RE: "Age of the Cybersaur" - Tail whipping

[Nathan Myhrvold <nathanm@MICROSOFT.com>]

Bullwhips crack because of a sonic boom, or shock wave caused by the tip of
the whip exceeding the speed of sound.   This has been documented since the
late 1950s when photographic techniques became good enough to capture the
tip of the whip.   Most whips measured achieve about Mach 2 - twice the
speed of sound.

I recently found the following student project on the net - it documents
that snapping a towel (as often occurs in locker rooms) is actually
supersonic as well.

http://www.pacsci.org/public/education/gallery/high_speed_photos/towel.html

It is only a little over Mach 1, so the sound is not as sharp as a Mach 2
bullwhip, but the principle is the same.

Our research (done with Phil Currie) showed that it is physically feasible
that the diplodocid sauropods used their tails like bullwhips, with the tips
going faster than sound.   This was possible without putting unusual
stresses on the tail, and without requiring unusual amounts of energy.  We
have a strong but circumstantial case that it is biomechanically possible,
but since a behavior does not fossilize directly one can't actually prove
that the diplodocids did this.

Nathan