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Pizza tossing for science |
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Associate Professor James Friend (middle) and PhD student, Daniel (Kuang-Chen) Liu, studied the art and science of pizza tossing, as part of their research into standing wave ultrasonic motors (SWUMs).
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Diagram from Monash University Dynamics of pizza tossing
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Everyone loves pizza and the theatre of watching the local pizza maker toss the dough into the air before stretching it onto the pan, covering it with delicious ingredients and shovelling it into the oven. Pizza tossing has long been thought of as an art and is now being considered a science.
Indeed, researchers at Monash University have studied the toss in what they describe as a variation of the "classic bouncing ball problem" - a principle commonly used in schools and universities to understand physics.
In this case, the ball has been replaced with a disc (pizza dough), and the researchers have investigated the way the disc interacts with the pizza-maker's hands before undergoing a combined angular and linear oscillation along the vertical axis.
Why study pizza? Well, according to the team, who recently published a paper entitled The behaviour of bouncing disks and pizza tossing in EPL (A letters journal exploring the frontiers of physics), there are many interesting and non trivial questions related to pizza tossing, including what kind of thickness distribution will the tossed pizza dough form? And, how should the material property of the dough be modelled?
Perhaps more importantly, by unlocking the physics of the perfect pizza toss, improvements could be made to the design of the next generation of standing wave ultrasonic motors (SWUMs), which operate on similar principles to pizza tossing.
Daniel (Kuang-Chen) Liu, a PhD student supervised by Associate Professor James Friend, and Senior Lecturer, Leslie Yeo, videotaped a professional pizza tosser at work for analysis.
The team, from Monash's Micro/Nanophysics Research Laboratory, then calculated how best to describe the way the dough travelled through the air -- including how much the dough rotated, how quickly it spun, its stability and the energy efficiency of the toss itself.
The result was a set of nonlinear differential equations that captures the art of pizza tossing.
"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," explained James.
"If you are tossing the pizza continuously, not stopping to catch it and stop every time, then your hands should move in circles."
SWUMs operate on similar principles and 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.
"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," explained James.
"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."
Scientists around the world have been using trial and error to make variations of the SWUMs, and while some may have worked, there has not been a thorough understanding of the forces involved until now.
"The maths are a bit tricky, but the most puzzling questions with SWUMs are answered in this study," said James.
"We think that further investigation of the work will prove fruitful for the understanding and design of SWUMs."
The scientists involved in this study made headlines in January this year after developing the world's smallest motor - or microbot - just one quarter of a millimetre wide.
These motors are now being considered for use in the propulsion system of miniature machines that can be injected into the human bloodstream as an aid to complex surgical operations necessary to address blockages in the bloodstream.
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According to the study, of the two basic pizza tossing methods, the helical trajectory used in single tosses maximises rotational speed and efficiency.
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The classic 'bouncing ball problem' refers to a typical science experiment where a ball is dropped from a height, bounces off the ground, and rebounds to the same height. The experiment displays a range of intriguing phenomena.
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An ultrasonic motor is a type of electric motor formed from the ultrasonic vibration of a component, the stator, placed against a rotor or slider, depending on the scheme of
operation.
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Canon was one of the pioneers of the ultrasonic motor, incorporating the "USM" into its autofocus lenses.
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Pizza tossing and SWUMs share a common mechanism for converting reciprocal input into continuous rotary motion.
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Depending on who you listen to, the pizza was invented by the Phoenicians, the Greeks, the Romans - or anyone who learned the secret of mixing flour with water and heating it on a hot stone. However, most people believe it was the Greeks who came up with the idea of baking bread in round, flat shapes and adding things on top.
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The most famous pizza chef in history was the Italian baker, Raffeale Esposito, who first added cheese to bread and then put sauce underneath it. His creation became so popular that, in the 19th Century, Umberto I, King of Italy, and his wife, Queen Margherita di Savoia, invited Esposito to their palace to taste his speciality.
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