Newton's laws

Newton's First Law of Motion (Law of Inertia)

An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by a force.

Newton's Second Law of Motion

Force equals mass times acceleration ($F = ma$).

Newton's Third Law of Motion

For every action, there is an equal and opposite reaction.

Inertia

The tendency of an object to resist changes in its state of motion.