WEBVTT - How do satellites orbit the Earth?

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<v Speaker 1>Welcome to brain Stuff from house Stuff works dot com

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<v Speaker 1>where smart Happens. Hi Am Marshall Brain with today's question,

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<v Speaker 1>how do satellites orbit the Earth? Satellites are to some

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<v Speaker 1>degree mysterious objects. They travel in space, which feels like

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<v Speaker 1>an exotic place because most of us have never been there.

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<v Speaker 1>They're so far away we can't see them. They usually

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<v Speaker 1>cost millions or billions of dollars, which means none of

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<v Speaker 1>us will ever own one personally, and so on. Orbital

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<v Speaker 1>mechanics can also be mysterious because there's no easy way

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<v Speaker 1>for us to experience orbital mechanics personally. However, with a

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<v Speaker 1>little imagination, you can understand the basic idea behind orbital

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<v Speaker 1>mechanics very easily. Think about what happens when you throw

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<v Speaker 1>a ball. Imagine that you're standing in a big field

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<v Speaker 1>and you throw a baseball as hard as you can,

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<v Speaker 1>like a picture. The ball might go a hundred feet

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<v Speaker 1>and then hit the ground. You put the ball into orbit.

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<v Speaker 1>It's just that the ball's orbit is very very short. Now,

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<v Speaker 1>imagine that you shot a rifle straightened level instead of

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<v Speaker 1>throwing a ball. The bullet might travel a mile before

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<v Speaker 1>succumbing to gravity and hitting the ground. Now, imagine that

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<v Speaker 1>you shoot a very large and powerful cannon that's able

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<v Speaker 1>to give its shell an extremely high initial velocity. Imagine

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<v Speaker 1>that the cannon is shot straight and level. The shell

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<v Speaker 1>is going to go many miles far enough to actually

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<v Speaker 1>follow the curve of the Earth for a period of

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<v Speaker 1>time before hitting the ground. One thing that gums these

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<v Speaker 1>examples up is air resistance. So imagine that you took

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<v Speaker 1>this powerful cannon to the Moon and you mounted it

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<v Speaker 1>on top of the highest mountain. The Moon has no

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<v Speaker 1>real atmosphere and is completely surrounded by the vacuum of space.

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<v Speaker 1>If you adjusted the speed of the shell just right

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<v Speaker 1>and shot the cannon, the shell would follow the curve

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<v Speaker 1>of the Moon perfectly. It would fall at exactly the

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<v Speaker 1>same rate that the curve of the Moon falls away

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<v Speaker 1>from it, so it would never actually hit the ground. Eventually,

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<v Speaker 1>it would curve all the way around the Moon and

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<v Speaker 1>ram right into the back of the cannon. On the Moon.

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<v Speaker 1>You could actually have satellites in extremely low orbits like

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<v Speaker 1>that just a few miles off the ground to avoid

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<v Speaker 1>the mountains, and the satellites could conceivably be launched from

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<v Speaker 1>powerful cannons on Earth. It's not so easy, because satellites

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<v Speaker 1>have to get up above the atmosphere and into the

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<v Speaker 1>vacuum of space to orbit for any length of time.

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<v Speaker 1>Two miles up is about the minimum to avoid atmospheric interference.

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<v Speaker 1>The Hubble Space Telescope orbits at an altitude of three

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<v Speaker 1>hundred eighty miles or so, but the principle is exactly

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<v Speaker 1>the same. The speed of the satellite is adjusted so

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<v Speaker 1>that it falls to Earth at exactly the same rate

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<v Speaker 1>that the curve of the Earth falls away from the satellite.

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<v Speaker 1>The satellite is perpetually falling, but it never hits the ground.

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