What is inertia ? Define and explain three different types of inertia.

Explanation

Inertia: It is the inability of a body to change its state by itself.
Or
It is the inherent property of a body by virtue of which it always opposes any change in its state (rest or uniform motion).
i) Inertia of rest: The property of a body due to which it cannot change its state of rest is known as inertia of rest. For example, when a horse suddenly starts moving, the rider falls backwards. This happens because lower part of body comes into motion, but due to inertia of rest upper part tends to be at rest.
ii) Inertia of motion : The property of a body due to which it cannot change its state of motion is known as inertia of motion. For example, when a horse suddenly stops, the rider falls in forward direction. This happens because lower part of body comes into rest whereas upper part of body remains in motion.
iii) Inertia of direction
The property of a body due to which it cannot change its direction of motion is known as inertia of direction. For example, the sparks coming out of a knife are tangential to the rotating grinding stone. The happens due to inertia of direction.