Newton Third Law of Motion The Action and Reaction Pair

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

Edited By Vishal kumar | Updated on Jul 02, 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’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

F_a= - F_b

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.

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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)

1. In this which will not be an example for action-reaction pair 1. Bird flies using wing 2. Movement of fish 3. Car acceleration 4. Movement of air

Movement of air

2. The bird flying in the sky illustrates 1. Constant force 2. Zero force 3. Mutual interaction force 4.No force

Mutual interaction force

The bird swings the wing in 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 opposite direction i.e upwards - reaction.

3. Define Newton’s third law of motion action reaction pair.

Newton’s third law of motion states that, For every action there will be an equal and opposite reaction.

When we sit on a chair, you will 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.

4. What are the forces that act between objects?

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.

5. What is the another term for Newton's third law of motion.

Law of action and reaction.

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

6. How does Newton's Third Law apply to everyday situations?

Newton's Third Law applies to many everyday situations. For example, when you walk, you push backward on the ground with your feet, and the ground pushes forward on you with an equal force, propelling you forward. Similarly, when you jump off a boat, you push the boat backward as you jump forward.

7. Why does a rocket move forward when it expels gases backward?

A rocket moves forward due to Newton's Third Law. As the rocket expels gases backward (action), the gases exert an equal and opposite force on the rocket (reaction), pushing it forward. This principle is known as thrust and is the basis for rocket propulsion.

8. How does Newton's Third Law explain the recoil of a gun?

When a gun fires a bullet, it exerts a forward force on the bullet (action). According to Newton's Third Law, the bullet exerts an equal and opposite force back on the gun (reaction). This backward force causes the gun to recoil or "kick" when fired.

9. Can you provide an example of Newton's Third Law in sports?

In swimming, Newton's Third Law is evident when a swimmer pushes water backward with their arms and legs (action). The water pushes back on the swimmer with an equal force (reaction), propelling them forward through the water.

10. How does Newton's Third Law apply to collisions?

In collisions, Newton's Third Law ensures that the forces between colliding objects are equal and opposite. For example, when two cars collide, the force Car A exerts on Car B is equal and opposite to the force Car B exerts on Car A, regardless of their sizes or speeds.

11. What is Newton's Third Law of Motion?

Newton's Third Law states that for every action, there is an equal and opposite reaction. This means that when one object exerts a force on another object, the second object exerts an equal force back on the first object, but in the opposite direction.

12. Why don't action and reaction forces cancel each other out?

Action and reaction forces don't cancel each other out because they act on different objects. The action force acts on one object, while the reaction force acts on another object. These forces are equal in magnitude but opposite in direction, acting on separate bodies.

13. Can you explain the concept of action-reaction pairs?

Action-reaction pairs are the two forces described in Newton's Third Law. They are equal in magnitude, opposite in direction, and act on different objects. For example, when a book rests on a table, the book exerts a downward force on the table (action), and the table exerts an equal upward force on the book (reaction).

14. How does Newton's Third Law relate to conservation of momentum?

Newton's Third Law is closely related to the conservation of momentum. When two objects interact, the forces they exert on each other are equal and opposite. This leads to changes in momentum that are equal in magnitude but opposite in direction, ensuring that the total momentum of the system remains constant.

15. Why do you feel a "push" when accelerating in an elevator?

When an elevator accelerates upward, you feel a "push" due to Newton's Third Law. The elevator floor pushes up on your feet (action), and your body pushes down on the floor with an equal force (reaction). This additional force, combined with your weight, creates the sensation of being "pushed" down.

16. Can Newton's Third Law be applied to static situations?

Yes, Newton's Third Law applies to static situations as well. For example, when a book is at rest on a table, the book exerts a downward force on the table due to gravity, and the table exerts an equal upward force on the book. These forces are in equilibrium, keeping the book stationary.

17. How does Newton's Third Law explain why it's harder to walk on ice?

Walking on ice is difficult due to Newton's Third Law. When you try to push backward on the ice with your foot (action), the ice provides little friction, resulting in a smaller reaction force. This reduced reaction force makes it harder to propel yourself forward, causing slipping.

18. Why do lightweight objects move more when hit by a heavy object?

When a heavy object hits a lightweight object, both experience the same force due to Newton's Third Law. However, the lightweight object has less mass, so it experiences greater acceleration (from Newton's Second Law, F=ma). This results in the lightweight object moving more noticeably.

