科学美国人60秒:Pasta Problem Cracked!

Physicists concern themselves with problems that are profound. The origins of the universe, the nature of time, the composition of matter. And then, there’s spaghetti. A pasta problem has perplexed physicists as celebrated as Richard Feynman, and has even been awarded an Ig Nobel prize. At issue:

“Why spaghetti doesn’t break into two pieces. Why it breaks into three pieces or more.”

Ronald Heisser, now a grad student at Cornell, decided to explore the misbehavior of spaghetti for an undergraduate math course he took at MIT.

Now, you may never have noticed it, but it’s nearly impossible to break a single, dry piece of spaghetti in half. Feynman allegedly noodled with the puzzle. And Heisser became similarly possessed.

“I’m a little bit of a contrarian person. So I thought it would be fun to try and break it into two. ‘Cause no one said you couldn’t do that. They just said why it doesn’t break into two.”

In fact, the French researchers who were awarded the Ig Nobel prize in 2006 found that when spaghetti is bent evenly from both ends it will crack near the center, where the stick is most curved. But this initial break sets up a vibrational wave that quickly fractures the rod further. So you get multiple fragments.

What Heisser wondered was whether he could somehow get around this vibrational “snapback” effect. And he found you have to do the twistHeisser built a device for torquing his pasta with precision and he observed the resulting fragmentation with a high-speed camera. He discovered that introducing a twist of around 360 degrees to the long strand allowed him to produce the desired single pair of pasta pieces.

That’s where Vishal Patil, a grad student in mathematics at MIT, comes in:

“So I first heard about this spaghetti problem from coauthors Ronald Heisser and Professor Jörn Dunkel when I first arrived at MIT…and after hearing about this problem, I became interested in developing mathematical models for the fracture of this elastic rod. And in particular, to see if using this model you could find out ways to control the fracture in the rod.”

Controlling fractures is a big issue in materials science and could have applications in everything from the design of highways and bridges to the engineering of nanotubes.

Patil’s modeling showed that twisting the spaghetti dampens the snapback effect. That’s because once the twisted stick is broken, it will try to unwind. This rapid unwinding creates a “twisting wave” that basically blocks the vibrational snapback wave, leaving the spaghetti in two clean pieces. The work is served up in the Proceedings of the National Academy of Sciences. [Ronald H. Heisser et al., Controlling fracture cascades through twisting and quenching]

VP: “Although the project was a bit of fun I think it’s quite nice when you can find interesting physics and maths lurking behind everyday, mundane objects.”

—Karen Hopkin