Flag-flapping
poses one of "the essential difficulties of the general
problem of elastohydrodynamics" -- the study of deformable
bodies in air or liquid flow, observes physicist Greg
Huber of the University of Massachusetts at Boston. The
guru of flag-flapping research is Jun Zhang of New York
University. Because of the complexity of three-dimensional
simulations of flapping flags, he and his colleagues at
NYU and Rockefeller University are simulating how a simplified,
one- dimensional "flag" -- actually a silk thread
floating atop a soapy film -- "flaps" when exposed
to mild currents.
So far, their work has shed some light on the question:
The threads generate vortices (like little tornadoes)
that may play a role in causing windblown flags to repeatedly
lose their stiffness and partly furl up -- that is, to
flap. Although the experiment looks simple, flag-flapping
"is one of the most complex phenomena in hydrodynamics,"
Zhang has admitted.
Or consider a coffee stain: Why, as it dries, does it
form a ring? Considering that scientists have explored
the moon, cured epidemic diseases, tapped nuclear energy
and created "baby pictures" of the primordial
cosmos, surely they have explained coffee rings. No! An
answer didn't arrive until 1997, after much head- scratching
by physicists.
Even that answer, which involves complex interactions
between the liquid and subtle irregularities on a table
surface, is incomplete: Certain aspects of the problem
involve phenomena "that people don't understand very
well, where the liquid and solid and air are in contact
together," Huber says.
"You'd think those would be things people had solved
in the past, but they remain mysterious," acknowledged
Huber, who is co-author of a paper on coffee rings and
has written about flag-flapping.
Indeed, science has explained so much that it's easy to
forget how much it hasn't. Scientists still fight over
muscle motion, meteorites and the reliability of fingerprinting.
Every elementary-school encyclopedia cites Luigi Galvani,
the Italian scientist who made frogs' legs jump by exposing
them to electrical sparks, for revealing the electrical
basis of muscle motion.
Or had he? More than two centuries later, we still don't
have a complete explanation. |
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Strange
But True
Q: A fiery meteor streaks through the Earth's
atmosphere, glowing incandescent, and thuds down
loudly in your front yard. Could you grill a hamburger
on it?
A: It's a common misconception that meteors are
hot, says Bob Berman in "Secrets of the Night
Sky." In August 1991, when one hit on a front
lawn in Noblesville, Ind., two boys close by were
able to touch it immediately. "The icy lower
atmosphere deep- freezes the stone so that it's
only slightly warm by the time it reaches the
ground."
Q: Insomnia is common enough. Have you ever lost
sleep over pseudoinsomnia?
A: Some people will think they're not getting
a good night's rest, but sleep lab tests show
they're sleeping just fine. One hypothesis, reports
Josh Gerow in "Psychology: An Introduction,"
is that such sleepers dream of lying awake and
trying to get to sleep, and in the morning remember
these dreams and conclude it was a fretful, sleepless
night. Usually just finding out that they're sleeping
normally is enough to cure their pseudoinsomnia.
Q: Copycat crimes have made the news. Are there
copycat acts of kindness?
A: When researchers staged a roadway situation
in which a woman needed help changing a tire,
only 35 of 2,000 passing motorists stopped, says
Dennis Coon in "Introduction to Psychology."
But when a second flat-tire scene was staged a
mile before the test car, with the woman getting
help, 58 drivers stopped down the road. Presumably
some of these were copycat good Samaritans.
Why some people lend a hand and others don't is
a hot area of study, but generally those who feel
good tend to do good, even when their moods are
artificially induced, as by having just found
a quarter or heard good news on the radio.
"We are, in truth, more than half what we
are by imitation," Lord Chesterton said.
"The great point is, to choose good models
and to study them with care."
Q: A great party trick: Print CARBON in red, DIOXIDE
in blue, then have guests peer at the words through
the long stem of a wine glass held over the paper.
Notice that CARBON appears inverted but not DIOXIDE.
How can this be?
A: Remind your audience that a prism breaks down
sunlight into a rainbow of colors. So maybe the
lens-like stem acts differently on the red and
blue wavelengths? But that seems incredible. De-mystification
occurs when you view CARBON DIOXIDE through the
back of the paper turned upside down. It has nothing
to do with the two colors. Both words were inverted,
but this is masked because DIOXIDE is symmetrical
about a horizontal midline.
Send questions for brothers Bill and Rich to strangetrue@compuserve.com.
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