law of motion: Meaning and Definition of

law' of mo'tion

1. any of three laws of classical mechanics, either the law that a body remains at rest or in motion with a constant velocity unless an external force acts on the bodythe law that the sum of the forces acting on a body is equal to the product of the mass of the body and the acceleration produced by the forces, with motion in the direction of the resultant of the forcesor the law that for every force acting on a body, the body exerts a force having equal magnitude and the opposite direction along the same line of action as the original forceAlso called