Photo credit: K8 Aeronautics Internet Text Book, wings.avkids.com
In honor of Roy Halliday pitching a no-hitter in his first post-season appearance, above is a photo of a spinning (backspin) baseball in a water tunnel. The K8 Aeronautics Internet Text Book has a fantastic explanation of the physics behind the deadly curve ball. They write:
A pitcher makes a finger snapping, wrist twisting movement as the ball is released. This creates a topspin of the ball as it travels, so that the top of the ball is moving forward against the air and meeting resistance while the lower half is spinning backward and moving in the same direction as the air. The air pressure above the ball is greater than the pressure below, causing the ball to curve downward. In the 60 foot 6 inch distance between major league pitcher and batter, this curving force can move a ball down a foot or more.
Read more about curve balls -- including a breakdown of what's behind a "slider" and a "sinker" at The K8AIT Web page