Spin is in. Stars spin around supermassive black holes. Planets spin in orbit around the sun. Earth spins daily on its axis, a toy top spins on a desktop, atoms spin, quarks spin, electrons spin and even nonmaterial photons spin. Spin is important in innumerable interactions in the universe, not the least of which is baseball.
Spin has been a factor in baseball since 1867/1870 when Candy Cummings/Fred Goldsmith demonstrated the first curveball.
For more than a century, baseball players, coaches, scientists, aficionados and pundits disagreed about whether a thrown ball could actually curve.
Scientists thought that the ball was too heavy and air resistance too weak to have any significant effect on the ball’s trajectory. Baseball people said they saw it curve; many others said it was an illusion.
Hall of Fame pitcher Dizzy Dean famously quipped, “Go stand behind a tree 60 feet away, and I will whoop you with an illusion!”
Perception is important when you have a 5-ounce, 2-inch circle coming at you at a hundred miles an hour and it is spinning one way or another. You would have less than half a second from the time the ball leaves the pitcher’s hand until it whooshes over home plate, and depending on the pitch, that time could be longer by as much as 20 percent.
Batters facing a ball that takes anywhere from 400 to 500 milliseconds to arrive cannot analyze its path. They expect a smooth trajectory based on an instinctual knowledge of how gravity works.
Baseball players have a highly developed eye, and it is likely that those who claim that a curveball does not curve truly cannot see it. Modern pitch-tracing technology that the major leagues use during games makes the variety of smooth but “warped” trajectories visible.
Flinging a baseball at twice the speed that the best of the rest of us could ever muster is impressive. Putting it consistently through an imaginary 1-1/2-by-3-foot box 60 feet away is striking.
Add to that an infinite variety of wrist and finger actions at just the right split millisecond and you have a breaking ball.
All breaking balls share a common physics. Aerodynamic forces that curve a 5-ounce baseball also lift a 1.4 million-pound Airbus 380 because as speeds increase upward of 60 mph, thin air becomes quite viscous and behaves more like a thin liquid.
Like a spinning tire flinging sand on the beach, a spinning ball carries air before flinging it off. The farther around the air goes, the more forcefully the ball pushes it away.
Conversely, the air exerts an equal but opposite force on the ball. This force, the Magnus force, is perpendicular to the spin axis and in the direction that the front of the ball is spinning.
The direction of Magnus force on the ball is the direction it will deflect up/down and right/left relative to gravity’s theoretical trajectory.
On a baseball with medium seams, the Magnus force can be up to one-third the weight of a 60-80 mph ball spinning at 2,150 rpm.
Yet, there is more to pitching than painting the strike zone with a spinning ball. The goal is fooling batters, and the best pitchers have a gut instinct about how much spin, where and when. There is a magical quality about a good pitcher spinning in his groove.
Richard Brill is a professor of science at Honolulu Community College. His column runs of the first and third Friday of the month. Email questions and comments to brill@hawaii.edu.
