Re: The Olympics

[Mark Sylvester <msylvest@XNET.IT>]

At 05:50 25/09/00 , you wrote:
> > It seems to ME that a stranded, motionless astronaut should be able
> > to do an 'about-face' maneuver in empty space, ending up motionless,
> > but facing 180 degrees from the original direction. (without
> > violating any basic principles!)
>
> If you mean rotating the entire body by 180 degrees (or any amount) it
> seems to ME that this is the rotational equivalent to displacing your
> body by some amount in empty space.  Just as an astronaut can propel one
> part of his/her body forward while propeling the rest backward, so s/he
> can twist the head around and have the rest rotate oppositely.  I don't
> see how to generate a net displacement or rotation.


The difference between the translational and rotational cases is that you
can change the moments of inertia of the upper and lower parts of the body
by extending and retracting arms and legs. So extend arms, retract legs....
twist upper body right, lower body left....  retract arms, extend
legs....  twist upper body left, lower body right. You end up with a net
rotation. I've seen strobe photographs somewhere of a cat doing this.

Mark



> \_/^\_/^\_/^\_/^\_/^\_/^\_/^\_/^\_/^\_/^\_/^\_/^\_/^\
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> Doug Craigen
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Mark Sylvester
United World College of the Adriatic
Duino TS Italy
+39 040 3739 255