beach mountain
It's a Breeze - How Air Pressure Affects You

Earth Science Spin

Earth science isn't commonly associated with America's favorite pastime, but the earth, and its atmosphere have a great effect on the way baseball is played. There are the obvious conditions that affect a game such as the surface the game is played on, the location of the stadium and the wind speed. But there are other, not so obvious factors, like the drag of the air on the ball after it is thrown.

Most people know that a curveball is a very hard pitch to hit, but don't actually know how or why the ball curves as it does. The actual break of the ball depends on the speed of the pitch, its rate of spin, and the direction that the ball spins. For example, a four-seam fastball is thrown with backspin, allowing all four seams on the baseball to catch the air and generate a small amount of lift.

The curveball is greatly affected by the stress put on it by the air. When a curveball is thrown, the pitcher snaps their wrist like they were turning a doorknob, spinning the ball in the same direction that they are throwing. The stitching of the ball catches the air, but now it creates higher air pressure towards the bottom of the ball instead of the top. The higher air pressure forces the air away from the ball's surface, while the air at the top of the ball is able to hang onto the ball's surface for longer. The difference in pressure pushes the ball downwards, creating a quick drop at the end of the pitch!

So the next time you watch a big leaguer throw a curve think about how the air is affecting its spin, and how earth science affects the game of baseball!


Updated: January 22, 2003