2010-08-20

The Breaking Spaghetti Mystery

The spaghetti mystery that baffled a Manhattan Project scientist



Why do strands of spaghetti so rarely snap into only two pieces? Take a look at the solution to a mystery that, no fooling, baffled famed physicist Richard Feynman.



Feynman's Interest in Spaghetti

In a 1993 Nova program (by film-maker Sykes) and the 1994 book "No Ordinary Genuis" (edited by Sykes) Daniel W. Hillis fondly recalls an evening with Feynman breaking spaghetti, unsuccessfully trying to discover why it breaks in three pieces.
Here is a video snippet of the interview:
Spaghetti Stumps The Chief. 150KB, 60 secs

The seemingly simple problem was succinctly posed by Hillis as "Why does spaghetti break in 3 pieces?" ...

Collected from: Feynman Videos

How bent spaghetti break


Bent dry spaghetti do not break in half but instead in three or more pieces. With the aim to explain this surprising phenomenon, we studied a related problem, namely the dynamics of an elastic rod that is bent quasi-statically and then suddenly set free. Counter-intuitively, we find that the mere release of the rod induces a stress increase. The multiple breaking of bent rods, like dry spaghetti pasta, can then be understood as a cascade of releases (loss of cohesion upon breakings) followed by stress increases leading to new cracks.

Collected from: Breaking spaghetti







Breaking spaghetti - short story

B. Audoly, S. Neukirch

[...]


Experiment. To study the dynamics of the rod following the first breaking event, we introduce a catapult experiment: a rod is bent quasi-statically and then suddenly released at one end. [...]

Elastic model. We used the Kirchhoff equations for elastic rods to study the dynamics of the rod in this catapult geometry. When released, the rod follows three regimes successively: (1) the released end quickly straightens up at short times, giving birth to a burst of flexural waves that (2) travel along the rod to the clamped end and (3) are amplified by reflexions on the opposite (clamped) edge.


[...]

 Conclusion We have shown that releasing an elastic brittle rod from a bent configuration is sufficient to make it break. This counter-intuitive result explains why brittle rods break in several pieces when bent beyond their limit curvature: a first breaking occurs when the curvature exceeds its limit value in some place, after which, as described above, flexural waves travel along the two newly formed halves of the rod, where they locally increase the curvature further. This increase leads to new breakings that give rise to new travelling waves, and a cascade mechanism can take place.


Sources
The mystery of spaghetti that baffled a Manhattan Project scientist
http://io9.com/5613155/when-spaghetti-snaps
Feynman Videos
http://heelspurs.com/feynman.html
Breaking spaghetti
http://www.lmm.jussieu.fr/spaghetti/
YouTube - Breaking Spaghetti
http://www.youtube.com/watch?v=I7qPrSeIHKM
YouTube - Breaking dry spaghetti
http://www.youtube.com/watch?v=8GutricnMNc
Breaking spaghetti - short story
http://www.lmm.jussieu.fr/spaghetti/short_story.html

Related
Movies - Breaking spaghetti
http://www.lmm.jussieu.fr/spaghetti/movies-6-more.html
Why spaghetti does not break in half | ZDNet
http://www.zdnet.com/blog/emergingtech/why-spaghetti-does-not-break-in-half/17
Buckling Spaghetti - Faster Than Euler
http://www.math.psu.edu/belmonte/spaghetti.html


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