September 11th, 2005
Why spaghetti does not break in half
As we are Sunday, you might have more time to spend in your kitchen than during week days. So try a little experiment: take a dry spaghetti, and bend it until it cracks. How many pieces do you think you’ll get? Two? Wrong. An uncooked spaghetti can break into three, seven or even ten pieces, but rarely two. It’s even rumored that Nobel laureate and physicist Professor Richard Feynman has used lots of pasta to solve this mystery. But now, according to ABC Science Online in "Cracked! The secret life of spaghetti," two French physicists say the answer is related to elastic waves travelling along the pasta when dry spaghetti is bent and suddenly released at one end. And don’t think this is a minor discovery: the researchers think their findings can be applied to civil engineering to make structures like buildings and bridges more stable.
Let’s start with an introduction by ABC Science Online.
Physicists have settled one of science’s more perplexing enigmas by explaining why uncooked spaghetti breaks into more than two pieces when you bend it.
French physicists Dr Basile Audoly and Dr Sébastien Neukirch say the answer is related to waves of vibration that pass through the pasta when dry spaghetti is bent and suddenly released at one end.
Below are two pictures of a dry spaghetti bent until it breaks in several pieces, before and after the breaking (Credit: Université Pierre et Marie Curie, Paris, France ).
These images have been extracted from a movie that you can see on a page maintained by the two French scientists, "How bent spaghetti break," along with other movies.
Of course, the physicists didn’t only shot movies.
[After taking high-speed images of these broken spaghetti,] they applied the Kirchhoff equation, an equation that relates to how waves travel through an object that’s put under stress. The researchers conclude that spaghetti fragmentation is caused by a burst of flexural, or elastic, waves that travel along the spaghetti after the initial break.
And they added that this "physical process of fragmentation is relevant to many areas of science and technology," a fact confirmed by Rod Cross, a professor of physics at the University of Sydney, Australia.
"If you can understand how spaghetti breaks you can understand how anything else breaks including a building an aeroplane or a car," he says. "Under impact they’ll all vibrate and break. More to the point it can be a human leg, because if you whack a human leg it’ll probably break in three or four bits as well for the same reason."
Oooch! What an example!
For more information, this research work has been published in Physical Review Letters under the name "Fragmentation of Rods by Cascading Cracks: Why Spaghetti Does Not Break in Half" (Volume 95, No. 9, article number 095505, August 26, 2005).
Here are two links to the abstract and to the full paper (PDF format, 5 pages, 366 KB).
Sources: Judy Skatssoon, Australian Broadcasting Corporation (ABC), Science Online, September 7, 2005; and various web sites
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