Web edition: March 7, 2013
Print edition: March 23, 2013; Vol.183 #6 (p. 32)
Picture sitting at a baseball park, leisurely watching a game. Your mind wanders, torn between a box of Cracker Jack and the conversation drifting down from the row behind you. Suddenly the crack of a bat snaps you to attention, and you scan the field for the ball. Physicist Alan Nathan would say your attention is piqued because well-hit balls make a different noise than weak pop-ups do.
“You hear a high-frequency sound,” says Nathan (below). There’s a duller thud when the ball misses the bat’s “sweet spot,” he says, the point where a hit maximizes the outgoing speed of the ball.
Physics and baseball are a natural marriage, as Nathan realized 16 years ago when he took a break from experimental particle physics to talk to high school kids about science and casually chose baseball as the topic. He got hooked and spent a whole sabbatical analyzing the bat-ball collision, the dynamic core of the sport.
His early work centered on the idea that the energy of the collision must go somewhere, and he spelled out how much gets transferred to the ball and how much is lost as vibrations run down the bat. Nathan recently tallied the average speed needed for a hit ball to leave each major league park. It turns out that players really need to whack a ball to launch it in Atlanta and Phoenix — not so much in Denver (thin air) and Boston (short distance to the left field stands). He has also debunked some long-held ideas. For instance, he has shown that “corking” a wood bat by hollowing out its center doesn’t make a ball fly farther. A corked bat moves faster but is lighter, so it doesn’t deliver more force, and the wood fails to deliver a “trampoline effect” like aluminum would (see sidebar, below).
These investigations have given Nathan a high regard for players. “The way the game is played evolved over 150 years, through trial and error,” he says. “Ballplayers know how to play the game. They may not know the reason for the right way to do it,” he says, but they manage anyway. “My goal is to merely understand what’s going on.”
Now retired from the University of Illinois at Urbana-Champaign, Nathan continues to do research and consults with college and professional baseball organizations, including serving on the committee that established minimum bat weights for college baseball.
Greatest hits of physics
A baseball heats up when hit, and so does the science. Here’s what physicists have observed about the bat-ball collision.
Look ma, no hands In 2012 Cincinnati Reds player Todd Frazier (above right) hit a home run with one hand completely off the bat and the other barely touching it, showing that from a physics standpoint it doesn’t matter how (or if) a batter holds a bat.
Bat speed matters A fast swing transfers measurably more energy to a ball than a slow swing does. Each mile per hour added to the swing speed is probably worth an extra six feet on a long fly ball, after accounting for wind speed and loft.
The secret of metal Hit balls travel farther off a metal bat than a wooden one of the same weight because aluminum bats are hollow and provide a slight “trampoline effect” that returns energy to the ball.