Robert Cohen sent me an e-mail off-list asking some questions about my
recent post in which I mentioned the bicycle wheel held by a person on a
platform that can rotate. He questioned my analysis because I mentioned a
new momentum pointing in the vertical direction, and I implied it occurred
without an external torque.
He is correct, and I used that example badly. I did mention that it was not
the same as the gymnast problem. If, so then why did I write it? I threw
it into the discussion mostly because I wanted to say that angular momentum
physics can sometimes appear pretty bizarre. Most people would not predict
that twisting the spinning wheel would result in a new rotation about the
person's vertical axis. Of course, simply playing around with any rotating
object or gyroscope yields all kinds of seemingly strange results. Indeed,
if some of the Olympic maneuvers did not seem bizarre, we wouldn't be having
this discussion. So perhaps my post was totally superfluous... we already
agree things are happening which appear strange and are difficult to
analyze. And I have to admit that thinking through this logically is
requiring more time than I have, so I'd better be careful not to say more
things that seem "obvious" to me without thinking them through more
completely.
Michael D. Edmiston, Ph.D. Phone/voice-mail: 419-358-3270
Professor of Chemistry & Physics FAX: 419-358-3323
Chairman, Science Department E-Mail edmiston@bluffton.edu
Bluffton College
280 West College Avenue
Bluffton, OH 45817