"Galileo first studied the motion of terrestrial objects, pendulums, free-falling balls, and projectiles. He summarized what he observed in the mathematical language of proportions. And he extrapolated from his experimental data to a great idealization now called the “inertia principle,” which tells us, among other things, that an object projected along an infinite, frictionless plane will continue forever at a constant velocity. His observations were the beginnings of the science of motion we now call “mechanics.”... Newton also invented a mathematical language (the "Fluxions" method, closely related to our present-day ) to express his mechanics, but in an odd historical twist, rarely applied that language himself."