Pasta alla Fisica

[Чатский]

Materials science

Pasta alla fisica

Aug 11th 2005

From The Economist print edition

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 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?

[beatnik]

Hummm... Physics of food... :hm:

Talking about pasta, I’m puzzled myself what’s the idea behind the different pasta shapes and their proper combinations with pasta sauce...?

[Чатский]

The problem was actually highly non-trivial.

The issue with pasta shapes has to do with texture and esthetics. For example, my favorite pasta is Castellane - these are fairly thick curled shells, they are more chewy as compared to, say, linguini or garden variety spaghetti.

[beatnik]

The problem was actually highly non-trivial.

The issue with pasta shapes has to do with texture and esthetics. For example, my favorite pasta is Castellane - these are fairly thick curled shells, they are more chewy as compared to, say, linguini or garden variety spaghetti.