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Science Friday: Curveball Physics

Submitted by Tjadendevries on Fri, 04/29/2011 - 2:19pm


thrown for a curve

    Over at Wired, David Dobbs has a very nice post on famed pitcher Sandy Koufax -- excuse me, "the greatest pitcher ever" -- and the curve ball, a nasty (if you're the batter) trick whereby the baseball dives downward suddenly just before it reaches the plate, faking out the batter. It's fast, too, traveling at least 75 mph and spinning at an angle of around 1500 rpm. It only takes about 0.6 seconds to get from pitcher's hand to home plate -- not a lot of time to react. David's post focuses on the perceptual illusion created as the ball travels towards the batter, and it's that optical illusion that makes the curve ball so bloody hard to hit.

    Or, as the decidedly salty Mickey Mantle said after being struck out by one of Koufax's infamous curve balls in the 1963 World Series: "How the fuck is anybody supposed to hit that shit?" How indeed? I'll let David explain what's going on perceptually:

      [T]he curveball kills you two ways: first, through actual movement; and second, through an extra perceived movement — illusory — that further complicates the task of getting the tiny strip of sweet spot on your bat onto the ball.

      The extra perceived movement rises from a difference between the neural dynamics of central vision and those of peripheral vision. This effect of this difference is that a baseball that is rotating horizontally but falling straight down as it comes toward you will appear to fall vertically if you’re looking straight at it — but appear to move sideways if it’s in your peripheral vision. ... This in turn happens because your eyes simply can’t keep up with a pitch as it approaches you and effectively accelerates its path across your field of vision. The ball goes from moving at you to moving past you. At the crucial moment — the last few feet of the ball’s half-second, 60-foot trip to the plate — you must of necessity switch from seeing the ball with your central vision to seeing it with your peripheral vision.

      To add to your troubles, it is in this tenth of a second or so that the curveball also moves the most in reality. ... So just as the ball’s real downward and sideways motion is greatest, the curve’s apparent break is exaggerated by visual dynamics.

    [...]

A lot more at the link

http://twistedphysics.typepad.com/cocktail_party_physics/2011/04/throwing-a-curve.html