What if you had a huge open-ended pipe (I am thinking gigantic huge!!!!) and, ignoring all the technicalities, were able to hoist it up in the sky so that one end was in outer space and the other was in the earth's atmosphere. would it suck out the air? I mean there would be a pressure gradient so there would be a flow of fluid from high pressure to low pressure. right... right?
What if....
- Thread starter AnandtechPirate
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forrestroche
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- Apr 25, 2005
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Please use technical language in this forum. For "Gigantic huge" pipe please substitute the engineering equivalent: BFP
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well you don't have a vacuum at one end in that case
Hey, I used the word gradient, didn't I? thats sort of technical.
Heh, nothing really to add except to confirm the post above that states gravity will keep the atmosphere in place like it's already doing. It would be interesting to have a "BFP" that was sealed at the ground level though.
yep, when you have a vaccum on one side then there is a force pushing on the water from the bottom, but no force on the top, so the water will rise. However, as it rises, the force of gravity will begin to oppose the force exerted by the pressure gradient, when the 2 forces are equal the fluid will no longer rise.
forrestroche
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Yes, there was partial compliance with terminology protocols. For that reason you were not banned immediated from the Highly Technical forum.
You are a new member and we do not wish to be unreasonable. An example of someone who should know better by now:
This sort of sloppiness is not acceptable. User Gibsons has been penalized with a loss of 75 posting credits. Please, this is a serious forum, and we ask people to use very technical sounding language. THIS IS NOT OT!
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forrestroche
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Born2bwire
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No, but there exists the same amount of pressure on the liquid inside the straw as outside the straw. That is why it doesn't rise. There is no "gradient" in the pressure between the atmosphere outside of the pipe and inside it.
The straw-in-a-glass + vacuum is not necessary considering that there exists a gradient from water to air as there exists a gradient between the air and a vacuum. If you put a BFP in the air, you'd really throw the coriolis effect off, and the center of gravity of the earth. You wouldn't lose the atmosphere though.
you know in every space movie, if the hatch on a space shuttle opens or if there's a BFH (Hole) in the ship, it sucks everything out. why can't that happen with a BFP in the earth's atmosphere? What if the BFP diameter was .5 of earth's diameter?
Born2bwire
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To put it more correctly, "space doesn't suck, it blows." When there's a hole in a ship, stuff gets blown out into space because of the enormous difference in pressure between the exterior and interior of the ship. Nothing will get sucked out of your pipe because there exists no pressure difference between inside the pipe and outside it.
Generally, the velocity in a flow field is dependent on the pressure gradient. However, since it's a gradient and not strictly a pressure difference, the length scale is also important. The reason things get sucked out of a punctured pressure vessel (e.g. a spacecraft) very quickly is that the skin is thin, implying a large pressure gradient. The same pressure gradient exists from sea level to the edge of space as does within the spacecraft and without. The difference is that the length scale is the thickness of the atmosphere in the former case and the thickness of the hull in the latter. You can approximate the pressure gradient as the pressure difference from point A to point B divided by the distance between A and B.
If you want to look up the effects of diameter on the velocity field, Google Poiseuille's Law.
If you want to look up the effects of diameter on the velocity field, Google Poiseuille's Law.
Gibsons
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What if you built a very very tall wall arount the equator? same thing. Any force or mechanims you're imagining to get atmosphere out of the pipe would work equally well on the rest of the atmosphere. Think about why the entire atmosphere doesn't just blow off into space.
CycloWizards post explains it in more and better detail, though.
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