CBSE Class 11 Physics Newtons Laws Of Motion Notes Set B

NEWTON’S LAWS OF MOTION

Newton’ 1st law or Law of Inertia

Every body continues to be in its state of rest or of uniform motion until and unless and until it is compelled by an external force to change its state of rest or of uniform motion.

Inertia

The property by virtue of which a body opposes any change in its state of rest or of uniform motion is known as inertia. Greater the mass of the body greater is the inertia. That is mass is the measure of the inertia of the body.

Numerical Application

    →        →

If, F = 0 ; u = constant

Physical Application

1. When a moving bus suddenly stops, passenger’s head gets jerked in the forward direction.

2. When a stationery bus suddenly starts moving passenger’s head gets jerked in the backward direction.

3. On hitting used mattress by a stick, dust particles come out of it.

4. In order to catch a moving bus safely we must run forward in the direction of motion of bus.

5. Whenever it is required to jump off a moving bus, we must always run for a short distance after jumping on road to prevent us from falling in the forward direction.

Key Concept

In the absence of external applied force velocity of body remains unchanged.

Newton’ 2nd law

Rate of change of momentum is directly proportional to the applied force and this change always takes place in the direction of the applied force.

dp / dt αF

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