Copyright 2003, all rights reserved
Lizard hair, tie-dye vitamins, hottest spot on Earth
How does a gecko lizard cling upside down and scoot across something slick, like
glass? —Shirley, Panama City, Florida
A lizard's (Tokay gecko) hairy foot, clinging to glass [Kellar
Autumn, Lewis & Clark College, Portland, Oregon]
A: Hair, geometry, and intermolecular force do the trick, says Kellar Autumn,
biology professor at Lewis and Clark College and the man who cracked the gecko’s
secret. Five hundred thousand tiny hairs blanket the sole of the lizard’s foot.
Each hair tip splits into hundreds more and each of those is shaped like a
spatula. A wee spatula too small to see with the best optical microscope. Its
diameter is less than the wavelength of visible light.
Such microscopic hairs can pry into practically any surface for purchase. At
gecko-hair scale, the smoothest glass appears bumpy and pitted. However, the
gecko does not use the friction between her foot and the micro pits to stick.
Her way is subtler and more powerful.
Instead, she capitalizes on the transient electrical forces between her hair
molecules and the molecules of whatever surface she scampers across. She places
her foot "palm" first, uncurls each toe like a party favor, sticks each spatula
hair into the glass skylight, pushes the spatula flat, and gets the hair
molecules so close to the glass molecules that they electrically bond for an
instant. The sticking power is 600 times greater than friction.
The temporary bond, due to van der Waals attraction, depends on the shifting
dance of electrons about the nucleus. Consider two jammed-together molecules. At
any given instant, the electron cloud about a molecule in the gecko’s foot will
be more piled up on one side than the other and therefore more negative than
usual on that side. The negative charge pushes the electrons in the nearby glass
molecule away to its other side and the opposite charges attract each other
briefly. This condition oscillates back and forth (resonates), causing the two
molecules (foot and glass) to stick together.
She unzips her feet like tape from a ceiling 15 times per second, peeling off
and curling up each toe like a party favor coming back to normal. She simply
lifts the flattened spatula hair by restoring the angle that the hair shaft
makes with the glass to 30 degrees and the hair pops off. That’s geometry.
By the way, Andre K. Geim of the University of Manchester has imitated the
gecko’s adhesive and produced one square centimeter of "gecko" tape. When we
make enough to cover your hand (200 sq cm)—you can suspend your 90-pound (41 kg)
body (sorry, that’s all) from a pane of glass with that one hand.
Someday, a swarm of "geckobots" may climb a burning building searching for
survivors or explore Martian cliffs," says Autumn.
How geckos stick to walls
Scientific American: Gecko inspired adhesive
What does a vitamin look like? When asked this question, the best I could think
of was to write you. —David, Albuquerque, New Mexico
Vitamin E [©1995-2003 by Michael W. Davidson and the Florida State
University, used with permission]
A: Beautiful and bizarre. Vitamins are organic molecules (i.e., made of
carbon compounds) that form crystals big enough for a digital optical microscope
to capture their gaudy structure. Vitamin C looks like wild feathery fans of
blue, red, and yellow. Vitamin E appears as a bursting sunflower sending out
rays of blue and gold. Vitamin H (biotin) looks like a symmetrical design of
The crystals interact with polarized white light to make "a beautiful
kaleidoscopic spectrum of color," says Michael W. Davidson of the National High
Magnetic Field Laboratory.
Michael W. Davidson, Florida State University: The vitamin photo gallery
Q: Where is the hottest place on Earth? I'm
guessing it's somewhere like the Sahara. What, if any, humans live there and how
do they eke out a living? —Tinjoy, Cebu,
A: The hottest spot is Al-‘Aziziyah, a small town in Libya, a few miles south
of Tripoli. On Sep. 13, 1922, here the temperature soared to 136 degrees F (58
degrees C)—the highest ever recorded on Earth.
Libya---the hot spot [Map courtesy of www.theodora.com/maps used with
Strangely enough, people do eke out a good living in this North African town
a few miles south of the Mediterranean Sea. It is a major trade center of the
Al-Jifarah plain, about 200 miles (300 km) north of the Sahara. What’s more, the
gray-brown soils of the Al-Jifarah Plain are fertile, though salty from over
Most hot places are in deserts (as you guessed) and low land, like Death
Valley, California—the second hottest spot and the lowest place (-178 feet, -54
m) in the Western Hemisphere. On July 10, 1913, Death Valley recorded a high of
134 degrees (57 degrees C).
A lowland is hotter because air warms as it descends just as air cools as it
Less than 100 miles west of the Red Sea, nestled in the Danakil Plain, lies
Dakol in northeastern Ethiopia. This place suffers the world’s highest
year-round average temperature—94 degrees F (34 degrees C), with zooming highs
of 125 degrees F (52 degrees C). The flat, barren African plain—broken by an
occasional volcanic cone— stretches like a widening funnel to the sea. The plain
drops at places to 380 feet below sea level. Sometimes no rain falls during a
year. The parched soil is too poor to farm.
An African desert at sunset [Corel]
few who live here—the Danakil— make a
living prying loose slabs of solid salt from the plain’s salt pans. Others herd
sheep, goats, cattle, and camels over the lonely steppes.
USA Today weather: Highs
Theodora: maps and flags
Theodora and CIA World Fact Book: Libya
(Answered July 25, 2003)