Isaac Newton proposed the three laws of motion and the law of universal gravitation.
Newton presented these ideas in Philosophiæ Naturalis Principia Mathematica, usually called the Principia, published in 1687. The work established a mathematical framework for explaining motion on Earth and the movements of planets and moons in space.
His first law describes inertia, the second relates force to the rate of change of momentum, and the third states that interacting bodies exert equal and opposite forces. His law of universal gravitation explained why objects fall and why celestial bodies follow orbits.
Newton’s achievement built on earlier work by Galileo Galilei and Johannes Kepler. He also made major contributions to optics and calculus, though the independent development of calculus by Gottfried Wilhelm Leibniz remains an important historical distinction. Einstein’s relativity later extended, rather than simply erased, Newtonian mechanics.