The force of gravity between two objects will decrease as the distance between them increases. The two most important factors affecting the gravitational force between two objects are their mass and the distance between their centers. As mass increases, so does the force of gravity, but an increase in distance reflects an inverse proportionality, which causes that force to decrease exponentially.
The inverse relationship between the force of gravity and the distance between two objects is based on the square of that distance. This means that if the distance is doubled, the gravitational force is decreased by a factor of 4. This is because the square of 2 is 2 x 2, which equals 4. If the distance between two objects is tripled, the force of gravity is decreased by a factor of 9. In this case, it is because the square of 3 is 3 x 3, which equals 9. This relationship is known as the inverse square law.
The inverse-square law of universal gravity was developed in 1687 by the English mathematician and physicist Sir Isaac Newton. It later led to the prediction by two separate mathematicians that another planet existed beyond Uranus, which was the farthest known planet at that time. Deviations in Uranus's orbit could only be accounted for by the gravitational pull coming from a still undiscovered planet. The calculations made by one of the mathematicians resulted in astronomer Johann Gottfried Galle directing a telescope to the predicted location of the unknown planet and discovering the planet Neptune.