Scientists Crack Spaghetti Snapping Mystery

(Inside Science) -- It is nearly impossible to snap a dry spaghetti noodle neatly in two -- a challenge that has confounded pasta-loving researchers for decades. Now scientists from MIT have finally figured out how to break such noodles in two -- with a twist. These findings may help shed light on how cracks form and how to control breaks in other kinds of rods, such as carbon fibers in golf clubs and helicopter blades, or even microtubules in cells.

If one holds a spaghetto -- a single stick of spaghetti -- at both ends and bends it until it breaks, the result is usually three or more fragments. Why these noodles do not just snap in half is a mystery that even Nobel laureate Richard Feynman could not crack after a few hours of breaking spaghetti in a kitchen .

In 2005, French physicists finally solved this puzzle , earning themselves the 2006 Ig Nobel Prize in physics . They found that when a stick of spaghetto or any long thin brittle rod is bent, it will first break near the center where it is most curved, and the subsequent force emanating from the snap would trigger additional fractures further down the stick, breaking the rod into more than two pieces.

One question remained -- could a spaghetto ever be snapped in half? Now scientists find this is possible if one twists the noodle as one bends it. “It’s possible to control fracture quite accurately with twist,” said study senior author Jörn Dunkel , an applied mathematician at MIT.

This research began when students at MIT decided to tackle the problem after taking a nonlinear dynamics course Dunkel taught. “Our students were not happy with accepting ‘well, that’s not possible’ as an answer, but rather were asking ‘why not?’ and ‘how could we make it possible?’” Dunkel said.

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To carry out their experiments, study co-lead author Ronald Heisser, now a mechanical engineer at Cornell University, built a device to controllably twist and bend spaghetti, involving two clamps to hold a spaghetto. One clamp rotated to twist the stick, while the other could slide toward the twisting clamp to bend the noodle. The samples were stored in airtight containers to limit any effects humidity and temperature might have on the noodles.

The researchers bent hundreds of spaghetti sticks, recording their fragmentation with a camera at up to a million frames per second. They found that by first twisting a noodle nearly 360 degrees and then slowly bringing the two clamps together to bend it, the stick snapped exactly in half. These results were consistent across two kinds of spaghetti -- Barilla No. 5 and Barilla No. 7, which have slightly different widths.

At the same time, study co-lead author Vishal Patil, an applied mathematician at MIT, developed a mathematical model to explain how twisting can help a rod crack in half. According to the model, the corkscrewing motions the stick makes, as its twisting unwinds after the fracture, help dampen the force that could have caused additional breaks. This model’s predictions matched the experimental findings.

“It is amazing how a little twist can so radically change the solution to a problem,” said physicist Arshad Kudrolli at Clark University in Worcester, Massachusetts, who did not take part in this research.

The model should apply to many other rodlike structures, such as the microtubules making up the internal scaffolding of cells, or carbon nanotube fibers researchers seek to incorporate into advanced composite materials.

“This study is important to understanding catastrophic failure in materials science, as well as the development of materials that are lighter and stronger using nontraditional engineering materials,” Kudrolli said.

Future research could explore how twisted bundles of fibers behave. In such cases, friction between the fibers “can lead to interesting changes in the fracture behavior,” Dunkel said.

“We hope our work encourages younger and older folks to look around them and find and appreciate interesting physics phenomena in everyday life,” Dunkel said.

The scientists detailed their findings online August 13 in the Proceedings of the National Academy of Sciences.