OT: Building O'Neill habitats on Earth?

--- In spacesettlers@yahoogroups.com, Ian Woollard
> On 7/19/05, Al Globus wrote:
> >
> > The forces in a colony are completely different.
>
> Why does everyone always assume that everything is always so very
different?

Why do you assume they are the same?

To put it bluntly, we will not know for sure until we go out there and
try out space settlements for a while.

We can guess, but so far we are only guessing.
>
> The laws of physics are the same in space as on the Earth.

Yes. But different laws apply there than here.

On earth, there is gravity. We do not know how to make a gravity
field. Space settlements will not have gravity. Rotating them will
produce something similar to gravity. But NOT the same.

> The pressure
> distribution of air relates to the laws of physics.
>
> On Earth, every molecule in the atmosphere feels the pull of Earth's
> > gravity. In the
> > colony, the attraction between the hull and each molecule in the
> > atmosphere is negligible.
>
> Strictly correct.
>
> The only force on a given atmospheric
> > molecule is the other molecules plus a shear force in a layer just
> > above the hull and around any other rotating hardware, but that force
> > is around the axis of the rotation, not towards the hull.
>
> Actually, no shear force, to a good approximation they're all moving
at the
> same speed over short distances, and the mean collision distance is
a short
> distance.
>
> No, you're forgetting about momentum; they're all moving relative to
the
> axis; rotating around it.
>
> I the Lucio
> > is right. The pressure and density will probably be uniform, with the
> > shear forces causing the atmosphere to rotate around with the hull.
>
> Yup. Viscosity means that the atmosphere rotates at the same rate
the hull
> does.
>
> There is no reason that I can think of to believe that the pressure at
> > the hull will be any different than the center.
>
> You're in a non inertial reference frame. So there is an apparent
> centrifugal force that presses outwards from the central axis with a
force
> of mrw^2 where m is the mass, r is the distance from the axis, and w
is the
> angular speed in radians per second. Of course from the point of
view of a
> fixed external reference frame it's really momentum.
>
> Anyway, the momentum, centrifugal force/effect presses on the air as
well,
> and tends to compress it out to the rim. You can work out the pressure
> distribution. It's a bit like stirring your cup of coffee, except
the cup is
> rotating with the coffee. The pressure of the coffee is higher at
the rim
> than the center (greater head).
>
> Larry Niven pointed out in his Ring Worlds books, that with big enough
> habitats you don't need the endcaps, only walls a few hundred
kilometers