Here's why:
* Inertia is 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.
* Velocity is a measure of both an object's speed and direction.
* Change in velocity can be a change in speed, a change in direction, or both.
Therefore, inertia is the property that resists any change in velocity, whether that change is a change in speed, a change in direction, or both.
