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WHAT DOES NEWTON’S THIRD LAW TEACH US?

Newton gave out three laws which laid the foundation for the classical mechanics. The laws collectively describe the relationship between the body and the forces that act upon it along with its motion in response to the forces.


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Newton gave out three laws which laid the foundation for the classical mechanics. The laws collectively describe the relationship between the body and the forces that act upon it along with its motion in response to the forces.

The first law basically describes the force qualitatively; the second law gives a quantitative measurement of the force; and the third law asserts that there is absence of a single isolated force.

The three laws were compiled by Isaac Newton in 1687. He used them to investigate and explain the motion of varied physical objects and systems.

THE THIRD LAW

Newton’s third law of motion states – for every action, there is always an equal and opposite reaction.

F1= -F2

The action and reaction always acts on different and varied objects. The law indicates that whenever an object exerts force on another object, the latter object immediately and instantaneously applies a reactive force on the first object. The two forces (action and reaction) are always equal in their magnitude but are always opposite in direction. Since the forces act on different objects, they do not cancel out each other. Newton’s third law, thus, establishes the interaction of forces between the two objects.

Action is the force exerted by the first object on the second object while reaction is the force exerted by the second object on the first object in response to the action.

The third law of motion establishes-

  • Size of the force on object 1 is always equal to the size of force on object 2.
  • The direction of force on object 1 is opposite to the direction of force on object 2.
  • There is no isolated force. Force comes in pairs. Equal and opposite – action and reaction.

APPLICATIONS OF THE THIRD LAW OF MOTION

  • When a bullet is fired from the gun, a force is exerted by the gun in the forward direction, called the action force. The bullet also exerts a reaction force on the fun, equal in magnitude, but opposite in direction. As the mass of the gun is large, it only moves back a little distance, giving a jerk on the shoulder of the person using the gun. This movement of the gun is called recoiling of the gun. This explains why the gun recoils when a bullet is fired from it.
  • The action of the rocket is to push downwards on the ground and the reaction of the ground is that it pushes the rocket upwards.