Here we go...http://www.msnbc.msn.com/id/5086320/default.asp
Why hitting curveballs scores more homers
By SHARON BEGLEY
With Memorial Day upon us, scientists' thoughts turn to summer sports, and what could be more summer-y than Frisbee and baseball?
Conventional wisdom in baseball holds that, everything else (such as the speed of the bat and how solidly it connects) being equal, a fastball is more likely to be smacked for a home run than a curveball is. But when University of California, Davis, engineering professor Mont Hubbard and his colleagues modeled all the forces on a batted ball, they found that, in baseball as in politics, it's the spin that matters _ and conventional wisdom, in this case at least, is wrong.
When a curveball leaves the pitcher's fingers it has topspin, which means the top of the ball rotates in the direction of flight (toward the plate). Fastballs, in contrast, have backspin, with the bottom of the ball rotating in the direction of flight. Topspin causes a ball to experience a downward force, because the rotation changes the distribution of air pressure around the ball so there is more pressing down on the ball than up. Hence curveballs' habit of suddenly plunging, to batters' dismay. Backspin, in contrast, generates an upward force, somewhat like the one that keeps an airplane aloft, which is why a fastball rises unless the pitcher gives it a countervailing spin.
When the bat makes contact, the most obvious thing it does is reverse the ball's direction, so it heads toward the field rather than the plate. But contact also changes the ball's spin. Assuming good contact in each case, a fastball that arrived with backspin therefore leaves with topspin, while a curveball arriving with topspin leaves with additional backspin and thus more home run potential.
"A curveball already has batted backspin," says Prof. Hubbard. "With a fastball, in order to give it backspin and let it benefit from aerodynamics, you have to reverse the spin," which is tough to do. The well-hit curveball heads for the field with more of the kind of spin that gives it fence-clearing lift and distance.