The Physics of Cheating in Baseball

Corked bats and juiced balls have long plagued baseball, but do they really help a player’s game? Four scientists found surprising answers

The issue of juiced baseballs surfaces every couple years during the month of April due to a high rate of home runs hit. (Ed Wolfstein / Icon SMI 756 / Ed Wolfstein / Icon SMI / Newscom)

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But is the humidor really to thank (or blame) for the decrease in home runs?

To test the theory, the authors placed several dozen balls in conditions ranging from 11 percent to 97 percent relative humidity for weeks, and temperatures from the 30s to nearly 100 degrees, then fired them against metal cylinders that approximate bats. Again measuring the coefficient of restitution, they found that the colder and moister a ball was, the less bounce it had. Translation: a ball hit on a hot dry day at an Arizona ballpark will go noticeably farther than the same ball hit on a frigid, foggy day at Boston’s Fenway Park.

As for Denver’s Coors Field, the researchers calculate that a humidity increase from 30 percent to 50 percent would take 14 feet off a 380-foot fly ball—enough to decrease the chances of a home run by 25 percent.

Not long ago, Nathan says, a reporter in Arizona contacted him and told him that the Arizona Diamondbacks were considering installing a humidor at their stadium, too. Nathan did the math—this time starting at the desert-air base-line of 20 percent relative humidity, and conditioning balls to 50 percent relative humidity. “That would be an even greater reduction in the number of home runs, more like 37 percent,” he says.

The Diamondbacks later put those plans on hold. Everybody, it seems, likes at least a few homers between their peanuts and Cracker Jack.

Christopher Solomon is a writer in Seattle. In Little League, coaches usually stuck him in right field.


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