This is perhaps the hardest pitch to master. Not just for a pitcher,
but for an aerodynamicist as well. Some believe that a knuckleball
thrown without any spin will be at the mercy of any passing breeze. An
thus, dances through the air in an unpredictable fashion. However, the
most likely reason for the "dance" of a knuckleball is a very
slow spin. Researchers have learned that a slight change in the
orientation of the ball with respect to the flow of air results in
dramatic changes in the forces acting on the ball. Not only does the
magnitude of the force change, but the direction also changes. This is
why the ball appears to "dance".
The mechanism by which the forces change magnitude and direction is not
known. However, one can theorize that the stitches play a key role. The
stitches will most likely cause the boundary layer to trip to a turbulent
state. As we know, turbulent flow will stay attached longer than laminar
flow. In fact, once the boundary layer becomes turbulent, a separated
flow tends to reattach. This reattachment will dramatically alter the
forces on the ball. Similarly, as the ball rotates, a region that was
turbulent due to the position of the stitches, might now become laminar.
The laminar flow will separate earlier than the turbulent flow. This
altering of the state of the flow from laminar to turbulent, separated to
attached, would cause the forces on the ball to fluctuate as shown by the
Furthermore, it is important to note that even if the pitcher throws the
ball with no rotation, the flow asymmetry will cause the ball to rotate.
The flow asymmetry is developed by the stitch pattern on a baseball.
The Spitball and the Vaseline ball
As previously mentioned, the knuckleball is very difficult for a pitcher
to learn much less control. A simpler and more effective method is to use
a lubricant such as saliva or vaseline. This causes the pitch to slide
through the fingers and thus have little spin. Therefore, the ball moves
like a knuckleball, but at the speeds of a fastball. This makes a
spitball next to impossible to hit.
Other dirty tricks employed by pitchers involve scuffing the surface
and/or polishing the surface. Just as a rough surface promotes turbulent
and, therefore, attached flow, a polished surface will maintain laminar
flow and hence separated flow. By roughening one side and polishing
another, the effects of various pitches will be exaggerated. So, in
reality, a pitcher is not just a ball player, but an amateur
aerodynamicist as well.
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Last modified: Sat May 23 10:39:08 PDT 1998
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