Newton Third Law of Motion The Action and Reaction Pair - Detailed Guide

Newton Third Law of Motion The Action and Reaction Pair - Detailed Guide

Vishal kumarUpdated on 02 Jul 2025, 05:07 PM IST

Newton's Third Law of Motion states that any given force in one direction will always return in equal measure and opposite in direction to the body that applied it. This principle explains that force always works in pairs-in other words, every interaction between two objects always generates two forces that are equal in size but reverse in direction. These action and reaction forces coexist at the same point in time but are different bodies and therefore, cause equilibrium for an entire system.

Newton Third Law of Motion The Action and Reaction Pair - Detailed Guide
Newton Third Law of Motion The Action and Reaction Pair

Newton’s Third Law of Motion

Newton’s third law of motion is defined as the law of action and reaction. The law of action and reaction states that, for every action, there will be an equal and opposite reaction.

In this universe, when any force is applied to an object, that object will exert an equal amount of force but in the opposite direction to that applied force. A force is nothing but an action of pull or push that acts on an object by which it causes an interaction with another object.

The force between objects can be classified as

  • Contact force
  • Action at a distance

Contact force happens when the two objects are having physical contact with each other. Examples of contact force are frictional force, air resistance, and tensional force.

Action at a distance force happens when the two objects do not have any physical contact with each other. Examples of action at a distance force are gravitational force, electrical force and magnetic force. When we jump on the ground even though our foot doesn’t touch the ground some gravitational force will appear on our feet by moving back to the ground.

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Action And Reaction Pair in Newton’s 3rd Law

According to Newton’s third law, there will be an equal and opposite reaction for any action. Consider that object A and object B interact with each other, by Newton’s third law these objects will exert force on one another.

This can be given with a mathematical expression as

Fa= - Fb

Here when object A exerts a force on another object B, then an equal amount of force will be exerted back on object A but in the opposite direction which is denoted with a minus (-) symbol.

Now we can illustrate the Action and reaction pair with an example.

  • When we sit on a chair, we exert a downward force on the chair which is action. Similarly, the chair will exert an upward force on you which is a reaction. These two forces are action and reaction pairs. So a pair of forces acts on objects which are interacting with each other.
  • When a fish swims in water it exerts a downward force on the water – action. Since the force occurs in mutual interaction the water will exert an equal amount of force on the fish but in the opposite direction i.e. upwards – reaction.
  • Consider a bird flying in the sky. The bird swings the wing in a downward direction to push the air downwards - action. Since the force occurs in mutual interaction the air will exert an equal amount of force on the wing but in the opposite direction i.e. upwards- reaction.

Examples of Newton's Third Law of Motion

The third law of motion examples in daily life is given below.

  • Gun mechanism
  • Bouncing a ball
  • Walking on ground
  • Using of hammer for hammering
  • Balloon air is evacuating
  • Rowing a boat
  • Moving of car
  • Sports like hockey
  • Using an elastic band
  • Slingshot

Frequently Asked Questions (FAQs)

Q: Why do you feel a force on your hand when catching a ball?
A:
When catching a ball, you feel a force on your hand due to Newton's Third Law. As your hand exerts a force
Q: How does Newton's Third Law explain the concept of rocket propulsion in water?
A:
Rocket propulsion in water, like in a jet ski or torpedo, follows Newton's Third Law. As water is forcefully expelled backward (action), it exerts an equal and opposite force on the vehicle (reaction), propelling it forward through the water.
Q: Why do you feel a force on your hand when you hit a wall?
A:
When you hit a wall, you feel a force on your hand due to Newton's Third Law. As your hand exerts a force on the wall (action), the wall exerts an equal and opposite force back on your hand (reaction). This reaction force is what you feel as the impact.
Q: Why do you feel a force pushing you back into your seat when a car accelerates?
A:
The force pushing you back into your seat during acceleration is due to Newton's Third Law. As the car seat pushes you forward (action), your body pushes back on the seat with an equal force (reaction). This backward force is what you feel pushing you into the seat.
Q: Can you explain how Newton's Third Law applies to the recoil of a cannon?
A:
The recoil of a cannon is a classic example of Newton's Third Law. When the cannon fires a projectile forward (action), the projectile exerts an equal force back on the cannon (reaction). This backward force causes the cannon to recoil or move backward.
Q: How does Newton's Third Law explain the concept of thrust in swimming?
A:
Thrust in swimming is a direct application of Newton's Third Law. As swimmers push water backward with their arms and legs (action), the water pushes them forward with an equal force (reaction). This reaction force is what propels swimmers through the water.
Q: How does Newton's Third Law explain the phenomenon of jet propulsion?
A:
Jet propulsion works on the principle of Newton's Third Law. The jet engine expels hot gases backward at high speeds (action). In response, the gases exert an equal and opposite force on the aircraft (reaction), propelling it forward.
Q: How does Newton's Third Law explain the flight of birds?
A:
Birds fly by pushing air downward and backward with their wings (action). According to Newton's Third Law, the air pushes back on the bird with an equal force upward and forward (reaction), generating lift and propulsion for flight.
Q: Why do you feel a force on your feet when standing still?
A:
When standing still, you feel a force on your feet due to Newton's Third Law. Your weight pushes down on the ground (action), and the ground pushes back up on your feet with an equal force (reaction). This upward reaction force is what you feel supporting you.
Q: How does Newton's Third Law explain the concept of rocket staging?
A:
Rocket staging utilizes Newton's Third Law for efficiency. As each stage burns out, it's discarded, reducing the rocket's mass. The remaining fuel then pushes against a lighter rocket, providing greater acceleration. Each stage's ejection is also based on action-reaction pairs.