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    Porter W. Johnson and the Physics of Baseball

    Fall 2003

    By Brian Grow

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    Like a utility player on a baseball team, Physics Professor Porter W. Johnson has done just about everything in his 34 years at IIT.

    He has taught, consulted and chaired three different IIT departments. He has published 72 scientific papers on topics from Tullio Regge amplitudes to quark masses. He has promoted science and math in Chicago-area high schools and encouraged teachers to add more science to their curriculums. And now, he is finishing the third part of a four-part book series on Quantum Field Theory.

    But perhaps Johnson’s most unique contribution to physics and IIT derives from a different passion—his love of baseball. The physics of baseball, that is.

    Since his earliest days growing up in Chattanooga, Tennessee, Johnson says he’s been fascinated by America’s national pastime: its larger-than-life heroes such as Babe Ruth and Joe DiMaggio; its panoply of statistics; and the scientific challenge of understanding baseball’s mental and physical interaction.

    That passion grew out of the days when, as a young man, Johnson and friends were members of the Knothole Gang—named after kids who watched minor league baseball games through knot holes in the outfield fence. He and Chattanooga chums used to attend local Southern League games of their minor league team, the Lookouts. And it was there that Johnson first had an inkling that the science of baseball was going to be part of his academic life. “As a player, I was never that great,” he says. “But I realized that I looked at the game from a different perspective: the perspective of a scientist.”

    Since then, baseball has become a cornerstone of Johnson’s teaching and made him one of the foremost speakers and analysts on the physics of baseball. He has commented for newspapers and television, including recent chats with Chicago’s WGN and NBC channels on the Sammy Sosa corked bat controversy. “I’m sure he made a mistake,” says Johnson. But like a true scientist, he still gets excited explaining how a corked bat may be just as strong as a normal bat, but because it is lighter, a player can swing it faster.

    What’s more, he likes to quote a line from the famous baseball movie "Bull Durham" to explain how the sport can be applied to science: “Baseball requires nonlinear thinking.” Rather than just marveling at the inexplicable skills of baseball players, that belief leads Johnson to ask questions like: How does a batter hit Randy Johnson’s 96-mile per hour fastball? How does Sammy Sosa hit so many home runs? Why does the baseball fly farther in high altitude stadiums such as Denver? How did Willie Mays judge the trajectory of a fly ball?

    Here’s one example of Johnson’s answers:

    “The major league pitcher stands on the mound a distance somewhat less than 20 meters from the batter’s box, and throws fastballs at a speed somewhat greater than 40 meters per second, so that the entire trip takes place in 0.4 to 0.5 seconds. The batter must decide in that brief instant whether, when, where and how to swing. Because of the influence of gravity, the baseball drops significantly from a projected straight-line path during its travel. The distance dropped is given by: d = 1/2gt2 = 1.2 meters … It is remarkable to me as a scientist that the batter can hit such a thrown baseball. Certainly, a person off the street would have trouble even seeing a major league fastball, although a significant ‘hum’ could be heard as it whizzes by!”

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