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Corked Bats, Juiced Balls and Humidors

No one should cheat in baseball . . . but if you're going to, you might want to read a recently published paper in the American journal of Physics first.

I think it's safe to say that no sport has been the subject of more physics analyses than baseball. Robert Adair's book The Physics of Baseball is now in its third edition, and remains one of the most popular "Physics of . . ." books on the market.

Adair did a great job analyzing statistics and baseball phenomena, from the challenge of getting a hit to the ideal path around the bases. For the most part, Adair relies on insightful applications of theory to the sport and breakdowns of actual baseball stats. Sometimes, though, to learn about baseball, you're gonna have to hit a few balls.

If you're a careful physicist, however, you don't actually swing the bat - that's too inconsistent. Instead you design a system that makes your experiments as repeatable and consistent as possible. That's exactly what a group of physicists did in a paper appearing in the June issue of the American Journal of Physics. Alan Nathan, Lloyd Smith, Warren Faber and Daniel Russell specifically decided to study three factors affecting the way the ball rebounds off the bat.

Corked Bats

The first experiment they describe involved firing a baseball from an air cannon and hitting either a regular wood bat or a corked bat to test how well the ball rebounded from each. Although some people have speculated that the walls of a hollow bat might act a bit like a trampoline - collapsing a bit and then rebounding to give the ball an extra kick - that doesn't turn out to be the case. The experiment showed that balls bounce better off of solid bats than hollow or corked ones. While it seems likely that the lighter corked bats might help a batter get more hits, the result is likely to be a ball that doesn't fly quite as far because a lighter bat transfers less energy to the ball.

On the other hand, unlike experiments performed on the Myth Busters, corked bats aren't a whole lot worse than solid bats when it comes to hit distance. It seems that home run hitters should stick with solid bats, but a really desperate, mediocre batter may connect more often and more solidly with a lightened bat, perhaps even picking up a homer on occasion. (Of course, they will pay hefty price if they get caught.)

Juiced Balls

In their second experiment, the physicists wanted to determine whether some baseball conspiracy theorists are right in their claims that modern baseballs are livelier (bounce better) than balls of previous eras. So called "juiced balls" are often blamed for the startling increase in home run hits in recent decades.

Once again, the scientists used their cannon to fire a selection of balls at either a bat or a steel plate in order to record how well the balls bounced. Fortunately, they had access to an unopened cache of balls (donated by the family of Oakland As former owner Charlie Finley) from the late 1970s, before the supposed juiced ball period began. In comparing the vintage balls with brand new official balls from Rawlings, they found that the older balls were less consistent, but on average no more or less lively than modern balls.

It's unlikely that the experiment will put conspiracy theorists at ease, but I think it would be wise to look at other explanations for rising home run hit numbers. (Can you say "steroids"?)

Humidors in Denver

The higher you go, the lower the air density, and the farther you will be able to hit a ball on average. That makes the mile high stadium of the Colorado Rockies a great place to be a batter, but a lousy place to be a pitcher.

In order to cool off the hitting a bit at their home town venue, the Rockies decided to try storing baseballs in a humidor, under the assumption that moist balls don't bounce as well, which should in turn keep batted ball distances down.

In order to test that assumption, the researchers turned to their cannon and found, sure enough, that the higher the humidity where the balls are stored, the less well they bounce.

Under further research, however, they also showed that there is another factor that affects balls about as much as humidity - temperature. Warming the balls increased their liveliness, regardless of the humidity, and cooling them reduced liveliness. Although it's hardly proof, the revelation adds a bit of credence to the rumor that some unethical managers over the years have attempted to ensure that the opposing team received a chilly batch of balls when they were pitching, and the home team had access to a warmed supply when they were on the mound.


Although the published baseball physics paper is available only to subscribers to the American Journal of Physics, you can see a preprint of the paper for free on the physics ArXiv.


  1. Thanks for the great story. i had a great conversation with my baseball loving teenaged son and husband because of it.


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