Physics can explain the fastball’s unexpected twist, new study finds

Enlarge / Los Angeles Dodgers pitcher Clayton Kershaw delivers the pitch during the first inning against the Boston Red Sox in Game Five of the 2018 World Series at Dodger Stadium. (credit: Sean M. Haffey/Getty Images)

The fastball is, as its name implies, the fastest pitch in major league baseball, reaching speeds in excess of 100 MPH, and ideally arriving at the strike zone before the batter can react. Sometimes those fastballs make an unexpected twist that can make or break the outcome of a game. What accounts for differences between pitches? It all comes down to spin speed, spin axis, and the orientation of the ball.

So says Barton Smith, a mechanical and aerospace engineer (and staunch baseball fan) at Utah State University. He studies the complicated physics of how a pitcher's biomechanics can influence the air dynamics of a baseball. Smith presented his findings earlier this week at a meeting of the American Physical Society's Division of Fluid Dynamics in Atlanta, Georgia.

There's some colorful history to the study of baseball pitches, most notably the heated debate in the 1940s and 1950s around whether a curve ball really does curve, or whether it's just a trick of perception. St. Louis Cardinals pitcher Dizzy Dean had this to say to skeptics: "Ball can't curve? Shucks, get behind a tree and I'll hit you with an optical illusion." Dean was right. Curve balls really curve-and we know why in part because of research in the 1950s by Lyman Briggs, a former director of the National Bureau of Standards (now the National Institute of Standards and Technology in Gaithersburg, MD).

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