A knuckleball is famously difficult to throw, hit and catch because of its erratic behavior. It seems to fly through the air with no spin and then break suddenly in any direction. The ball’s seams are key to this behavior. Not just tools to keep the leather together or leave impressive welts when you “catch” a ball with your shin, the seams affect the airflow around the ball.Dickey's speed on his knuckleball is amazing. However, he was having some difficulty controlling it against the Yankees on Sunday. I enjoyed listening to Terry Francona answer a question about when Wakefield would have a game when his knuckleball wasn't unhittable. Francona said that he could be unhittable for four innings, then get pounded in the fifth, then be unhittable for two more innings. That is part of the frustration of the pitch. It can all of the sudden become meat. That tempermental nature makes Dickey's streak so much more impressive.
Air drags along the smooth parts of a baseball surface, but the seams produce little vortices that allow air to travel more quickly over them. A fastball rotates 16 or 17 times between the pitcher and batter, and the rapid rotation means that the airflow turbulence caused by the seams is pretty evenly spread over the whole ball and the entire trajectory of the throw, so it travels steadily. On the other hand, a knuckleball rotates only one half to one time on its way to the batter, so the airflow turbulence stays on one side of the ball for a while before slowly moving to the other. The ball drifts in the direction of the leading seam, which slowly moves from one side to the other.
Slow is, of course, relative when it comes to pitching. Most knuckleballs poke along at a zesty 65 to 70 miles per hour, although Dickey’s have averaged 77 mph this season. By comparison, fastballs in the majors average about 90 mph. Dickey’s speed may be part of the secret to his success, especially when it comes to his unusually high strikeout percentage. Higher speeds mean less erratic movement, which helps him stay in the strike zone.
Tuesday, June 26, 2012
The Physics of the Knuckleball
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I STILL think the big variable is the nature of the air between the pitcher's mound and home plate. I came to this conclusion watching my model airplanes land. The air near the ground is usually jumbled and this increases with the temperature. A pitch travels over grass (cool) and then dirt (hot) which is just about where the action really starts. If I were a manger and had knuckleballers on my staff, I would always pitch them on hot afternoon games—they're freaking unhittable under those conditions.
ReplyDeleteThat seems like a reasonable hypothesis to me. I definitely saw different effects on different days when throwing the thing. Some days it didn't seem to move a whole lot and it still wasn't getting hit, and some days it was moving a lot but it seemed to break right to the sweet spot on the bat.
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