 |
 |
||||
|
|
||||
Mark Wilson (mmwilson2@earthlink.net)
Wed, 8 Nov 2000 6:31:9 -0500
> [Original Message]
> From: -Z- <z@gundam.com>
> To: <gundam@aeug.org>
> Date: 11/8/00 1:14:19 AM
> Subject: RE: [gundam] Gravity within a colony (was: Funnels and flying MS)
>
> > -----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).
Uhm, if you don't understand the physics, then maybe you should look this
up. There is no gravity generated by merely spinning a body. Gravity
refers to a specific type of force; a "gravity gradient can only truly
occur when there is really gravity present.
Centripedal acceleration is not angular acceleration. Even if the rotation
rate is constant, there is centripedal acceleration (think about his--even
when the merry-go-round isn't accelerating, you still have to hold on to
avoid being flung off).
> 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 dimensions for force are mass*length/(time^2). Degrees are not units
you can multiply by without conversions. Your equation above gives:
f=mv^2r. According to you, the dimensions for force are
mass*(length/time)^2*deg/s.
With all due respect, I think I'll go with Isaac Newton's version, not
yours.
Also, the "Coriolis" effect is measured tangential to the circle, not
perpendicular. We are interested in the forces perpendicular to the circle
edge.
> 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 tor us) 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).
>
Look, you really don't seem to have a grasp on the physics here. Quoting a
study doesn't really matter if you don't understand the basics.
> > 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.
These numbers again are way too high.
> > Yeah, I have a couple degrees in this stuff--I'm not making it up.
>
> Which "stuff" is that? Physics? Ballistics? Orbital dynamics?
Well, lets see--I have two engineering degrees, including a graduate
degree, and I've taught engineering at a major U.S. University.
That said, the forces and kinematics of a spinning body have nothing to do
with "ballistics" (sorry, I don't think they offer degrees in that one!) or
orbital dynamics. This is first year physics or second year dynamics for
ANY engineering student.
> 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.
I would NEVER tell you how to turn a wrench on a system I didn't design;
please leave the physics to those who understand it. There is way too much
pseudo-science on this group to begin with.
> > 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 spinning 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.
Huh? Uh, so was I. A large spinning body at a LaGrange point would not
have any gravity other than the basic gravity generated by a large object.
So, no, I wasn't assuming a "gravity gradient". Try sitting on a
merry-go-round, and for the same rotation rate, what is harder to hold on
to? The center or the edge? Even my kids have figured that one out;)!
In other words, there is no gravity involved at all in a spinning space
colony cylinder. The act of spinning does not create gravity. It creates
a reaction force on a body due to centripedal acceleration; this force
sticks you to the outside of the cylinder and APPEARS like gravity, but
isn't. Again, ride a merry-go-round...
> 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.
It will travel in a straight line ballistic path based on your release
point--so what?
> -Z-
>
>
> -
> Gundam Mailing List Archives are available at http://gundam.aeug.org/
Mark Wilson
-
Gundam Mailing List Archives are available at http://gundam.aeug.org/
This archive was generated by hypermail 2.0b3 on Wed Nov 08 2000 - 20:17:40 JST