How Does Gravity Work?

Newtonian Gravity

Gravity is the force that occurs between two objects with mass. It is commonly thought of as the force which gives objects their weight. Gravity causes matter that is separated to move together, so it is responsible for the planets, the stars and most objects in the universe "sticking" together. Gravity is also the force that keeps planets and moons in the orbit by providing a constant force drawing in these moving objects to what they are orbiting around. Gravity is also what is responsible for keeping objects on the rotating Earth.

Newtonian gravity

In Newtonian gravity, the gravitational force between two objects can be described by a simple equation. The gravitational force is directly proportional to the mass of both objects and is inversely proportional to the square of the distance between them. That means that if either of the two objects increases in size, the gravitational force will get stronger. This also means that as they get farther apart, the force between them weakens, but at a much faster rate. As a result, if you take two objects and double the distance between them, the gravitational force will be one fourth of what it was. It also should be noted that gravity pulls on both objects. As a result, two equally sized planets can have a binary orbit, with both moving around each other in an elliptical shape.

Gravity and Relativity

In Einstein's theory of general relativity, gravity is thought of as a space-time curvature rather than an actual force. Einstein believed that matter can curve space-time. Thus, gravity, instead of drawing masses together, causes them to bend and warp space-time so that they appear to be attracted to each other by gravity. He also proposed that when objects are moving in freefall (similar to falling out of a plane) they move in straight lines called geodesics. These straight lines are then curved by warped space-time.