Here's why:

* 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 the same speed and direction.

* Inertia is directly proportional to mass. The more massive an object, the harder it is to change its motion (i.e., the greater its inertia).

Let's illustrate this:

Imagine a bowling ball and a tennis ball. Both have inertia, but the bowling ball has much more mass and therefore much more inertia.

* If you push both with the same force, the tennis ball will accelerate much more easily than the bowling ball.

* If they're both moving at the same speed, it will take more effort to stop the bowling ball than the tennis ball because it has more inertia.

Speed does not influence the inherent inertia of an object. It's like saying a heavier person is harder to move whether they're standing still or walking. Their mass, not their speed, determines how much they resist being moved.