Newton Third Law of Motion

Newton’s Third Law of Motion: When a body exerts a force on another body, the other body also exerts a force on the first. We say that two bodies interact with each other.

Newton’s Third law: “In any interaction between two bodies, the force applied by the first body on the second is equal and opposite to the force applied by the second body on the first.” This means force occurs in pairs.

These two forces have equal magnitude and opposite directions. Such a pair of forces exerted by two bodies on each other is called an action – reaction pair. These action – reaction pair act on two different bodies.

When a boy carries a heavy load on his head, the load pushes down on his head. The boy’s head pushes the load upwards. These forces are equal in magnitude.

If you hit a wall with your fist, the wall also hits your fist with the same force, which you feel.

Examples of Newton’s Third Law

1. Cricket player catching a ball: The player has to exert force on the ball to stop it. By Newton’s third law, the ball exerts a force of equal magnitude on the hand. If he pulls his hand back, smaller force will be exerted. If the keeps his hand still, larger force will be exerted.

2. Walking of a person: A person is able to walk because of the Newton’s third law of motion. During walking, a person pushes the ground in backward direction and in the reaction; the ground also pushes the person with equal magnitude of force in opposite direction. This enables him to move forwards direction against the push.

3. Recoil of gun: When bullet is fired from a gun, then the bullet also pushes the gun in opposite direction with equal magnitude of force. This results gunman feeling a backward push i.e. recoil force from the gun. Since the gun has greater mass than bullet, acceleration of the gun is much less than the acceleration of the bullet.

4. Rocket Propulsion: The propulsion of the rocket is based on the principle of action and reaction. The rapid burning of fuel produces hot gases which rush out from the nozzle at the rear end at a very high speed. The equal and opposite reaction force moves the rocket upward at a greater speed.

5. When you jump out of the boat onto the shore, you pushes the boat backwards with your feet. By Newton’s third law, the boat pushes you in the forward direction. Thus, you move towards the shore and the boat moves away from the shore.

Sample Questions

(More Questions for each concept available in Login)

Question : 1

When a person carries a heavy load on their head, which statement accurately describes the forces involved according to Newton’s Third Law of Motion?
A. The load exerts a force on the person's head, but the person's head does not exert any force on the load.
B. The load exerts a downward force on the person's head, and the person's head exerts an upward force on the load.
C. The person exerts a force on the load, and the load exerts a force on the person's shoulders.
D. The person's head exerts a force on the load, but the load does not exert any force on the person's head.
Right Option : C
View Explanation

Question : 2

A rocket is launched into space using _________________
A. first law of motion		B. second law of motion
C. third law of motion		D. law of conservation of energy
Right Option : C
View Explanation

Question : 3

A rocket can go vertically upwards in earth's atmosphere because _______________---
A. it is lighter than air
B. of gravitational pull of the sun
C. it has a fan which displaces more air per unit time than the weight of the rocket
D. of the force exerted on the rocket by gases ejected by it
Right Option : D
View Explanation