What is inertia

4 (b) state that the mass of a body resists change from its state of rest or motion

Inertia

Ever wondered why it is so difficult to push a larger object, compared to a smaller object? It is much more difficult to push a car along a road, than to push a book along a table. Inertia explains the reasoning behind this.

Inertia is the resistance of a body to change its state of rest or motion. It means that if a body is stationary, it would resist to change its state of rest if it is pushed, or a force is applied on it. It would try to remain stationary, and this resistance is known as Inertia.

The same applies to moving objects. It is the tendency of a moving object to keep moving. A bicycle should keep moving infinitely if pedaled only once according to inertia. But we know this does not happen. Why is it so?

The bicycle stops moving due to the external forces acting on it .If there were no external forces like air resistance, friction etc on it while you were cycling to school, all you would have needed was to pedal your bicycle once, and you could have traveled all the way to your school! 

Inertia depends on the mass of an object. The more the mass of an object, the more resistance it will provide to change its state of rest or motion. That pretty much explains why objects with more mass are difficult to push or stop, compared to smaller objects.