If pizza isn't already on the list of 7 greatest inventions of the post-modern world (because nothing goes with wanting to strangle someone who invokes Foucault like a nice slice of pepperoni) a new discovery may put it there; the physics of the perfect pizza toss have inspired Monash University to design the next generation of micro motors  ... thinner that a human hair.

Daniel (Kuang-Chen) Liu, a PhD student supervised by Associate Professor James Friend and Senior Lecturer Leslie Yeo from Monash's Micro/Nanophysics Research Laboratory, videotaped a professional pizza tosser at work.   They then calculated how best to describe the way the dough travels through the air – including how much the dough rotates, how quickly it spins, its stability and the energy efficiency of the toss itself.

The result - a set of nonlinear differential equations that captures the art of pizza tossing.  Almost as importantly, the model could help researchers to design the next generation of standing wave ultrasonic motors (SWUMs), which operate on similar principles as pizza tossing. 



The tiny motors have the potential to be used for minimally invasive neuro-microsurgery. In these electric motors, the fixed component, the stator, is made to vibrate ultrasonically, and this causes the moveable part, the disc-like rotor, to be "tossed" – both rotated and lifted. 

"In brief, if you toss a pizza dough one toss at a time – that is, if you toss then catch – your hands should move in a helical fashion, like they are moving along a spiral, a curved line laid along a cylinder," Friend said.   "If you are tossing the pizza continuously, not stopping to catch it and stop every time, then your hands should move in circles.  The SWUM works exactly like a pizza chef tossing dough, with the hands representing the vibrating stator of the SWUM and the dough representing the rotor. The difference is only in the details: a chef tosses dough, about once a second, a few tens of centimetres into the air. A SWUM tosses the rotor a few million times a second into the air."

He said scientists around the world have been using trial and error to make variations of the SWUMs, and while they might have worked, there had not been a thorough understanding of the forces involved until now.


Who knew pizza dough was so interesting?

"Some of the maths are a bit tricky," Friend said. "The most puzzling questions with SWUMs are answered in this study. We think that further investigation of the work will prove fruitful for the understanding and design of SWUMs."

The scientists are the same principals who recently developed the world's smallest useful motor, only a quarter of a millimetre wide, that could be used in the propulsion system of miniature machines to swim through the bloodstream to inaccessible places, potentially revolutionising future surgical procedures.

Article: K.-C. Liu, J. Friend and L. Yeo, 'The behavior of bouncing disks and pizza tossing', EPL 85 60002 (5pp) doi: 10.1209/0295-5075/85/60002