Erik Reuter wrote:
>
> On Sun, Jul 06, 2003 at 07:36:53PM -0400, David Hobby wrote:
>
> > The formula above seems to be assuming that pressure at the axis
> > is zero, which is unrealistic.
>
> Actually, having a pressure near 1 atmosphere at the center is
> unrealistic. There is nothing to provide such a pressure. The pressure
> should be very low at the center. It won't be exactly zero, but the
> formula I gave is just an approximation.
Sure there is something to provide the pressure! The habitat
won't let air out, and you've pumped it up to the point where there
is 1 atm at the rim. Or?
>
> > At a guess, I would say that the air pressure throughout the habitat
> > will be pretty much the same. And it will be at whatever value the
> > habitat is PRESSURIZED to.
>
> Bad guess. There will be a pressure gradient from the center to the
> edge. The question specified it was pressurized to about 1 atmosphere
> at the rim. The pressure falls off from there as you move towards the
> center.
But look, here's a quote from the original question:
At 5.5 km (18,000 feet), atmospheric pressure is about 0.5 bar.
This is for Earth, and sounds about right. So even for
Earth, you get a pressure of .5 atm at around 5 km high for a
"surface" pressure of 1 atm. But the gradient will be weaker in
the habitat, for the two reasons I mentioned in my previous post:
1) Weight falls off closer to the axis.
2) The region of space "above" a given square on the "surface" is
wedge-shaped instead of box-shaped, tapering as it goes "up".
---David
Appeal to Authority: Rama had air at the axis, and Clarke
was usually good on physics.
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