Physics of Baseball and Softball


Physics of Baseball and Softball
, 
Rod 
 
 Cross
 Springer, New York, 2011. $169.00 (323 pp.). ISBN 978-1-4419-8112-7



I was intrigued when I learned Rod Cross had written a book called Physics of Baseball and Softball. Originally a plasma physicist, Cross has in the past 15 years authored about 40 articles on the physics of sports, particularly tennis (see his Quick Study in PHYSICS TODAY, September 2008, page 84 ). Cross’s articles provide a penetrating analysis of what actually happens when striking implements meet balls and when balls bounce on turf or other court or stadium surfaces. He has an obvious affection for tennis: In his 2002 book with Howard Brody and Crawford Lindsey, The Physics and Technology of Tennis (Racquet Tech Publications), he displayed a deep appreciation for that game from a player’s perspective.

But here’s the rub: Cross is Australian, not American. Does this mean we Yanks must now suffer the ignominy of having the best book on baseball physics written by an Australian? Will Cross’s book forever supplant Yale professor Robert Adair’s Physics of Baseball (3rd edition, Harper-Collins, 2002) as the go-to source on this subject?

The answer is yes and no. The “yes” is that Physics of Baseball and Softball does provide the clearest and most extensive explanation of what happens the instant bat meets ball. That instant occupies 13 of the book’s 18 chapters—all but the introductory chapter on the basic physics, two chapters on the trajectories of batted and pitched balls, and two on the mechanics of throwing a ball and swinging a bat. The “bat-meets-ball” chapters include discussions on the physical properties of bats and balls, hysteresis effects when balls are deformed repeatedly, the most favorable parameters for modeling bat–ball collisions, how to measure and parameterize bat performance, how bat vibrations affect energy losses, the various definitions of a bat’s sweet spot, and whether flexible bat handles improve or impair performance. Even as he presents the technical arguments, Cross takes pains to explain the issues so that a motivated nonphysicist could follow the explanations. The final chapter outlines a series of elementary projects investigating bat and ball properties and interactions. It could serve as the basis for laboratory experiments in an introductory physics course.

Several issues concerning bat performance that were largely unresolved only two decades ago should be laid to rest in Physics of Baseball and Softball. One puzzle was whether the moving mass of the batter’s arms affects momentum transfer. It does not, because bat–ball collision times are so short that the elastic waves set up in the bat reach the batter only after the ball is long gone. Another issue surrounded the question, What is the best definition of the sweet spot? It is the contact point that minimizes bat vibrations. Yet another enigma revolved around whether there is a single contact point on the bat that maximizes ball exit speed—there is not; it depends on bat speed and pitch speed.

So is this the last word on the physics of baseball and softball? No, it is not. The book is not really about the sport of baseball or softball. Rather, it is a treatise on bats and balls and on batting balls. The culture and history of baseball and softball are mostly absent. There are no pictures of people playing baseball and professional players are barely mentioned. There are no discussions of kinesiology, training, stadium effects, helmet design, famous games, predicting future performance, or strategy. Rod Cross is no Bill James.

Cross obviously loves sports and physics, but apparently isn’t afflicted by that deep and often troubled relationship with baseball that haunts many of us. From reading the book, I suspect Cross has never struck out to end a game, lost a fly ball in the Sun, or thrown 100 batting-practice pitches to a Little Leaguer. I doubt if his emotional equilibrium has ever been destroyed by a win—or loss—by the New York Yankees or [your favorite team name here] or by the trade of a particular player. Physics of Baseball and Softball is good at what it does, but one thing it doesn’t do is communicate a love of the game. In that respect it differs from Cross’s book about tennis, Adair’s book about baseball, and other recent sports physics books, such as Trevor Lipscombe’s The Physics of Rugby (Nottingham U. Press, 2009) and John Kimball’s The Physics of Sailing (CRC Press, 2010).

Unfortunately, Cross’s book is expensive, too. The $169 list price will discourage its purchase by most sports fans and many academics. It’s true, as the author’s website notes, that $169 is about half the cost of a good bat. And I must admit to occasionally spending more than $169 for two good seats at some Major League stadiums. So invest in this book if you care about how baseball bats work or want to teach undergraduates about it. But if you want a book that also celebrates your love of the game, this isn’t it.