Universal gravitation is the name given to the law that Isaac Newton devised to explain the gravitational attraction between two massive bodies. Essentially, it states that the force of gravity is proportional to the sum of the combined mass of the two bodies, divided by the distance between them squared. While Newtonian physics are no longer what modern physicists use, its predictions and accuracy were accurate for objects on Earth.
Newton’s law of universal gravitation demonstrates why the planets orbit the sun, rather than vice versa. The sun has a far greater mass than the planets do, so it pulls them into orbit. Because the law also demonstrates that gravitational pull decreases with increasing distance, it explains why Pluto travels around the sun much slower than the Earth does.
Newton did not discover gravity. He expanded upon the work of Kepler and devised the equation that explained gravity’s effects. However, modern physicists know that Newton's work was incomplete. While Newton's equations work for familiar examples of gravity, such as falling apples and orbiting planets, Einstein demonstrated that gravity works much differently in places such as black holes. Einstein's version of gravity, which is even more accurate than Newton's, is the theory of general relativity.