Are Newton's three laws of motion correct as Netwon stated them? 1. The first law is the principle of inertia. It states that an object in motion will continue to move unless acted on by an external force. And that an object at rest will remain at rest unless acted on by an external force. 2. The second law states that the change in momentum is proportional to the external force. 3. The third law is that for every action there is an equal and opposite reaction.