Britannica Sources used in this answer

How did Newton use gravity to explain the motion of planets?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

A diagram of a cylindrical vessel containing gas, with a movable piston held down by a weight. Countless small dots beneath the piston represent gas particles in rapid, random motion, illustrating Bernoulli's model of gas pressure. — physics As conceived by Daniel Bernoulli in *Hydrodynamica* (1738), gases consist of numerous particles in rapid random motion. He assumed that the pressure of a gas is produced by the direct impact of the particles on the walls of the container.

Isaac Newton revolutionized our understanding of the cosmos by demonstrating that the same gravity pulling objects to Earth also governs the motion of planets.12

Newton utilized Kepler’s laws of planetary motion—which describe how planets move in elliptical orbits—to derive his law of universal gravitation. By applying his three laws of motion, Newton reasoned that a planet would naturally travel in a straight line due to inertia. However, because planets follow curved paths, a continuous, inward-pulling centripetal force must be acting upon them.3456

Newton mathematically demonstrated that for this motion to occur, the force must decrease with the square of the distance between the planet and the Sun. He confirmed this by showing that the same inverse-square relationship applied to the Moon orbiting Earth. This synthesis of mathematics and physical observation, published in his seminal work, the Principia, established the foundation of classical mechanics and provided a unified explanation for both terrestrial and celestial phenomena.62