Physics of a curveball

When the Texas Rangers were in the World Series again, I thought about the physics of pitching curveballs. If you know the science behind it, you probably don’t pitch better curveballs, but it’s interesting to know why the ball moves the way it does. But who knows, maybe it does. Let me know if it actually helps to improve your pitching.

The most important characteristic of a curveball is the spin of the baseball. The spin makes it easier for the air to pass on one side versus the other when the baseball is thrown. This is because the surface of the ball is not absolutely smooth; it’s rough on a microscopic scale. Due to the surface’s roughness, the ball pushes surrounding air with its spin movement. The result is that the air passes the ball faster on one side than on the other. This leads to an area of reduced air pressure on the side of the ball where the air passes faster. In physics, this is called Bernoulli’s principle in general, and Magnus effect if it applies to spinning objects. The ball is dragged to the side with the lower air pressure, so that it curves in this direction. The picture below of a forward-moving baseball with a spin should help you visualize these facts. (The ball in the picture curves to the right.)

A baseball in flight, thrown with a spin.

Another physics law regarding angular momentum preservation guarantees that once the ball has left the pitcher’s hand, its spin is preserved so that the ball is constantly dragged in only one direction.

Play ball!