Gravity
From Aetilc
Gravity is, quite simply, the force that holds together the universe. People are accustomed to thinking of it purely in terms of the gravitational pull Earth exerts on smaller bodies—a stone, a human being, even a Moon—or perhaps in terms of a Star's gravitational pull on a planet. In fact, everything exerts a gravitational attraction toward everything else, an attraction commensurate with the two body's relative mass, and inversely related to the distance between them. The earliest awareness of gravity emerged in response to a simple question: why do objects fall when released from any restraining force? The answers, which began taking shape in the sixteenth century, were far from obvious. In modern times, understanding of gravitational force has expanded manyfold: gravity is clearly a law throughout the universe—yet some of the more complicated questions regarding gravitational force are far from settled.
Gravitation Force of attraction that is exercised by every particle of matter as a result of its mass. Gravitation is the weakest of the four fundamental forces, but it is apparent because of the great mass of the Earth. The Moon has only 1/6 of the Earth's gravitational force. Gravitation was first described (1687) by Sir Isaac Newton, whose law of gravitation stated that gravitational force is directly proportional to the masses of the interacting bodies and inversely proportional to the square of the distance between them. Thus, the gravitational force will decrease by 1/4 if the distance between two objects is doubled. Albert Einstein developed a more complete treatment of gravitation, showing in his general theory of relativity that gravitation is a manifestation of space-time.
In worldbuilding, gravity can be calculated using this equation:
g = M/R^2
