Ah, springtime, and young people's thoughts turn to... baseball, of course. But this column is not about "how" to throw a curveball, so you'll have to look that up on your own. Here, the focus is on the "why" of the curveball. There are two different things that cause a spinning ball to curve. One is known as the "Bernoulli effect" and the other is known as the "Magnus effect." The Bernoulli effect is the easiest to understand, so we begin with that, even though the Magnus effect is the dominant one in causing a ball to curve. (Contains 8 figures.)