| Noun | 1. | Newton's law of motion - one of three basic laws of classical mechanics law of nature, law - a generalization that describes recurring facts or events in nature; "the laws of thermodynamics" first law of motion, Newton's first law, Newton's first law of motion - a body remains at rest or in motion with a constant velocity unless acted upon by an external force Newton's second law, Newton's second law of motion, second law of motion - the rate of change of momentum is proportional to the imposed force and goes in the direction of the force law of action and reaction, Newton's third law, Newton's third law of motion, third law of motion - action and reaction are equal and opposite |