The **Law of Universal Gravitation** explains that gravitational force decreases with distance. In addition, the theory notes that the greater an object's mass, the greater its gravitational force. Newton published his argument in *Philosophiae Naturalis Principia Mathematica* (1687). It is important to note that Newton was not "inventing" or "discovering" gravity; he was merely defining it mathematically. Newton would use universal graviation, along with his laws of motion, to substantiate Kepler's laws of planetary motion.

*Every object in the Universe attracts every other object with a force directed along the line of centers for the two objects that is proportional to the product of their masses and inversely proportional to the square of the separation between the two objects.**Two bodies attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.*

- F = gravitational force between two objects
- m
_{1}= mass of first object - m
_{2}= mass of second object - r = distance between the objects
- G = universal constant of gravitation