Newton's First Law of Motion (also called the Law of Inertia) states: "An object at rest will remain at rest, and an object in motion will continue in motion with the same speed and direction unless acted upon by an unbalanced external force." Key Points: If no external force acts on an object, its velocity remains constant. This means a stationary object won't move, and a moving object won't stop or change direction unless something causes it to. This law explains why seat belts are important: