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World Book at NASA for Students

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Drawings of a boy jumping high in the air on Earth. In the middle is boy in space suit jumping higher on the moon. On right is boy in suit jumping only about 35 centimeters or 14 inches on Jupiter.
Gravity is a force that causes things to fall when they are dropped. The force of gravity gives things their weight.

Every object has its own force of gravity. Earth's gravity keeps the moon on its path around Earth. The moon has its own gravity, but it is not as strong as that of Earth. That is why astronauts on the moon can carry equipment that would be too heavy to carry on Earth.

Image to left: Some planets have a stronger force of gravity than others. On Earth, above left, you might be able to jump 3 feet (almost 1 meter). On the moon, center, which has low gravity, you might jump 20 feet (6 meters). On Jupiter, above right, which has high gravity, you could jump only 14 inches (35 centimeters). Credit: World Book illustration

Gravity depends on the amount of material that makes up an object. The more material an object has, the stronger is its force of gravity. The force of gravity between two objects decreases as the objects get farther apart.

How to cite this article: To cite this article, World Book recommends the following format: "Gravity." The World Book Student Discovery Encyclopedia. Chicago: World Book, Inc., 2005.

 
 
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