Arquímedes, 22 siglos más tarde, sigue vigente
Por Kenneth
Chang, The New York Times
Por última vez: Arquímedes no inventó un rayo de la muerte.
Sin embargo, más de 2.200 años después de su muerte, sus
inventos siguen impulsando la innovación tecnológica –a tal grado que expertos
de todo el mundo se reunieron hace poco para una conferencia sobre su
perdurable influencia, en la Universidad de Nueva York.
La leyenda del rayo de la muerte cuenta que Arquímedes usó
espejos para concentrar luz solar e incinerar barcos romanos que atacaban su
hogar, Siracusa, la antigua ciudad Estado de Sicilia. Se ha demostrado su
falsedad al menos tres veces en el programa de televisión “MythBusters”.
En lugar de ello, es un aparato mundano atribuido al gran
matemático, inventor, ingeniero y planeador militar griego –el tornillo de
Arquímedes, una espiral adentro de un cilindro- el que tiene un nuevo uso en el
siglo XXI. Durante miles de años, los agricultores han usado esta sencilla
máquina para el riego: colocada a cierto ángulo con un extremo sumergido en un
río o lago, se la da vuelta al tornillo con una manivela, lo que hace que el
agua suba y salga al otro extremo.
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Chris Elliott/Western Renewable Energy. For this hydropower generator at Dartmoor National Park in Devon, England, water flows in at the top and turns the Archimedes screw.
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Hace un par de décadas, los ingenieros descubrieron que
operar un tornillo de Arquímedes al revés –es decir, dejar caer agua en la
parte superior haciendo que el tornillo gire al tiempo que el agua baja al
fondo- es una forma sólida, económica
eficaz de generar electricidad con el agua de arroyos pequeños. La
producción de energía es modesta, suficiente para una aldea, pero con poco
impacto sobre el medio ambiente. A diferencia de las cuchillas de las turbinas
que girar en enormes plantes de energía hidroeléctrica, un tornillo de
Arquímedes permite que los peces naden a través de él. Un generador de este
tipo fue comisionado por la reina Isabel II de Inglaterra para suministrarle energía al Castillo de
Windsor; el primero en EE.UU. podría comenzar a operar el año próximo.
“Sembró las semillas para tantas ideas originales que
pudieron crecer a través de las eras”; afirmó Chris Rorres, profesor emérito de
matemáticas en la Universidad Drexel, en Filadelfia, quien organizó la
conferencia.
Sólo sobrevive un puñado de escritos de Arquímedes, y mucho
de lo que pensamos que sabemos sobre él fue escrito siglos después de su
muerte. Algunas de las conferencias del evento propusieron usar la inventiva
actual para tratar de descubrir lo que realmente logró Arquímedes en la
antigüedad.
Arquímedes supervisó las defensas de Siracusa, y aunque lo
espejos del rayo de la muerte y los cañones de vapor (otro presunto invento de
Arquímedes) eran demasiado fantásticos, la garra de Arquímedes parece haber
sido un arma real usada contra la fuerza naval romana.
“Arquímedes conocía la estabilidad de este tipo de barco”,
aseguró Harry G. Harris, profesor emérito de ingeniería estructural en Drexel y
quien ha construido un modelo de la garra. “Cuando se mueve rápido a través del
agua es estable. Al estar inmóvil o avanzar muy lentamente, es muy fácil de
volcar”.
Así que al usar un principio de Arquímedes –la ley de la
palanca, que hace posible que una fuerza pequeña levante un gran peso, como en
los subibajas y poleas- una garra al final de una cadena sería bajada y engancharía
un barco romano, para luego ser levantada, volcando al barco y estrellándolo
contra las rocas.
“Conjeturó las leyes fundamentales de la naturaleza, las
demostró matemáticamente y entonces fue capaz de aplicarlas” dijo Rorres sobre
Arquímedes.
Publicado
en “The New York Times International Weekly” en colaboración con Clarín el
24/AGO/2013
EL VIDEO DE LA CONSTRUCCIÓN DE LA "MINI-CENTRAL"
DE LA FOTO:
Un video explicativo sobre el tornillo de Arquímedes en:
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| Fuente: hidrometalica.com |
NOTA ORIGINAL EN INGLÉS:
Archimedes:
Separating Myth From Science
By KENNETH
CHANG - Published: June 24, 2013
For the
last time: Archimedes did not invent a death ray.
But more
than 2,200 years after his death, his inventions are still driving
technological innovations — so much so that experts from around the world
gathered recently for a conference at New York University on his continuing
influence.
The death
ray legend has Archimedes using mirrors to concentrate sunlight to incinerate
Roman ships attacking his home of Syracuse, the ancient city-state in the
southeast Sicily. It has been debunked no fewer than three times on the television
show “Mythbusters” (the third time at the behest of President Obama).
Rather, it
is a mundane contraption attributed to the great Greek mathematician, inventor,
engineer and military planner — the Archimedes screw, a corkscrew inside a
cylinder — that has a new use in the 21st century. For thousands of years,
farmers have used this simple machine for irrigation: Placed at an angle with
one end submerged in a river or a lake, the screw is turned by a handle,
lifting water upward and out at the other end.
