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Do Corked Wood Bats Have a Trampoline Effect?
Every once in a while, MLB players are caught trying to cheat by using illegally altered bats or substances. On June 3, 2003, Chicago Cubs outfielder Sammy Sosa was caught using an il- legal corked bat. A few years earlier, in 1998, Sosa had capti- vated fans in an exciting race with St. Louis Cardinals’ first baseman Mark McGuire in an attempt to break Roger Maris’ long-standing record of 61 home runs in a single season. So- sa’s illegal bat had a long hole (filled with cork) drilled down the center of the wood barrel (Russell, 2012). A question fre- quently posed about such illegally altered wood bats is, “Does a corked bat has a trampoline effect?” It turns out that a cork- ed bat does indeed have hoop modes, but the frequency of the (n = 2, m = 1) hoop mode is well above 5,500 Hz, so high that it provides absolutely no improvement in performance over a solid bat. In fact, experimental measurements of bat perfor- mance reveal that a corked bat actually has a lower BBCOR than a solid bat and thus provides no physical performance advantage to a hitter (Nathan et al., 2011b).
The acoustic and vibrational characteristics of baseball bats described in this article are easily applicable to any other sport involving hand-held sticks, rackets, or clubs. The flexural bending vibrations of cricket bats and field hock- ey sticks play a similar role in the problem of sting and the identification of the sweet zone. Tennis rackets have flexural bending mode shapes as well as torsional modes that influ- ence the vibration felt in the handle. The strings of a tennis racket vibrate like a membrane (drumhead) and the face of a golf club driver has mode shapes like a plate clamped at the edges. Both of these produce a trampoline effect that affects both the efficiency of the impact with the ball and the per- ception of quality for the player hearing the impact sound.
There is a wealth of opportunities for research on the acous- tics and vibration of sports equipment. Understanding how an implement vibrates is the first step toward finding ways to minimize the vibration causing sting or injuries in the hands and arms. Understanding the trampoline effect in bats, rack- ets, and clubs is necessary for developing scientific tests to measure and regulate performance. Acoustics tools could be used to detect equipment that has been illegally altered. Com- posite materials and new innovations in equipment design can lead to implements that perform better and/or that provide a more desirable feel of the hands and ears of the player. And an awareness of acoustics could even enhance the enjoyment of watching a favorite player hit a home run to win a game.
  Dan Russell is a professor of acoustics and distance education coordinator for the Graduate Program in Acoustics at Penn State. He has been studying the acoustics and vibration of sports equip- ment (baseball and softball bats, ice and field hockey sticks, tennis rackets, crick-
 et bats, hurling sticks, golf drivers, putters and balls, ping- pong paddles, and basketballs) for 20 years. He has provided consulting and testing services for several manufacturers including Easton, Louisville Slugger, DeMarini, Marucci, Combat Baseball, Donnay Tennis, and Nike Golf and serves as a scientific advisor for USA Baseball. His animations web- site ( is well-known in the acoustics education community.
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