Biomechanics: The wonders of whirl

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John E. Moalli and Adam P. Summers relish a book on biomechanical spin, from wheels to free-falling felines.

Why the Wheel Is Round: Muscles, Technology, and How We Make Things Move

Steven Vogel University of Chicago Press: 2016. ISBN: 9780226381039

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INTERFOTO/Sammlung Rauch/Mary Evans Picture Library

A hypothetical sixteenth-century reading machine.

In Why the Wheel Is Round, biomechanist Steven Vogel (who died last year) succeeds once again in turning engineers, biologists and the general public onto the beauty, complexity and approachability of his field. He spins an 11-part tale of circular motion that ranges from rotation in biology to rotation driven by biology. Vogel captivates with discussions of engineering feats rooted in circular motion — from plodding horses turning shallow paddle wheels to gears that drive sixteenth-century reading machines — and doesn't stint on his trademark puns and word-play. Mixing findings in his own field with those from mechanics, dynamics and historical analysis, he creates a delightful perspective on the wonders of whirl. There is even a bonus chapter on how to make simple rotational models, including an entertaining but difficult-to-use drill. Let the good times roll.

The book begins with the lack of macroscopic wheels in biology — an area that Vogel touched on in Cats' Paws and Catapults (W. W. Norton, 2000). Notwithstanding whole organisms that tumble and spin, such as the tumbleweed and escaping wheel spiders (Carparachne aureoflava), Vogel points out that natural selection has been nearly incapable of producing a freely rotating joint. The only body part that can rotate unimpeded through more than 360 degrees is the bacterial flagellum.

Yet the usefulness and, in many cases, efficiency of rotational movement are such that Vogel proffers many biological examples of how linear motion is translated into rotational, as when contraction of muscle drives rotation of a beater to generate the aptly named huevos revueltos (Spanish for scrambled — literally 'revolved' — eggs).

From wheels and carts to bearings and shafts, cranks and drive mechanisms, each chapter is a historically informed circumambulation of an aspect or manifestation of rotation. For instance, which came first, the cart wheel, or the potter's wheel, used to fashion portable receptacles? (The answer revolves around the bearing.) The many period illustrations are fascinating: you're compelled to work out the mechanisms of a mule-driven arrastra, a nineteenth-century ore crusher. Some reveal an ingenuity surprising for their era and encourage the reader to appreciate the simplicity with which engineers and designers tackle difficult tasks. The Italian engineer Agostino Ramelli's 1588 picture of an inclined turntable on which a miller would walk in place to turn grinding stones is one such. In other cases, the illustrations challenge your mechanical intuition. Two interlocking elliptical gears from a 1907 image by Gardner Dexter Hiscox look like they will simply jam when rotated. In fact, they turn a constant rotation into an output that is at first faster, then slower, than the input.

From the hidden rotation of a tape measure in its case, through 'true cranks' and treadmills, to how dough creeps up a spinning beater, there are lessons to be learnt. Vogel imparts a cheering numerical understanding, and outlines the possibility of new technologies that leverage under-appreciated concepts. One of these is the zero angular momentum turn — an apparent impossibility demonstrated by a cat righting itself during a fall. No angular momentum is imparted at the outset but, through contortions and twists, the feline reorients along its longitudinal axis.

This marvellous ability has never been exploited technically, but Vogel encourages speculation about use in robotics or microelectromechanical systems. It might even serve as a metaphor for the elegance and ingenuity that make this book so fun to read.

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