The English physicist Isaac Newton introduced the term "gravity" after he saw an apple falling onto the ground in his garden. "Gravity" is the force of attraction exerted by the earth on an object. The moon orbits around the earth
and the earth orbits around the sun because of gravity. Newton proposed that
every mass in the universe attracts every other mass. This is the main idea of Newton's Law of Universal Gravitation.
The law was published in Newton's famous work, the Principia ("Mathematical Principles of Natural Knowledge") in 1687. It states that:
Every particle in the universe exerts a force on every other particle along the line joining their centers. The magnitude of the force is directly proportional to the product of the masses of the two particles, and inversely proportional to the square of the distances between them.
Newton's Law of Gravity Calculator
Simulator courtesy of University of Nebraska-Lincoln