Newton's first law

And Inertia

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 an unbalanced force acts upon it.

Inertia: The resistance of any physical object to any change in its state of motion including changes to its speed and direction or the state of rest. It is the tendency of objects to keep moving in a straight like at constant velocity.