halle1@houxz.UUCP (J.HALLE) (08/14/84)
Scientific American had an article a couple (a few?) years ago about just this phenomenon. (Divers spinning in apparent violation of L conservation.) I suggest anyone interested read the article.
matt@oddjob.UChicago.UUCP (Matt Crawford) (08/15/84)
Actually, you are talking about the law of conservation of ANGULAR
momentum, angular momentum being conserved separately from linear
momentum. Here is an experiment you can try to demonstrate to your-
self what is happening to cats and divers when they are falling:
Take a wheel from a bicycle and attach some sort of axle by
which you can hold it. Now sit in a reasonably well-lubricated
swivel chair, holding the wheel's axis vertical. Now grab a
spoke and give the wheel a spin. You will begin to turn in the
other direction.
If you can't manage the bike whhel, do this instead: sit back
in the swivel chair with your legs up and with a heavy book in
your hands. (I am using Misner, Thorne and Wheeler's GRAVITA-
TION.) Slowly hold the book out to one side, then smoothly
swing it in front of you and around to the other side. Bring it
back in to your lap and extend it out to the original side
again. Repeat until enlightenment is acheived.
All the while, your total angular momentum is zero (ignoring
friction), yet the angle your are facing changes. If you want to
get some net angular momentum you can hold the book out and fling it
to one side, with a velocity perpendicular to the direction from you
to it. (This will hurt your shoulder, I think.)
___________________________________________________________
Matt University ARPA: crawford@anl-mcs.arpa
Crawford of Chicago UUCP: ihnp4!oddjob!mattmartin@ism780.UUCP (08/17/84)
#R:heurikon:-26800:ism780:20300007:000:491 ism780!martin Aug 16 12:46:00 1984 This is simple. In those tents they had set up on the pool deck, there was an anti-diver for each diver in the competition. Now, suppose Greg Luganis does a reverse somersault with one and a half twists. Precisely at the time he is supposed to twist, the anti-Greg Luganis in the tent below twists in the opposite direction, thereby instantaneously causing Greg Luganis to twist correctly. This follows directly from the law of Consevation of Spin. martin smith, INTERACTIVE, Systems
jeff@heurikon.UUCP (08/19/84)
While watching the Olympic diving competition, I was impressed
with the divers' ability to spin while doing somersaults.
I always thought they had to impart their spin energy by
pushing off just right and then use their limbs to control
the spin rate, like an ice skater. However, I viewed a lot
of slow motion of the dives and noticed that the divers
started their spins while airborne and then were able to stop
their spinning motion completely prior to hitting the water.
How could they do this? They don't have wings. Where does
the angular momentum come from that started the spins, and
where does it go to stop? Can they convert their initial
tumbling motion back and forth to spinning motion?
Please post responses. Thanks.
--
/"""\ Jeffrey Mattox, Heurikon Corp, Madison, WI
|O.O| {harpo, hao, philabs}!seismo!uwvax!heurikon!jeff (news & mail)
\_=_/ ihnp4!heurikon!jeff (mail - fast)