The gravitational force is a force that attracts any two objects with mass. The gravitational force is attractive because it always tries to pull masses together, it never pushes them apart. In fact, every object, including you, is pulling on every other object in the entire universe! This is called Newton's Universal Law of Gravitation. However, you don't have a very large mass and so, you're not pulling on those other objects much. Also, objects that are really far apart from each other don't pull on each other noticeably either. But the force is there!

Universal Gravitation Equation

The equation that describes the gravitational force between two bodies is the following:

F_G = G m₁m₂/r²

where F_G is the gravitational constant, G is the gravitational constant, m₁ and m₂ are the masses of the two bodies, and r is the distance between their centers.

The two masses, m₁ and m₂, will exert the same gravitational force on each other.

Figure 1: The gravitational force between two objects of mass m₁ and m₂ separated by a distance r.

So if you know the masses of the two objects are and how far apart they are, you can calculate the gravitational force between them.

Notice that the distance r on the bottom of the equation is squared. This makes it an inverse square law. Because of this, if you double the distance between two objects, you reduce the gravitational force between them to a quarter of what it was.

On the other hand, since the gravitational force is directly proportional to the mass of both interacting objects, more massive objects will attract each other with a greater gravitational force. So as the mass of either object increases, the force of gravitational attraction between them also increases.