- And now, here's my friend, astronomer Amy Mainzer.

- Thanks, Jet.

Have you ever heard the saying, what goes up must come down?

So why doesn't this water balloon just keep going up when I toss it?

Ohh!

The balloon landed with a splat because Earth's gravity brought it right to the ground.

Gravity's a force that pulls one thing toward another.

Things that are big tend to have more gravity than things that are small.

The Earth is way, way, way bigger than either me or the water balloon.

So it pulls both of us down pretty strongly.

But not everything in space is as big as the Earth.

The Moon is a lot smaller than the Earth, so it has less gravity than Earth does.

If I were on the Moon, I could jump a lot higher.

And I'd come down a lot slower.

If I were on something even smaller than the Moon, like, say, a space rock called an asteroid, I might even be able to jump so high I could launch myself right into space.

But back here on Earth, gravity keeps me firmly on the ground.

But wouldn't it be great if I could just have some Bortronian technology that would turn it off?

- Thanks, Amy!

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