaction force exerted by the air on the balloon.

This proves Newton's third law of motion

Must Read: Newtons First Law.

Newton's Third Law Formula - (Newton's Third Law Equation)

Forces in nature always occur between pairs of bodies. Force on body A by body B is equal and opposite to the force on the body B by A.

If F_BA is the force exerted by body A on B
and F_AB is the force exerted by B on A, Then according to Newton's 3rd law,
F_BA= - F_AB
Force on A by B = – Force on B by A.

Book kept on a table. Consider a book of weight W resting on a table top. The book exerts a downward force (action) on the table equal to its own weight W.  According to Newton's 3rd law, the table also exerts an equal and upward force R (reaction) on the book such that
R = - W
As the book is under the action of two equal and opposite forces, it remains in equilibrium.

Jetplanes and Rockets -  In a jet plane or in a rocket, the products of combustion in the form of smoke are ejected outward with a great speed. These gases under pressure apply a reaction force on the rocket and the jet plane in the opposite direction. This reaction force pushes the jet plane and rocket forward.

Lawn Sprinklers - In a lawn sprinkler when water comes out of the curved nozzles. The sprinkler experiences a backward force and starts rotating sprinkling water in all directions.

Action Reaction Pairs (Action-Reaction Forces)

The above statement shows that a single force can never exist.
The forces always exist in pairs. The two forces act simultaneously. Anyone of them may be called the action and the other reaction. No cause-effect relationship exists between action and reaction.

Important Conclusions of Action-Reaction Pairs ( Action-Reaction Forces)

1. Newton's 3rd law of motion is applicable irrespective of the nature of the forces. The forces of action and reactions may be mechanical, gravitational, electric or of any other nature.
2. Action and reaction always act on different bodies. If they acted on the same body, the resultant force would be zero and there could never be accelerated motion.
3. The forces of action and reaction cannot cancel each other. This is because of action and reaction, though equal and opposite, always act on different bodies and so cannot balance each other.
4. No action can occur in the absence of a reaction. For example, in a tug-of-war, one team can pull the rope only if the other team is pulling the other end of the rope. No force can be exerted if the other end is free. One team exerts the force of action and the other team provides the force of reaction.

Newtons Third Law Examples

• It is difficult to walk on a slippery ground or sand because we are unable to push such a ground sufficiently hard. As a result, the force of reaction is not sufficient to help us move forward.
• It is difficult to drive a nail into a wooden block without supporting it. When we hit the nail with a hammer, the nail and unsupported block together move forward as a single system. There is no reaction. When the block is rested against a support, the reaction of the support holds the block in position and the nail is driven into the wooden block.
• While swimming, a person pushes water with his hands in the backward direction (action) and water, in turn, pushes him forward due to the force of reaction.

This is all about the basics - What is Newton's third law of motion- Definition, Formula, Equation, action-reaction pair forces and Examples of newtons 3rd law.