The early Greeks established the first quantitative physical laws, such as Archimedes' descriptions of the principle of levers and the buoyancy of bodies in water. But they did not actually conduct experin ents, and physics as science stagnated for many centuries. By the 17th century, however, Galileo Galilei and later Issac Newton helped pioneer the use of mathematics as a fundamental tool in physics, which led to advances in describing the motion of heavenly bodies, the laws of gravity and the three laws of motion.