Newton's laws cannot be proven!! As far as i know, Newtons laws are..... 1st Law-- A body at remains at rest and a body at uniform motion remains at uniform motion unless an external for acts on it. 2nd Law-- F=ma 3rd Law-- Every action has an equal and opposite reaction. No method has been designed to prove these three laws. However, these laws are vital in almost the whole of physics. I heard that we believe in these laws because all the measurements and experiments are in agreement with these laws.. What does this exactly mean? Can somebody give an example. Also, as far as i know, 1st and 2nd law hold only in inertial frame of reference and Newtonian mechanics does not work when the speed of any object approaches the speed of light. Does the 3rd law still work in an accelerating frame of reference and when the speed of the object approaches the speed of light? If yes then why so? It would be great if someone could give me an answer.