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Meet the Universe's
Main Attraction...
Gravity

If you throw a ball into the air, it will return to the ground. Why?

Earth has invisible pulling power called gravity. In fact, our planet isn’t the only place with gravity. Every object in the universe — stars, planets, moons, even you—has gravity.

Gravity is a force of attraction between all objects.

Isaac Newton

How does gravity work? There are two ideas you need to know. These ideas work throughout the universe.

1. The more massive  an object is, the more gravity it has.

2. The closer two objects are, the stronger the gravitational pull between them.

So, putting these rules together, the more massive and the closer two objects are, the greater the gravitational attraction between them.

What does gravity do?

Earth’s gravity pulls you back to the ground when you jump in the air. Otherwise, you’d fly out into space.

Earth’s gravity pulls you back to the ground when you jump in the air. Otherwise, you’d fly out into space.

The Sun’s powerful gravity keeps Earth  in orbit around it.

The Sun’s powerful gravity keeps Earth  in orbit around it.

Gravity pulls stars  and planets into round shapes called spheres. Did you ever see a square planet?

Gravity pulls stars  and planets into round shapes called spheres. Did you ever see a square planet?

What would happen if...?

To understand the universe, scientists sometimes do “ thought experiments ”. They take a familiar situation and ask, “What would happen if we changed something about it?” Then they apply the laws of the universe and see how the situation would be different.

Try a thought experiment!

Look at this picture of a carnival. Then ask yourself: What would happen if the force of gravity were suddenly “turned off” in the whole universe?

Try a thought experiment!

Look at this picture of a carnival. Then ask yourself:  What would happen if the force of gravity were suddenly “turned off” in the whole universe?

##### Image Credits:
apple background pattern, Amanda Zaldivar; baseball, © AMNH; Isaac Newton, by Amanda Duffy; landing feet, by Jim Paillot; Earth orbiting the Sun, by Jim Paillot; planets and gravity, by Jim Paillot; circus scene, by Chris Van Dunsen.