Newton’s laws [Sir Isaac Newton, English physicist, 1643–1727] , laws of motion first published by Isaac Newton. Newton’s first law states that bodies at rest stay at rest and bodies in motion keep moving unless they are acted on by an unbalancing force. The second law is that the greater the mass of an object the greater the amount of force needed to accelerate the object. Newton’s third law states that every action force has a reaction force that is equal in magnitude but opposite in direction. See also kinetics, def. 1.
