-Z- (z@gundam.com)
Tue, 7 Nov 2000 22:14:06 -0800


> -----Original Message-----
> From: owner-gundam@1u.aeug.org [mailto:owner-gundam@1u.aeug.org]On
> Behalf Of Mark Wilson
> Sent: Tuesday, November 07, 2000 11:01
> To: gundam@aeug.org
> Subject: RE: [gundam] Gravity within a colony (was: Funnels and flying
> MS)
>
> BTW, A colony cylinder that has a 500m radius ( a 1 km diameter) would need
> to rotate as follows:
>
> earth g = 9.81 m/s^2 = colony g =w*r^2
>
> Solving for w, w= 9.81/(r^2) = 9.81/250000 = 3.924*10(-5) rad/s
>
> In more common terms, to convert rad to degrees, multiply rad by 180/Pi.
> Therefore, 3.924E-5 rad/s is 0.0022 degrees/s. or 0.1349 degrees per
> minute. Or, 2668 minutes per revolution, or one turn every 44.5 hours.
> Make the colony 250 m in diameter, and the rotation rate increases to:

G = 9.80665 m/s^2, so w = 0.0000392266 radians per second = 0.00224752 degrees
per second, but I follow your reasoning. But we're not concerned with the
angular acceleration, but rather with the effective Coriolis force and resultant
pseudogravity (gravity gradient).

The basic equation for describing the magnitude if the force is f=mv^2r, where f
us the Coriolis force, m is the mass, v^2 the angular velocity in degrees per
second and r the radius in feet (not meters) of the rotating module.

The rotational rates I cited weren't derived by me, but rather by the engineers
who did the comparative design study for the various configurations (cylinder,
sphere, and torus) for NASA (Space Settlements, NASA SP-413) in 1975 and, of
course, Gerard K. O'Neill's own figures for the Island One, Two, and Three
habitats described in High Frontier. These figures have been cited or
reiterated in every other reference I've ever seen and confirmed by a table of
rotational rates, derived using the formula cited above, in G. Harry Stine's
Living In Space (1997, M. Evans & Co., ISBN 0-87131-841-5).

> What about if you are at the axis of the colony, where the radius is zero,
> and you are pushed towards the outer wall? Well, the only way you would
> have motion is if something pushed you towards the wall. As you came
> closer to the spinning wall, you would have NO attraction to the wall. If
> there is an atmosphere, the air being dragged along with the cylinder wall
> would create a wind relative to you, which you slowly speed you up in the
> direction of the colony spin and pull you further out to the wall until you
> schmacked into it. Depending on how much drag you have, the air can speed
> you up tangentially a lot, causing you to smack nearly vertically into the
> wall as if you fell from a height. If there were no air in the colony, you
> would travel straight out to the wall, which to you would look like a huge
> moving wall. Depending on the colony size, it could be moving quite fast.
> Your impact would then be more like jumping out of a moving car than
> dropping from a height.

It's not the fall that kills you, it's the jolt when you land. That wall is
traveling at 644 kph (400 mph) and, no matter how gently you collide with it,
it's going to smack you silly.

"Whether the rock hits the pitcher or the pitcher hits the rock, it's going to
be bad for the pitcher!" --Sancho Panza, Don Quixote De La Mancha, Miguel
Cervantes.

> Yeah, I have a couple degrees in this stuff--I'm not making it up.

Which "stuff" is that? Physics? Ballistics? Orbital dynamics?

I myself am not so much a scientist as an engineer. My training is in
aeronautics and avionics, with particular emphasis on weapons control systems
mechanics.

> To the previous message:
>
> Being at the center of a mass does not crush you. At the center of the
> earth, assuming there was no heat, you would be experiencing gravity from
> all directions. Since the mass casing the gravitation would be around you,
> you would be PULLED in all directions, making you essentially weightless.
> The gravitational force ACTS through the center, but is not concentrated
> there. If you travel to the center of a splinting object, you would feel
> essentially no force. Try sitting on the edge and then the center of a
> merry-go-round to see what I mean.

You're assuming objects at rest in various points along a gravity gradient. I'm
talking about objects in motion within a rotating frame of reference.

Try walking, jumping or tossing a ball from the center to the edge, from edge to
edge, or around the edge, and you'll see what *I* mean.

-Z-

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