"This is a funny business.."

Baseball centers around the (seemingly) eternal struggle between pitcher and batter, and each uses physics, albeit intuitively, to gain a slim advantage over the other in determining the fate of the game's center of interest -- the ball.


It all revolves around the ball

Alvin Morman
Alvin Morman caption

When you pick up a baseball, it immediately suggests its purpose: to be thrown fast and with considerable accuracy. The pitcher, with his dance-like windup, prepares to do exactly that by transferring momentum from his body to the ball. To appreciate why this is necessary, try throwing a ball without moving your feet; it's difficult to throw it very far or very hard, but a forward step makes throwing much easier. So during the windup, the pitcher moves his entire body weight back behind the pitching rubber. Then he thrusts it forward to deliver the pitch.

This transfer of momentum from body to ball involves a biomechanical principle called sequential summation of movement. According to this principle, the largest body masses move first, followed by progressively smaller ones, in much the same way a multi-stage booster rocket jettisons a satellite into space: the large booster starts the process, is jettisoned, then is followed by the burning and jettisoning of progressively smaller and faster stages, until finally the small satellite is released at high speed. In baseball, the pitcher drives first with his legs, then his hips, shoulders, arm, wrist and fingers. As each part approaches full extension, the next part in the sequence begins to move, efficiently transferring momentum in a whip-like action. Proper timing is necessary to produce speed and accuracy, and to avoid strain and injury.

A pitcher's body rotates around the foot he keeps planted firmly on the mound. The ball, held overhead in his extended arm, is like a rock whirling on the end of a string. Just as a twirling rock on a long string has more angular momentum than the same rock on a short string (that is, it's more likely to travel farther and faster), the ball in the hands of a tall pitcher can be launched with more speed. (Fastball pitchers are traditionally lanky fellows.) And since the pitcher actually steps downhill, moving off the crest of the mound as he throws the ball, the height of the mound also affects the force of the pitch.