Page 1
A Powerful Force
Stand outside and look around.
The ground lies beneath your feet. The sky stretches above your head.
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You are standing on Earth. Our planet is like a giant ball floating in space.
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Now think about kids standing on the other side of Earth. The ground lies beneath their feet. The sky stretches above their heads.
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How can that be?
What keeps these
kids from falling
off Earth?
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A force called gravity pulls the kids toward the ground. It keeps them from flying into space.
Page 6
Gravity works on everybody and everything. You can't see gravity, but it is a basic part of nature.
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How Gravity Works
Gravity is a powerful force of attraction. It tries to pull two things together.
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Look around your room.
Every object in it is affected by gravity.
Your pencils, shoes, books, clothes,
and bed are pulling at
each other. So why
aren't your pencil
and eraser flying across
your desk to meet?
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Small objects, such as pencils, erasers, and ants, have a very weak pull of gravity.
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Large objects pull much more strongly. The heavier an object, the harder it will pull.
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Earth's Gravity
Earth is bigger than the houses, trees, people and everything else on it.
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Earth's gravity is strong enough to keep your home sitting on the ground. It is strong enough to keep the tree you like to climb from drifting away.
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Jump up! Earth's gravity
quickly pulls you down.
Throw a ball, and
it falls down.
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Gravity also makes rain fall to the ground. It makes leaves drift down from trees.
Page 15
Gravity in Space
Gravity also works in outer space. Planets, moons, and stars pull on each other.
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Smaller objects often orbit, or travel around, bigger objects. Earth orbits the sun. The moon orbits Earth. Gravity keeps everything in place.
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Earth's gravity is stronger than the moon's.
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So if Earth is
pulling on the
moon, why doesn't
the moon come
crashing down?
Page 19
The moon never stops speeding around Earth. The moon's speed keeps it from crashing into our planet.
Page 20
Use a yo-yo to see how the moon stays up. Spin the yo-yo in a circle around you. The yo-yo only drops when it stops moving.
Page 21
Perfect Gravity
Jump. Skip. Kick a ball! Earth's gravity is just the right strength for your body.
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If you lived on a planet as big as Jupiter, it would be hard to even lift your foot from the ground!
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So next time you take a big leap high in the air, think about gravity before you land on the ground!
