Here's why:
* Inertia is the tendency of an object to resist changes in its motion. This means an object at rest will stay at rest, and an object in motion will stay in motion at a constant velocity unless acted upon by a net force.
* Mass is a fundamental property of matter that measures its resistance to acceleration. The more massive an object is, the harder it is to get it moving or to stop it once it is moving.
Therefore, mass is directly proportional to inertia. A more massive object will have more inertia, making it harder to change its state of motion.
