[hotreds]

Did you ever wonder how a pitcher can throw a ball that can almost magically drop sharply before reaching the plate? This ordinary phenomenon is called a curve ball, and the explanation of this occurance can be described with a few basic lessons in fluid flow dynamics.

What you have to remember in this problem is that air is a fluid, and that things moving through air behave much like those passing through water, only on a less noticeable scale. An observable phenomenon known as the Venturi Effect tells us that a fluid flowing at a higher velocity has a lower pressure than that same material at a lower velocity, all other variables kept constant. To observe this, suspend two tennis balls from equal lenth strings about 5 cm apart. Blow a hairdyer though the gap between them and they will actually be drawn together because atmospheric pressure will try to fill the low pressure void and will in the process push the balls together. So high velocity means low pressure.

Back to the ball. The pitcher throws the ball with plenty of topspin (or, to make it curve left or right, sidespin). The spin of the ball magnifies the velocity of the air passing below the ball and lessens the velocity of the passing air above the ball. Higher velocity below and lower velocity above means low pressure on bottom and high pressure on top. The high pressure takes advantage of the low pressure and forces the ball to travel downwards.