* Inertia: The Resistance to Change Inertia is a fundamental property of matter. It's the tendency of an object to resist changes in its motion. This means an object at rest wants to stay at rest, and an object in motion wants to stay in motion at a constant speed and direction.

* Mass: The Measure of Inertia Mass is a measure of how much matter an object contains. The more massive an object is, the more inertia it has.

Here's a simple way to think about it:

Imagine pushing a small, lightweight box across a floor. It's relatively easy to get it moving and to stop it. Now imagine pushing a very large, heavy refrigerator across the same floor. It's much harder to get it moving, and much harder to stop it once it's in motion.

The refrigerator has more mass, so it has more inertia. It resists changes in its motion more strongly.

In summary:

* More mass = More inertia

* Less mass = Less inertia