Force and Laws of Motion

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06 Newton’s Third Law of Motion

NEWTON’S THIRD LAW OF MOTION

  • Newton’s third law of motion states that: Whenever one body exerts a force on another body, the second body exerts an equal and opposite force on the first body.
  • It is also stated as: To every action there is an equal and opposite reaction.

SCENARIO OF NEWTON’S THIRD LAW OF MOTION

 

 

If FAB is the force exerted by body A  on B  and FBA is the force exerted by B on A, then according  to the Newtons third law,

 

FBA =  FBAOr        Force on A  by B  = Force on B  by  A  Or              Reaction = Action

 

The two forces shown in the figure are also known as Action Reaction pair.

PROPERTIES OF ACTION REACTION PAIR

  • Both forces are equal in magnitude
  • They act on different bodies i.e. in this case one force is acting on the wall while the other is acting on the person

EXAMPLES TO ILLUSTRATE NEWTON’S THIRD LAW MOTION

How do we walk?

 

When we walk on the ground, our foot pushes the ground backward and, in return, the ground pushes our food forward. This forward reaction exerted by the ground on our foot makes us walk forward.

Why the Gun Recoils?

When a bullet is fired from a gun, the force that sends the bullet forward is equal to the force that sends the gun backwards. But since the mass of the gun is high, , it moves only a little distance backward and gives a backward jerk or kick to the shoulder of the gunman.

The Flying of Jet Aeroplanes and Rockets

Jet aeroplanes work on the principle of action and reaction. Similarly, The rockets also work on the principle of action and reaction.

 

The Case of a Boat and the Ship

During the rowing of a boat, the boatman uses oars to push the water backwards. The water exerts an equal and opposite push on the boat which makes the boat move in the forward direction.

 

The boat moves backward when a person jumps out of it

When a person jumps of a boat, he applies a force on the boat in backward direction. The boat also applies a force on the person which helps him to move forward. As the boat also experiences a force in the backward direction so it moves backward. The force acting on the boat and the person is equal but their masses are different. Hence their acceleration will also be different.

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