Question

The law that gives a qualitative definition of force is
A. Newton second law of motion
B. Law of inertia
C. Newton’s third law of motion
D. Law of gravitation

Answer 1

Hint: Remember concept of inertia. Inertia is nothing but disturbance or resistance to change. Force is nothing but pressure per unit area. You can relate all the examples of Newton's law of motion to day to day life.

Complete Step-by-Step solution:
Newton’s second law:
It states that rate of change of momentum of a body is directly proportional to applied force and takes place in the direction in which force takes.

Newton’s third law:
It states that every action has an equal and opposite reaction.

Newton’s first law/ law of inertia:
Law of inertia is nothing but the first law of newton’s and it gives a qualitative definition of force. Because force must push, pull and make objects move and bring them into motion also. Hence it is a qualitative definition of force.
Every body continues to be in its state of rest or of uniform motion in a straight line unless compelled by some external force to act otherwise. The state of rest or uniform linear motion imply zero acceleration. The first law of motion can. Therefore it simply expresses as “if net external force on the body is zero, its acceleration is zero. Acceleration can be non-zero if there is net external force on the body”.

So the answer is LAW of INERTIA.
Correct option is (B)

Note: In the second and third law of newton, things are going on after force is applied. Means laws are stated when force is applied on the body. the second and third law do not state anything if the body is at rest. Body does not change its motion unless and until external force is applied to it. This comes under classical mechanics. Quantum mechanics is another interesting field where we deal with particles.