State of body

1. Rest

A body is said to be at rest if it does not change its position with respect to surrounding.

2. Motion

A body is said to be in motion if it changes its position with respect to surrounding.

Newton’s laws of motion

There are 3 laws of motion, given by Sir Issac Newton. They are:

Newton’s 1^st law of motion:

This law states that, “Everybody continues in its state of rest or uniform motion in a straight line unless it is acted by an external force to change that state.”

The Newton’s first law of motion gives qualitative definition of force and concept of inertia.

Definition of force:

According to Newton’s 1^st law of motion, an inert body has no tendency to change its state by itself. In order to change the state of body, an external agency is required which is called force.

Thus, the force is defined as that external agency which changes or tends to change the state of body.

In this way, the Newton’s 1^st law of motion gives the qualitative definition of force.