The skin of sharks is covered with scales called denticles. This image, 250 µm across, of the skin of a bonnethead shark shows the details of typical denticles, with three surface ridges leading to three prongs oriented toward the tail. Related in structure to teeth, denticles have long been suspected of reducing hydrodynamic drag on sharks as they swim. Indeed, shark skin has inspired a variety of materials engineered to reduce drag on submerged bodies; swimsuits are perhaps the best-known example. (For more on swimsuit technology, see Physics Today, August 2008, pages 32 and 84.)

Many of the experimental studies of such materials—and of shark skin itself—have examined the drag on rigid bodies, a scenario that may be relevant for some applications but not for sharks or swimmers. New work by Johannes Oeffner and George Lauder of Harvard University has now looked at the effects of undulation. The pair...

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