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Question 3: Explain Newton’s Laws of motion. Give examples in each case for further elaboration. Answer

Newton’s First Law of Motion

In the absence of an external unbalanced force, if a body is at rest, will remain at rest, and if moving with uniform velocity, will continue to do so for ever. Now if a body is under the influence of a number of forces,vecf1vecf2, …,fn. If the sum of the forces is zero, there would be no unbalanced or net force acting on the body.

∑F = Fnet = 0

The law states that under such conditions, the body will not change its state of rest or uniform motion. So the acceleration will be zero. Hence,

Newton first law

Example (1) The ball hit off the bat of a batsman goes high in the air. After some time, it stops its upward motion and starts falling. It is because the force of friction due to air is continuously acting on it, till it comes to stop. (2) If you keep your books in the bag it will remain there until you (or someone else) come to pick it.

Newton’s Second Law of Motion

When a certain net force is acting on a body, it produces acceleration in the body in its own direction. Moreover, the acceleration thus produced varies directly with the force and inversely with the mass of the body.

Newton second law

Where vecF and veca smallhave the same direction. When the direction of motion of body and the net force acting on it is the same, acceleration is said to be positive and the body speeds up. On the other hand, if the direction of motion and the direction of applied force are is opposite, the acceleration is negative and the body slows down. Example When a footballer kicks the ball, we can see easily that;
  • The ball goes faster if it is kicked harder and vice-versa. This means the acceleration produced is directly proportional to the applied force.
  • The ball goes in the same direction in which it is kicked. This means the applied force of the kick produces acceleration in its own direction

Newton’s Third Law of Motion

It states that for every action there is always an equal but opposite reaction. Let we have two bodies A and B. Body A exerts a force vec Fabon body B. The law states this force of A on B, vec Fab is the action of A on B. As a result, body B will also exert an equal opposite force vec Fba on body A. This force is called the reaction of B on A. So, according to the law,

vec Fab = –vec Fba

  • A direct conclusion of the law is that action and reaction always occur in pairs.
  • Action and reaction never neutralize one another. They act on two different bodies. Only those equal forces balance one another which act on the same body.
Example When we walk, we push the earth in the backward direction. As a result we are pushed by the earth in the forward direction.

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