Inertia is a property of matter by which it remains at the state of rest or in uniform motion in the same straight line unless acted upon by some external force. In other words, it is the tendency of a body to resist any change in its state of motion. The following are the types of inertia:

• Inertia of rest: The tendency of a body to remain in the state of rest.
• Inertia of motion: The tendency of a body to remain in uniform motion in the same straight line.
• Inertia of direction: The tendency of a body to remain in a particular direction.

For example, when a person tries to push a big table, it is difficult to move it because the table has a large inertia of rest. Similarly, when a car rounds a curve suddenly, the driver is thrown outside because of the inertia of direction.