Muhammad Ali’s favorite baseball pitch must be the knuckleball because it floats like a butterfly and — when batters swing and miss — it stings like a bee.
By PETE GRATHOFF
The Kansas City Star
With Boston’s Tim Wakefield scheduled to pitch against the Royals this week, it’s a good time to look at the science behind the knuckleball.
Let’s start with the grip. A pitcher presses the fingernails of his index, middle and ring fingers just below the seams of the ball. The thumb is below the ball with the pinkie off the side. However, in Wakefield’s case, he only digs the index and middle fingers into the ball and the ring finger is off to the side. It is used to grip the ball.
No matter how the ball is held, the pitcher then pushes it toward home plate instead of letting it roll off the fingers.
This limits the spin of the ball, which is ideal.
“If the ball is thrown with very little rotation, asymmetric stitch configurations can be generated that lead to large imbalances of forces and extraordinary excursions in trajectory,” Robert Adair wrote in “The Physics of Baseball.”
In other words, the ball will move quite a bit. That’s because of the stitches, which affect how the air pushes the ball.
When the ball is thrown, its surface interacts with a thin layer of air, which is known as the boundary layer. The air in the boundary layer separates from the ball, creating a wake behind it which results in air resistance known as “pressure drag.”
The ball pushes the air in the wake to one side and the air pushes back. As a result, the ball accelerates sideways and no longer moves in a straight line — much to the chagrin of the hitter.
Dave Clark, who wrote the book “The Knucklebook,” explained further how the stitches affect the pitch at his Web site on the subject ( www.oddball-mall.com/knuckleball/mego.htm).
“The action of the knuckleball, however, takes into account the fact that some stitches are moving towards the flow of air in front, and others are moving away, at a very slow speed,” Clark wrote. “The fact that the stitches move around the ball in quite a complex curve on a knuckleball and the ball may rotate at different rates in different ways causes these swirls behind the ball to change size and direction, form and disappear, and move location on the ball, producing changing locations and strengths of low pressure that really can’t be predicted.”
So the ball will experience a greater amount of movement than a fastball.
Clark also came up with a “Ferris Wheel Effect,” which may help explain the movement of the ball a little better. That is, if you’ve been on a Ferris Wheel.
“Ride one and notice that although you always face forward, the air comes at you from above as you rise up, then it shifts to the front as you reach the top, then from below as you ride down the front,” Clark wrote.
“A non-rotating knuckleball, thrown slow in a big arc, ‘sees’ the wind from slightly above the front-center, then directly in front, then slightly below front-center. This movement of the ‘relative wind’ (as skydivers call it) along the front of the ball will naturally produce shifts in where and how those stitch-produced swirls (‘vortices’) are produced and therefore how the wake is shaped and sized.
“It’s known by wind tunnel tests that only a small rotation of a knuckleball can produce a huge change in this wake, so practiced knuckleball pitchers who can keep the spin off experiment with different orientations of the ball in their hands to produce the ideal action for them personally.”
Given the way the ball moves around, you may wonder why more pitchers don’t throw the knuckleball.
Wakefield said it’s not as easy as it sounds, and that early in his career he was fortunate to learn from Charlie Hough and Tom Candiotti.
“It’s a hard pitch to throw,” Wakefield told reporters during last year’s American League Championship Series. “Not a lot of guys can do it.”
To reach Pete Grathoff, call 816-234-4330 or send e-mail to email@example.com