3975  Not just Rhythm, Synchrony now...

Date: Fri, 11 Nov 2005 09:35:19 -0500
From: seth <s1redh@GMAIL.COM>
Subject: Not just Rhythm, Synchrony now...

The following article appeared in this week's NY Times Science section. It
may be a scientific explanation of why sometimes a whole dance floor is kind
of swaying together.
All Together Now: Synchrony Explains Swaying By Kenneth Chang

What do pedestrians, some species of fireflies and pendulum clocks have in
common? Given half a chance, they act in unison, exhibiting what scientists
call synchrony. And that is what lay behind the unexpected swaying of the
Millennium Bridge in London five years ago, according to a new study.

This sleek $32 million footbridge, which stretches 1,050 feet over the
Thames, opened June 10, 2000, to great fanfare. But as thousands of people
streamed across, it began to wobble side to side, inducing queasiness and
fears that it might fall. Engineers saw that as the wobbling began,
pedestrians adjusted their gait to the wobbling motion. As more people
walked in lock step, the wobblier the bridge became.

Steven H. Strogatz of Cornell and his colleagues borrowed mathematics
describing the synchrony of fireflies and pendulums and applied them to the
dynamics of the bridge. The calculations, reported in the journal Nature,
show why the north section of the bridge remained steady with 150 people on
it but began swaying when the number exceeded 160.

Christian Huygens, a 17th-century Dutch physicist, first observed synchrony
in two pendulum clocks that hung close to each other. Even when he set the
pendulums in motion so they were not swinging in unison, they resynchronized
within half an hour.

Fireflies along rivers in Malaysia and Thailand also synchronize, thousands
flashing on and off at once.

As for the Millennium Bridge, after two years, an extra $9 million and the
addition of large shock absorbers, it no longer wobbles. (It was never in
danger of falling.)

Date: Fri, 11 Nov 2005 12:54:29 -0800
From: Igor Polk <ipolk@VIRTUAR.COM>
Subject: Not just Rhythm, Synchrony now...

Hardly possible to call it a "scientific explanation", it does not even
mention a word "resonance", but at least it gives a credible assurance (
since it was published in NY Times (!), not by some humble member of the
list ) that seemingly very complex phenomena can actually be explained by
scientific logic.

Igor Polk