The law associated with inertia is Newton's First Law of Motion, also known as the Law of Inertia.

Here's a breakdown:

* Inertia is the tendency of an object to resist changes in its state of motion. This means an object at rest wants to stay at rest, and an object in motion wants to stay in motion at the same speed and direction.

* Newton's First Law states that 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 external force.

Essentially, Newton's First Law defines inertia and explains why objects behave the way they do when forces are applied or not applied to them.