Does this equation F= ma (Newton's famous second law of motion) actually tell us anything? When I was studying physics at college I realised that every time we used this equation, a couple of lines of algebra later it seemed we'd always divide throughout by the object's own mass and find out it's equation of motion. Amazing Or is it? Weren't we really just adding the all the acceleration vectors together to find out the object's path ? (Not amazing) If so, then that F = ma law isn't adding any new information whatsoever to the laws of motion, and the whole thing of Newton's 2nd law is an illusion. Aren't Galileo's principle of inertia (1st law), and the conservation of momentum (3rd law) all that we really need to do physics ?