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Topic: Air in Hole Through Earth (Read 8060 times) |
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SWF
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Air in Hole Through Earth
« on: Dec 17th, 2003, 7:39pm » |
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A hole is drilled through the center of earth such that the atmosphere flows to the earth's center. What must the diameter of the hole be in order for essentially all of the earth's atmosphere to be in the hole?
I know this involves some dull calculation, but the answer should be surprising. The main thing to take into account is (hint): pressure varies with distance from center of earth.
Obviously, many unrealistic assumptions can be involved in this one. To simplify the problem and give a common ground for everyone, use standard physics problem assumptions and the following: Through the use of an elaborate climate control system, the inside of the hole is held at a habitable temperature of 300K. The ideal gas law applies with gas constant such that: Pressure= Density * 86100 N-m/kg (about right for air at 300K). "Essentially" all of the atmosphere in the hole means the pressure at sea level is one-millionth of normal atmospheric pressure of 1e5 N/m2 (it can't really reach zero).
Earth has uniform density = 5517 kg/m3;
Universal gravitation constant G=6.673e-11 N-m2/kg2;
Radius of earth = 6.37e6 m;
Mass of earth's atmosphere = 5.1e18 kg.
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Eigenray
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Re: Air in Hole Through Earth
« Reply #1 on: Dec 17th, 2003, 8:42pm » |
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Sweet merciful crap! 3.8e-70m!
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| « Last Edit: Dec 17th, 2003, 10:37pm by Eigenray » |
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Eigenray
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Re: Air in Hole Through Earth
« Reply #2 on: Dec 17th, 2003, 11:30pm » |
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Assuming a linear temperature change from T=6000K at the center to T=300K at the surface, I get an answer of about 83 Angstrom, which is much more reasonable.
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| « Last Edit: Dec 17th, 2003, 11:39pm by Eigenray » |
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SWF
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Re: Air in Hole Through Earth
« Reply #3 on: Jan 12th, 2004, 8:19pm » |
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Excellent, Eigenray. Your first answer is the same thing I get for the diameter of the hole, although I haven't tried the linear temperature variation, since I want the hole to be habitable. However, being less than 1e-50 times the diameter of an electron means this hole would be difficult to climb into.
The important point to remember is: be careful when making deep holes in the earth or the surface will run out air.
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Speaker
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Re: Air in Hole Through Earth
« Reply #4 on: Jan 12th, 2004, 8:30pm » |
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That is an incredible fun fact. I just have to find some way to work it into polite conversation.
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They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety. <Ben Franklin>
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Eigenray
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Re: Air in Hole Through Earth
« Reply #5 on: Jan 12th, 2004, 11:14pm » |
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on Jan 12th, 2004, 8:19pm, SWF wrote:| Excellent, Eigenray. Your first answer is the same thing I get for the diameter of the hole |
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Oh good. I had to correct it twice cause I kept losing constants.
Quote:The important point to remember is: be careful when making deep holes in the earth or the surface will run out air.
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Words to live by.
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John_Gaughan
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Re: Air in Hole Through Earth
« Reply #6 on: Jan 14th, 2004, 8:06am » |
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on Jan 12th, 2004, 8:19pm, SWF wrote:| The important point to remember is: be careful when making deep holes in the earth or the surface will run out air. |
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Given the thickness of the Earth's crust and the feasibility of drilling into the mantle, I am more concerned about magma pouring out of the mantle than air pouring in.
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Sameer
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Re: Air in Hole Through Earth
« Reply #7 on: Feb 2nd, 2004, 12:41pm » |
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Assuming there was no earthly distortion until man arrived and a footstep by a very heavy person caused total annihilation!!! I wonder if this made dinosaurs extint!!
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"Obvious" is the most dangerous word in mathematics.
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John_Gaughan
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Re: Air in Hole Through Earth
« Reply #8 on: Feb 2nd, 2004, 9:57pm » |
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on Feb 2nd, 2004, 12:41pm, Sameer wrote:| Assuming there was no earthly distortion until man arrived and a footstep by a very heavy person caused total annihilation!!! I wonder if this made dinosaurs extint!! |
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Smoking caused the dinosaur extinction. Everyone knows that!
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fil
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Re: Air in Hole Through Earth
« Reply #9 on: Apr 24th, 2004, 8:13pm » |
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Just stumbled across this discussion, and I'm deffinately lost with yaalls equations.
Are you saying that a small hole drilled through the earth would require more air to fill it than the atmosphere has to provide?
Kindly,
Fil
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SWF
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Re: Air in Hole Through Earth
« Reply #10 on: Apr 27th, 2004, 7:31pm » |
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on Apr 24th, 2004, 8:13pm, fil wrote:| Are you saying that a small hole drilled through the earth would require more air to fill it than the atmosphere has to provide? |
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Yes, but only under the unrealistic assumptions stipulated by the problem. Using the Ideal Gas Law, means doubling the pressure of the gas doubles the density. The increase in density allows more gas fit in the hole, which further raises the pressure and density.
It turns out pressure as a functions of distance from center of earth, r, is something like
P0*exp(C*(R*R-r*r))
where R is radius of earth and P0 the pressure at earth's surface. C is a constant involving G, density of earth, T, [pi], R, and temperature.
Eventually pressure computed from Ideal Gas Law reaches a level where the substance assumed to be a gas, has a higher density than any normal solid. Well before that point, the approximation of density doubling with a doubling in pressure is incorrect.
I haven't tried to figure out how big the hole would need to be to consume the atmosphere assuming some maximum permissible density.
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| « Last Edit: Apr 27th, 2004, 7:32pm by SWF » |
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