Newton's 1st Law
Inertia
Definition
Objects in motion will stay in motion and an object at rest will stay at rest until acted upon by any outside force. All objects resist changing their motion. This tendency in motion is called inertia. The more mass an object has, the greater the inertia.
Inertia and Mass
The tendency of an object to resist changes in its state of motion varies with mass. Mass is that quantity that is dependent upon the inertia of an object. The more inertia that an object has, the more mass that it has. A bigger object has a greater tendency changing their state of motion.
Examples
Further Information
Newton's 1st Law of Motion