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Author Topic: Can unwanted gas be sucked off Earth with a straw?  (Read 2625 times)

Offline Eric A. Taylor

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The team was asked this question in this weeks podcast. They answered correctly in saying that if you stuck a straw from the ground into space you'd have a straw with air at a pressure of around 30 in Hg at the bottom and a vacuum at the top. They went a little wrong in suggesting you might be able to pump the air into space but This wouldn't help. Air, like all other matter has mass. (This is why it's held to Earth by gravity) if you pumped it to the top of the pipe it would simply fall back to Earth, unless you pumped the air to escape velocity, which is really hard to do.

Air can be knocked into space by an impact. Very often when you see animations of impacts on TV they will show a huge splash of molten rock being thrown up into space. This also happens to the air. If you went into the impact ground zero very soon after the impact (within a few seconds but I'd strongly recommend you don't do this) you'd find a vacuum. Much of the air is thrown into space where it might reach heights of several thousand miles (the space shuttle only orbits about 300 miles up). It will then fall back onto the Earth about the same time and all the rock get's back.

In the book by H.G. Wells From the Earth to the Moon one of the people invents a martial that blocks gravity, very much like an iron plate blocks light. A plate of this stuff falls over and the air above the plate shoots upward. The air next to the plate zooms in to fill the vacuum but it too shoots upward, creating a huge implosion that causes quite a lot of damage. This is just what would happen. However if the air has any sideways motion (which it would from the rush to fill the vacuum) that motion would carry it across the plate and the air would begin to fall again. This would keep the implosion going forever unless some could get the the plate to turn it side on again.

If our understanding of gravity is correct then no material with mass would be able to block gravity though. (the book was written several years before Relativity).


 

Offline daveshorts

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Can unwanted gas be sucked off Earth with a straw?
« Reply #1 on: 14/04/2010 10:07:35 »
You could however pump it up high enough to be blown away by the solar wind, which is what I was trying to say, though it was a bit rushed.
 

Offline Eric A. Taylor

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Can unwanted gas be sucked off Earth with a straw?
« Reply #2 on: 16/04/2010 06:14:24 »
If you pumped it to an altitude of over 25,000 miles it will be slung off by the force of Earth's rotation.

  However building a pipe this long out of conventional material (even the lightest, strongest stuff available)would be so heavy it would break through the Earth's crust. A 25,000 mile long pipe, if it fell down, would wrap around the equator more than once (over a period of 2 or three days) leading to quite a lot of excitement.
 

Offline daveshorts

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Can unwanted gas be sucked off Earth with a straw?
« Reply #3 on: 16/04/2010 09:01:26 »
Yes not very practical :)
 

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Can unwanted gas be sucked off Earth with a straw?
« Reply #3 on: 16/04/2010 09:01:26 »

 

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