Yes, all the streamlines are circular in the CM frame. But in the lab
frame the CM has a forward momentum. Compare with a forward travelling,
spinning frisbee (or football).
Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net http://www.velocity.net/~trebor
----- Original Message -----
From: "William Beaty" <billb@ESKIMO.COM>
To: <PHYS-L@lists.nau.edu>
Sent: Tuesday, July 23, 2002 4:56 AM
Subject: smoke-ring paradox
| Here's a trick question.
|
| When launching a ring-vortex, the "launcher" experiences a "kick," and
| when the moving vortex strikes a target, it can knock it over. Clearly
| the launcher injects momentum into the ring-vortex, and the vortex can
| deliver momentum into a target. However, continuity tells us that all
the
| streamlines are circular. Therefore, as the vortex progresses, no net
| volume of fluid builds up anywhere, and for every parcel of air which
| moves forward, there MUST another one moving backward.
|
| So, how can a ring-vortex carry any net momentum?
|
| :)
|
|
|
| (Note: ring-vortices and vortex-pairs DO transfer momentum, so that's
not
| where the trickery lies.)
|
|
|
| (((((((((((((((((( ( ( ( ( (O) ) ) ) ) )))))))))))))))))))
| William J. Beaty SCIENCE HOBBYIST website
| billb@eskimo.com http://amasci.com
| EE/programmer/sci-exhibits amateur science, hobby projects, sci fair
| Seattle, WA 206-789-0775 unusual phenomena, tesla coils, weird sci
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