Newton's law of universal gravitation can be applied to two objects.

When we are dealing with systems with more than two objects, we must use the principle of superposition: The force exerted by one object on another is independent of the forces exerted by the other objects.

In sets like the solar system, where most of the mass belongs to only one of the heavenly bodies, the forces between the planets are in many cases negligible.

Click on Next to study a case in which this force should not be neglected. The visual shows a small asteroid moving between the sun and a big planet (Jupiter, for example).