"Smart materials" are already a big hit in sports. In baseball, for instance, new aluminum bats can now quiet the "bees" a player feels when hitting a ball off the handle. Likewise, smart skis can damp vibrations as needed. The "active" part of these sporting goods is a credit-card-sized wafer that uses quirky but well-studied materials called piezoelectrics. These compounds convert mechanical stresses, such as vibrations, into an electric signal (which can be harmlessly shunted), or, conversely, change shape or size in response to electricity.

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