SABR

Using Infrared Technology at the World Series

From SABR member Alan Nathan (chair emeritus of our Science of Baseball Committee) at The Physics of Baseball on October 20, 2011:

At Game #1 of the 2011 World Series, Fox experimented with an infrared (IR) camera, that produces a "heat map" as its image. With such a camera, bright spots are hot and dark spots are cool, relatively speaking. As it turns out, in the 9th inning of that game, an event occurred that showed the potential value of this technology. Adrian Beltre hit a ball nearly straight down into the batter's box; it subsequently bounced to 3B and Beltre was thrown out. Both Beltre and the announcers thought the ball actually hit Beltre in the foot, which would have been a foul ball. The umpire didn't see it that was and Beltre was ruled out on the ground ball.

Now take a look at this link and be sure to watch the video replay of the broadcast, including the IR clip at the end. There is a lot of interesting physics in the IR clip. As Yogi once pointed out, you can observe a lot by watching. So watch the clip, then return here for some explanations of what you saw.

1. Note how the ball heats up upon contact. That is largely due to the friction of the strands of yarn rubbing together as the ball compresses, then expands back to its normal shape during the collision. That process is inherently inefficient and much of the initial energy is dissipated by the friction, resulting in the interior of the ball heating up. That effect is clearly visible with the IR camera. The loss of energy due to the heating up of the ball is what results in a "coefficient of restitution" (COR) of the ball that is less than 1 (more like 0.5, meaning about 75% of the available energy is lost). The COR characterizes the "bounciness" of the ball. In fact, a baseball is not very bouncy. If a baseball were a superball, with a COR close to 1, then we probably would not have seen the ball light up nearly as much. But, read on for another reason for the ball to light up.