19. How does Newton's Third Law apply to magnetic forces?

Magnetic forces also obey Newton's Third Law. When a magnet attracts a piece of iron, the iron exerts an equal and opposite attractive force on the magnet. This is why two magnets will move towards each other when brought close together.

20. Can you explain how Newton's Third Law relates to the concept of normal force?

The normal force is a direct application of Newton's Third Law. When an object rests on a surface, gravity pulls it downward (action). The surface pushes back with an equal and opposite force (reaction), which is the normal force. This prevents the object from sinking into the surface.

21. How does Newton's Third Law explain why it's easier to float in saltwater than in freshwater?

Floating in saltwater is easier due to Newton's Third Law. The denser saltwater exerts a greater upward force (reaction) in response to your weight (action) compared to freshwater. This increased reaction force makes it easier to stay afloat in saltwater.

22. Why do you feel a forward force when a bus suddenly stops?

When a bus suddenly stops, you feel a forward force due to Newton's Third Law and inertia. Your body, continuing to move forward, pushes against the bus (action). The bus pushes back on you with an equal force (reaction), which you perceive as a forward force.

23. How does Newton's Third Law apply to rocket propulsion in space?

In space, rockets rely entirely on Newton's Third Law for propulsion. As the rocket expels gases backward at high speeds (action), the gases exert an equal and opposite force on the rocket (reaction), pushing it forward. This principle works even in the vacuum of space.

24. Can you explain how Newton's Third Law relates to the concept of drag in fluid dynamics?

Drag in fluid dynamics is a manifestation of Newton's Third Law. As an object moves through a fluid, it pushes the fluid particles out of the way (action). The fluid particles push back on the object with an equal force (reaction), which we perceive as drag or resistance to motion.

25. Why do you feel lighter when jumping on a trampoline?

When jumping on a trampoline, you feel lighter at the top of your jump due to Newton's Third Law. As you push down on the trampoline (action), it pushes back up on you (reaction). This upward force partially counteracts gravity, making you feel lighter.

26. Can you explain how Newton's Third Law applies to the flight of a helicopter?

Helicopter flight relies on Newton's Third Law. The rotor blades push air downward (action), and the air pushes back up on the blades with an equal force (reaction). This upward reaction force provides the lift necessary for the helicopter to fly.

27. How does Newton's Third Law explain why it's difficult to push a heavy object on a frictionless surface?

Pushing a heavy object on a frictionless surface is difficult because of Newton's Third Law. When you push the object (action), it pushes back on you with an equal force (reaction). Without friction, there's nothing to counteract this backward force on you, making it hard to move forward.

28. Why do you feel a "kick" when firing a high-powered rifle?

The "kick" felt when firing a high-powered rifle is due to Newton's Third Law. As the rifle exerts a large forward force on the bullet (action), the bullet exerts an equal backward force on the rifle (reaction). This backward force is what you feel as the "kick" or recoil.

29. How does Newton's Third Law explain the phenomenon of lift in aircraft wings?

Lift in aircraft wings is partly explained by Newton's Third Law. As the wing deflects air downward (action), the air pushes back up on the wing with an equal force (reaction). This upward reaction force contributes to the lift that keeps the aircraft in the air.

30. Can you explain how Newton's Third Law applies to the concept of buoyancy?

Buoyancy is a result of Newton's Third Law. When an object is submerged in a fluid, it displaces the fluid. The weight of the displaced fluid (action) results in an upward force on the object (reaction). This upward force is what we call buoyancy.

31. How does Newton's Third Law explain why it's easier to push a shopping cart than to carry groceries?

Pushing a shopping cart is easier than carrying groceries due to Newton's Third Law. When you push the cart, it pushes back on you with an equal force. The wheels allow this force to be redirected horizontally, making it easier to move than lifting and carrying the same weight.

32. Why do you feel a sudden jolt when jumping onto a hard surface?

The jolt felt when jumping onto a hard surface is due to Newton's Third Law. As your feet exert a downward force on the surface (action), the surface exerts an equal upward force on your feet (reaction). This sudden, large reaction force is what you feel as a jolt.

33. How does Newton's Third Law explain the concept of air resistance?

Air resistance is a manifestation of Newton's Third Law. As an object moves through air, it pushes air molecules out of the way (action). The air molecules push back on the object with an equal force (reaction), which we perceive as air resistance or drag.

