We all understand that if we hold something up in the air and then let go, it will fall to the ground. Things fall because of gravity. Gravity is an attractive force between all things that have mass. It is one of the fundamental forces of nature. Gravity causes objects with mass to accelerate towards each other. The rate of acceleration depends on the mass of the objects and their proximity. The more mass an object contains, the more it will attract other objects. The closer an object is to another the greater the attraction between them will be.