From: Adrian Tymes (wingcat@pacbell.net)
Date: Fri Feb 28 2003 - 18:20:45 MST
--- spike66 <spike66@attbi.com> wrote:
> Adrian Tymes wrote:
> >>one is sitting on a swivel chair and by thrusting
> >>one's arm in specific directions, one can make the
> chair turns.
> >
> > It's called "friction"...Meanwhile, all you
> perceive
> > is yourself spinning.
>
> One can turn oneself in a swivel chair even if the
> swivel bearings are perfectly frictionless. Granted
> you cannot get your self spinning, but you can turn
> yourself around. It is difficult to describe the
> motions, but it can be done.
The friction I described was not WRT the swivel chair
itself, but WRT the ground. Though, giving the right
bearings friction could serve the same purpose. (Of
course, certain other bearings would not help. Which
is which is left as an exercise to the reader; one
hint: if it looks like adding friction to the bearing
you're thinking of would prevent what I suggest,
that's not the bearing I mean.)
> >>It is the same
> >>effect that happens when a cat falls down and
> lands
> >>on its feet - by twisting its torso.
> >
> > Twist to get at least one paw on the floor, while
> the
> > rest of the body twists the other way...
>
> The cat stretches her front paws and pulls in her
> rear paws, twists her body. The rear half turns
> more than the front half, since it has a smaller
> moment of inertia. Then she stretches out her
> rear paws and pulls in the front, twists back the
> other way. Now the front turns more than the rear.
> Repeat process. The cat can turn herself around
> in freespace without touching the floor and without
> violating any conservation of angular momentum laws.
Problem: conservation of angular momentum when
stretching out or pulling in the paws of the
(spinning) front or rear half. Angular momentum is
conserved across that action too, so as to conserve
the angular momentum of the whole feline, even if that
means merely pulling in or stretching out the paws
causes a change in rotation speed of that half of the
cat. Ask any ice skater about pulling in arms while
spinning to spin faster, even without applying any
other torque.
All forces are always in effect, so for all actions,
compute their effect on all forces. Most seeming
loopholes in momentum result from failure to account
for the effect of some action on some force, but
reality never makes this oversight.
> >>This new paper deals with the same idea and
> involves
> >>with a curved 4D
> >>spacetime. By stretching and retracting the
> "limbs"
> >>of a body, Wisdom
> >>showed that one can "swim" through a curved
> >>spacetime...
>
> This one stretches my imagination however. spike
As I posted, there exists a way to produce physically
measurable motion from this, given the rates
described. Perhaps not much (at least, without a
*lot* of costly precision engineering), but still
measurable; therefore, I must demand physical evidence
before believing. I can certainly imagine several
ways this could be true, though, but I know I can also
imagine the physically impossible.
This archive was generated by hypermail 2.1.5 : Fri Feb 28 2003 - 18:24:25 MST