As hard as it is to comprehend, (almost) everything in the universe is attracted to everything else. This physical law is not only one of the most well-known but also one of the most important. Newton’s law states that the gravitational force between two masses, m and M, is proportional to the product of the masses and inversely proportional to the square of the distance (r) between them. In formula form, this is written as follows (note: in some texts, the masses of the two objects are written as m₁ and m₂):

G is a constant in nature (also called a universal constant), indicating how strong a gravitational force exists. In other words, the farther away the objects, the less the attraction between the objects.