* Inertia: Inertia is the tendency of an object to resist changes in its motion. This means it wants to stay at rest if it's at rest, or continue moving at a constant velocity if it's already moving.

* Mass: Mass is a measure of the amount of matter in an object. It's a fundamental property that determines how strongly an object interacts with gravity.

The connection:

* Mass is a measure of inertia. The more massive an object is, the harder it is to change its motion. Think of it this way: a bowling ball is much harder to push and get moving than a tennis ball, even though they might be moving at the same speed. The bowling ball has more inertia because it has more mass.

* Inertia is directly proportional to mass. This means if you double the mass of an object, you also double its inertia.

Newton's First Law of Motion encapsulates this relationship:

* An object at rest stays at rest, and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

This law emphasizes that inertia is the inherent property of an object that resists changes in its state of motion, and that mass is the quantifiable measure of this resistance.