Here's why:

* Definition of Inertia: 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.

* Force and Inertia: Forces are what *cause* changes in motion. Inertia is the inherent resistance to those changes. Think of it like this:

* Force: The push or pull that tries to change motion.

* Inertia: The object's "stubbornness" in resisting that change.

* Example: Imagine pushing a heavy box. The box's inertia is what makes it hard to get moving. Once it's moving, its inertia makes it hard to stop.

In summary: Inertia is a fundamental property of all matter, describing its resistance to changes in motion. Forces are what interact with matter, causing those changes.