[Paleopsych] Economist: Materials science: Pasta alla fisica
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Materials science: Pasta alla fisica
http://www.economist.com/science/PrinterFriendly.cfm?Story_ID=4269826
Aug 11th 2005
Physicists have solved the long-standing puzzle of how spaghetti
breaks
IT WAS a problem that baffled the master himself. Richard
Feynman--maverick physics genius, Nobel laureate and father of modern
quantum theory--could not work out why, when a strand of dried
spaghetti is snapped, it almost never breaks in half but instead
fragments into three or more pieces. At dinner with Daniel Hillis, an
old friend and computer scientist, the two became obsessed with this
and spent hours theorising and experimenting. In the end, they left
with a kitchen full of pulverised pasta and no reasonable answer.
Basile Audoly and Sébastien Neukirch of the University of Paris VI
think, however, that they have succeeded where Feynman failed. Their
calculations, revealed in a forthcoming paper in Physical Review
Letters, suggest that the key to the problem lies in so-called
flexural waves. Each time part of a bent strand breaks, a series of
these waves ripples down the length of the pasta. The mistake Feynman
probably made was to assume that the strain released when a bent
strand breaks allows the two half-strands to relax and become straight
again. Instead, according to their equations, the passing waves cause
parts of the daughter strands to curve even further. This triggers
other breakages which, in turn, trigger further waves, causing the
strand to fragment.
To put their mathematical solution to the test, they devised a
rigorous experiment. And, like all good researchers, they describe
their materials and methods in a way that allows others to repeat what
they did: "A Barilla no. 1 dry spaghetti pasta of length L=24.1cm was
clamped and bent into an arc of circle," they write. "Twenty-five
experiments were carried out with various pasta diameters." By
snapping 1,000 photos per second as they released the bent strands,
they were able to see the travelling waves and to show that the motion
of the strands followed their equation exquisitely. Videos of all this
can be viewed [4]here.
Dr Audoly's and Dr Neukirch's research does have a serious point, of
course. The steel struts that help to hold up skyscrapers and bridges
are slightly less trivial examples of thin rods whose tendency to
break needs to be understood. Knowing the mechanisms by which these
rods fragment is important not only for designing such structures but
also for reconstructing what has gone wrong when one fails.
Having out-thought Feynman, though, it is hard to see what should be
next on the pasta research agenda. Perhaps a suitably profound problem
is that of the slowing down of time--a well-established part of the
theory of relativity. Or, to put it in pasta terms, does a watched pot
take longer to boil?
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