1. : a statement in dynamics: a body at rest remains at rest and a body in motion remains in uniform motion in a straight line unless acted upon by an external force — called also Newton's first law of motion
2. : a statement in dynamics: the acceleration of a body is directly proportional to the applied force and is in the direction of the straight line in which the force acts — called also Newton's second law of motion
3. : a statement in dynamics: for every force there is an equal and opposite force or reaction — called also Newton's third law of motion