A couple of
decades ago, engineers found that running an Archimedes screw backward — that
is, dropping water in at the top, causing the screw to turn as the water falls
to the bottom — is a robust, economical and efficient way to generate electricity
from small streams. The power output is modest, enough for a village, but with
a small impact on the environment. Unlike the turbine blades that spin in huge
hydropower plants like the Hoover Dam, an Archimedes screw permits fish to swim
through it and emerge at the other end almost unscathed.
Such
generators have been built in Europe, including one commissioned by Queen
Elizabeth II of England to power Windsor Castle; the first in the United States
could start operating next year.
And
Archimedes’ ideas are showing up in other fields as well.
“He just
planted the seeds for so many seminal ideas that could grow over the ages,”
said Chris Rorres, an emeritus professor of mathematics at Drexel University,
who organized the conference at N.Y.U.
A panoply
of devices and ideas are named after Archimedes. Besides the Archimedes screw,
there is the Archimedes principle, the law of buoyancy that states the upward
force on a submerged object equals the weight of the liquid displaced. There is
the Archimedes claw, a weapon that most likely did exist, grabbing onto Roman
ships and tipping them over. And there is the Archimedes sphere, a forerunner
of the planetarium — a hand-held globe that showed the constellations as well
as the locations of the sun and the planets in the sky.
“Here was
someone who just changed how we look at the universe,” Dr. Rorres said.
Only a
handful of Archimedes’ writings survive, and much of what we think we know
about him was written centuries after his death.
Some of the
legends, like using mirrors to set the Roman ships afire, proved too good to be
true. The same may go for the tale of Archimedes figuring out, while sitting in
a bathtub, how to tell if the maker of a crown for the king had fraudulently
mixed in some silver with the gold; according to this story Archimedes, too
excited to put on clothes, ran naked through the streets of Syracuse shouting,
“Eureka!”
As with the
mirrors, the underlying principle works. But in practice, the tiny difference
in volume between a crown made of pure gold and one made of a mixture of gold
and silver is too small to be reliably measured.
Some of the
talks at the conference were about using present-day ingenuity to figure out
what Archimedes actually achieved in antiquity.
Michael
Wright, a researcher at Imperial College London, has been trying to decipher
how the Archimedes sphere showed the night sky. Although it is described in
historical writings, no pieces or even drawings of it have survived. Others had
already made celestial spheres, globes that show the positions of the
constellations.
The Roman
historian Cicero described the Archimedes sphere as uninteresting at first
glance until it was explained. “There was a wonderful contrivance due to
Archimedes inside,” he wrote. “He had devised a way in which a single rotation
would generate the several non-uniform motions.”
If this
description is taken literally, it would seem that Archimedes figured out the
gearing needed to mimic the motion of the planets, including the retrograde
motion where they appear to stop and reverse direction for a while before
proceeding in their usual direction.
“This
instrument was just like any other celestial sphere, except with the addition
of indicators for the Sun, Moon, the planets moving over the sphere and a
mechanism inside the sphere to move them,” Mr. Wright said.
In the
spring, he began building his version of the Archimedes sphere. He presented it
in public for the first time at the conference.
“I can’t
guarantee that the original was like this,” Mr. Wright said. “What I can say is
this, in the simplest way that I can imagine it, fits the evidence we have.
We’ve been talking for 2,000 years about this thing that Archimedes made, and
nobody seems to have offered to show people what it was like. I had an idea. I
thought it was worth making, even if it was so people could have an argument
about it and disagree with it. That’s a good way to get things going.”
Dr. Rorres
said the singular genius of Archimedes was that he not only was able to solve
abstract mathematics problems, but also used mathematics to solve physics
problems, and he then engineered devices to take advantage of the physics. “He
came up with fundamental laws of nature, proved them mathematically and then
was able to apply them,” Dr. Rorres said.
Archimedes
oversaw the defenses of Syracuse, and while death ray mirrors and steam cannons
(another supposed Archimedes invention debunked by “Mythbusters”) were too
fanciful, the Archimedes claw appears to have been a real weapon used against
the Roman navy.
It is very
likely that it took advantage of two scientific principles Archimedes
discovered.
With his
law of buoyancy, he was able to determine whether a paraboloid (a shape similar
to the nose cone of a jetliner) would float upright or tip over, a principle of
utmost importance to ship designers, and Archimedes probably realized that the
Roman ships were vulnerable as they came close to the city walls.
“Archimedes
knew about the stability of these kinds of ships,” said Harry G. Harris, an
emeritus professor of structural engineering at Drexel who has built a model of
the claw. “When it is moving fast through the water, it is stable. Standing
still or going very slow, it is very easy to tip over.”
So using an
Archimedean principle — the law of the lever, which enables a small force to
lift a large weight, as in seesaws and pulleys — a claw at the end of a chain
would be lowered and hooked into a Roman ship, then lifted to capsize the ship
and crash it against the rocks.
Syracuse
won the battle but was weakened under a long siege and fell three years later.
And in 212 B.C., at the age of about 75, Archimedes was killed by a Roman
soldier, supposedly furious that he refused to stop work on a mathematical
drawing. His last words: “Do not disturb my circles!”
Of course,
that bit about the circles is probably also a myth.
A version
of this article appeared in print on June 25, 2013, on page D2 of the New York
edition with the headline: Archimedes: Separating Myth From Science.
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