34. How does Newton's Third Law explain why it's harder to walk in deep snow?

Walking in deep snow is difficult due to Newton's Third Law. When you push down and backward on the snow (action), the snow pushes up and forward on your foot (reaction). However, because snow is soft, it compresses and provides less reaction force, making it harder to move forward.

35. Why do you feel weightless during free fall?

The sensation of weightlessness during free fall is related to Newton's Third Law. In free fall, there's no surface pushing up on you (no reaction force to your weight). The only force acting is gravity, and since everything is falling at the same rate, you feel weightless relative to your surroundings.

36. How does Newton's Third Law explain the concept of rocket staging?

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.

37. Can you explain how Newton's Third Law applies to the concept of pressure in fluids?

Pressure in fluids is a consequence of Newton's Third Law. When a fluid exerts a force on a surface (action), the surface exerts an equal force back on the fluid (reaction). This reciprocal force per unit area is what we define as pressure.

38. How does Newton's Third Law explain why it's easier to float in the Dead Sea?

Floating in the Dead Sea is easier due to Newton's Third Law. The extremely salty water is denser, so it exerts a greater upward force (reaction) in response to your weight (action) compared to regular water. This increased reaction force makes it much easier to float.

39. How does Newton's Third Law explain the concept of momentum exchange in collisions?

Momentum exchange in collisions is governed by Newton's Third Law. When two objects collide, they exert equal and opposite forces on each other. These forces, acting over the same time interval, result in equal but opposite changes in momentum, preserving the total momentum of the system.

40. Can you explain how Newton's Third Law applies to the concept of static friction?

Static friction is an application of Newton's Third Law. When you try to push an object at rest (action), the surface pushes back with an equal force (reaction) up to a certain limit. This reaction force, parallel to the surface, is what we call static friction.

41. How does Newton's Third Law explain why it's harder to stop a moving truck than a car?

Stopping a moving truck is harder than stopping a car due to Newton's Third Law and inertia. The truck's greater mass means it has more inertia. When brakes are applied, the equal and opposite forces between the brakes and the wheels must overcome this larger inertia, requiring more force and distance to stop.

42. How does Newton's Third Law explain the concept of tension in ropes or cables?

Tension in ropes or cables is a result of Newton's Third Law. When a rope is pulled at one end (action), it pulls back with an equal force (reaction). This equal and opposite force pair creates tension throughout the rope, allowing it to transmit force from one end to the other.

43. Can you explain how Newton's Third Law applies to the concept of centripetal force?

Centripetal force is related to Newton's Third Law. In circular motion, the centripetal force pulling an object toward the center (action) is matched by an equal and opposite force pushing outward (reaction), often called the centrifugal force. This reaction force is what you feel pushing you outward in a turning car.

44. How does Newton's Third Law explain why it's easier to pull a heavy object than to push it?

Pulling a heavy object is often easier than pushing due to Newton's Third Law and friction. When pulling, the reaction force from the object helps to keep you upright and moving. When pushing, the reaction force can work against your balance and motion, especially if the object is tall or unstable.

45. Why do you feel a force on your feet when standing still?

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.

46. Can you explain how Newton's Third Law applies to the concept of air pressure?

Air pressure is a manifestation of Newton's Third Law. Air molecules constantly collide with surfaces, exerting tiny forces (action). The surface pushes back with equal force (reaction). The sum of these microscopic force pairs over an area is what we measure as air pressure.

47. How does Newton's Third Law explain why it's harder to jump on a soft surface than a hard one?

Jumping is harder on a soft surface due to Newton's Third Law. When you push down to jump (action), a soft surface compresses and provides less reaction force compared to a hard surface. This smaller reaction force results in less upward acceleration and a lower jump.

48. How does Newton's Third Law explain the flight of birds?

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.

49. How does Newton's Third Law explain the phenomenon of jet propulsion?

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.

50. How does Newton's Third Law explain the concept of thrust in swimming?

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.

51. Can you explain how Newton's Third Law applies to the recoil of a cannon?

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.

52. Why do you feel a force pushing you back into your seat when a car accelerates?

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.

53. Why do you feel a force on your hand when you hit a wall?

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.

54. How does Newton's Third Law explain the concept of rocket propulsion in water?

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.

55. Why do you feel a force on your hand when catching a ball?

When catching a ball, you feel a force on your hand due to Newton's Third Law. As your hand exerts a force