Re: The Olympics

[Larry Cartwright <exit60@IA4U.NET>]

Interesting how the some of the same questions keep coming up from time
to time.  From the PHYS-L ARCHIVES at
<http://mailgate.nau.edu/archives/phys-l.html>:

On Mon, 21 Dec 1998, Herb Schulz wrote:

"It is possible to rotate your body to face a different direction
without violating angular momentum conservation.  The trick is to
realize that angular momentum is a vector law and that you can divide
your body into two sub-bodies that can rotate "against" each other.
By changing the moment of inertia of the upper and lower parts of the
body appropriately you can have DIFFERENT and opposite angular
velocities so the different parts of the body will rotate through
different angles in the same amount of time. Change the relative I's
and go the other way and the body is now facing a different direction."

"That's how we aim camera's at different points in space without using
fuel 'jets'!  Spin an internal body one way and the rest of the
satellite rotates the other way."

Best wishes,

Larry
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Larry Cartwright  <exit60@ia4u.net>
Physics and Physical Science Teacher
Charlotte HS, Charlotte MI USA
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

On 24 September 2000 Justin Parke wrote:
> Perhaps the answer to this question should be obvious to me, but after
> pondering for a while have not been able to answer it.
>
> It seems that the divers in the olympics (and the "trampoliners") are able to
> execute  half-twists, beginning and ending the twist in mid-air.  I do not
> know how they do this without violating conservation of angular momentum.
> Could someone enlighten me?