All in the Wrist?

Aerios: concerning the air.  Dynamics: force.  The Ancient Greeks coined the term aerodynamics for their study of forces and the resulting motion of objects through air.  Today, all the attention a pitcher pays to the placement of his fingers in relation to the seams is done to take advantage of the aerodynamic properties of a ball in flight.  Because the seams are the only raised portion of the ball, a baseball made to spin as it moves alternates its smooth and raised surfaces. The cowhide – cut in two peanut-shapes – is smooth. The 216 stitches used to hold the cowhide together, a raised saddle pattern, or double horseshoes, on the ball.  These smooth and raised surfaces are the cause of the ball’s performance as it responds to the effects of Lift, Thrust, Drag, and Gravity.

Daniel Bernoulli’s work with fluid mechanics in the 1700’s provides the basis for many of the concepts used in the study of aerodynamics today.  According to Bernoulli, an increase in the speed of the fluid occurs in concert with a decrease in pressure or a decrease in the fluid’s gravitational potential energy.  That’s why, for a baseball, it’s not only the accuracy and strength of a pitcher’s arm that decides the ball’s path.  It’s also the orientation of the stitches as the ball moves through the atmosphere.

But a baseball doesn’t create aerodynamic forces in the same way as the wing on an airplane or other airfoil. The spinning of the ball and the raised surface of the stitches create a whirlpool of rotating air around the ball. This exerts pressure and the ball moves in the direction of least resistance. This Magnus Force is what causes a perfect curve ball to curve right at the plate as the disequilibrium reaches it’s maximum at the end of it’s seconds-long, sixty feet six inch journey.

A successful pitcher knows how to use his arm and wrist to optimal effect.  He also knows throwing the ball with the proper speed and arm movement isn’t enough.  If his fingers aren’t positioned correctly, there’s no way he can count on the ball to cross the plate where he wants. It all comes down to where he positions his fingers on the ball.

Throwing a curveball?  The index and middle fingers are positioned so the middle finger is on the right horseshoe seam with the index finger between the seams. It’s released with the wrist angled so the thumb is on top to give the ball a downward spin – top to bottom. With the right flick of the wrist and a pitch speed of 70 mph or more the ball will curve just as it reaches the batter.  How much it curves is determined by the extent of the disequilibrium created by the seams as the ball spins on the way to the plate.  If a righty pitcher facing a righty batter wants a big break to the outside, he’ll create a large area of disequilibrium by orienting the ball so four of the seams are rotating toward the batter on the way to the plate.  If he requires a smaller curve, he’ll orient the ball so only two seams rotate toward the batter.

For the four-seam fastball essential to the arsenal of every Major League pitcher, the index and middle finger are placed across one side of the horseshoe portion of the seam as it’s thrown at full velocity.  The ball rotates bottom to top.

Prefer a Slider?   That’s thrown with the index and middle finger close together and off-center as they run down the length of a horseshoe portion of the seam.  The tight spin apes the fastball but it has a striking late break down and away when thrown by a righty pitcher to a righty batter.  The pitcher creates the spin with a downward pull at release but the aerodynamics of the seams – not the action of the wrist – causes the spin. It’s the off-center spin that causes the ball to break.

You don’t see many Knuckleballs.  They’re difficult to learn, locate — and hit!  The pitcher puts the tips of both his index and middle fingers on one side of the narrow portion of the seam. He uses his thumb on the bottom of the ball to form the secure grip he needs to hurl the ball. The Knuckler is pushed straight out at release, with as little spin as possible. Because there’s virtually no spin, the wind pushes the ball around on its way to the plate.

Want to know more?

In 1987 President of the National Baseball League, Bart Giamatti, named Dr. Robert K. Adair Physicist to the National League.  Adair’s wonderful book, The Physics of Baseball, resulted. Its detailed scientific and conversational explanations cover the effect of factors ranging from the length of time a batter has to reach a decision on a pitch and what a pitcher can do to minimize that time, to the optimal weight of a bat. Adair is definitely a guy who believes in making the complex simple. It’s not quite as simple as “simple,” but it is on the right track!


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