In physics, an object's tendency to keep doing what it is doing is called inertia.

Here's a breakdown:

* Inertia: The property of matter that resists changes in motion. This means an object at rest wants to stay at rest, and an object in motion wants to stay in motion at a constant speed and direction.

* Newton's First Law of Motion (Law of Inertia): This 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 an unbalanced force.

Think of it this way: imagine a book sitting on a table. It's at rest. It will stay at rest unless you push it, pull it, or otherwise apply a force to it. Similarly, a ball rolling across a smooth floor will keep rolling unless something like friction or a wall stops it.