Inertia

Inertia is the tendency of a body to maintain its state of rest or of uniform motion on its own or we can say that it is the inability of a body to change its state of rest or of uniform motion on its own.

Inertia and mass : Consider two bodies of unequal masses, say a table tennis ball and a cricket ball. If both balls are pushed with equal force for the same time, a cricket ball will have much smaller velocity as compared to the tennis ball. Cricket ball has resistance more than table tennis ball. Or, cricket ball has larger inertia than table tennis ball. So, we can generalise, a heavier body has a larger inertia than a lighter body. Same is true for objects in motion also. If you have to stop a lighter body and a heavy body moving with equal velocities, you may stop the lighter body with your hands (depending on its velocity), while the heavier one may slow down only a little (depending on its velocity).

Larger the mass, larger is the inertia. Hence, may say mass is a measure of inertia,