# State of a Body and Inertia

State of a body:

A body can be either at rest or in motion. A body is said to be in motion if it’s position does not change with respect to its surrounding. For example: A chair is at rest with respect to the object in the room.

A body is said to be in motion if it changes its position with respect to its surrounding. For example: A bus is moving in a road, car is moving in a circular path etc.

Note: The concept of rest and motion above explained is fully based on classical mechanics developed by Newton.  It is an old concept.

Force: A force is a pull or push of an agency which tends to change the position of a body at rest, in motion or even direction of a moving body. Example magnetic force, fricitional force, gravitational force etc.

Mass:  It is the amount of matter contained in it. It is independent of physical conditions.

Inertia: It is the tendency of a body to remain in its original position unless an external force is applied on it. The book continues to be the table until external force is applied to remove it from rest position.

Inertia of rest: The inability of a body to remain in the state of rest unless an external force is applied on it is called inertia of rest.  Exmple

Inertia of motion: The inability of a body to remain in the state of motion unless an external force is applied on it is called inertia of motion. Exmple

Inertia of direction: The inability of a body to change its direction of motion by itself is called inertia of direction. Example

Mass is the measure of inertia:

We know that when we apply force to a small object of less weight, it moves. But if we try to move a large stone by applying same amount of force, the stone remains in its own position. Here, we conclude that mass is the measure of inertia.

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