The Physics of Debunking the Amazing Batting Trick

In addition to being a fabulous source of solid information, the internet is also chock full of fakery and deception. I think most of us are okay with this sort of duplicity if it is harmless enough. Below is a video that has been kicking around for about a decade. It is entertaining to watch and to think about, so enjoy.

There is little doubt this was done with some form of trick photography. After all, even a professional ballplayer can’t hit a ball with the accuracy required to make this happen. The precision needed is simply beyond human abilities. Still, it is fun to watch.

The four devices used to reflect the ball are usually called “Pitch-Backs.” I recall getting my first Pitch-Back as a kid. I tore it out of the box, set it up on the lawn, and began imitating my hero, Sandy Koufax – never mind that while I was born a lefty, they converted me to a righty in school, further reducing my chances of making it as a ballplayer.

The right-handed Koufax-to-be fired the ball and immediately noticed that the return off the Pitch-Back was much slower than the fastball I fired at it. In fact, the ball bounced before it even got back to me. I should have realized right then I was more of a physicist than a ballplayer. Since I didn’t even know what a physicist was, I held on to my big-league dreams.

Almost every time a macroscopic object bounces off another object, some of the kinetic energy is lost. This type of collision is called “inelastic.” Yet, the single most important law of physics is the Law of Conservation of Energy which states, “Energy can change from one form to another, but the total energy of an isolated system never changes.”

So, what gives? The ball bouncing off the Pitch-Back clearly has less kinetic energy than it did before it came in. What happens to the energy lost by the ball? According to the law, it has to show up somewhere.

The missing energy is turned primarily into heat as the elastic bands of the Pitch-Back expand and contract. So, as the kinetic energy drops, the heat increases, keeping the total energy fixed as demanded by law. While the resulting change in temperature of the Pitch-Back is very hard to detect, you can see the effect in a common rubber band.

Put the rubber band next to your cheek to get a sense of the initial temperature (your cheek is particularly sensitive). Now, stretch the rubber band and let it relax 20 or 30 times. Put it against your cheek again and you’ll sense that it has warmed up a bit.

You might note that major league baseballs also convert energy to heat when they collide with bats and other things as well. In fact, the amount of energy converted to heat is specified by the league. Well, they’re not physicists, so they don’t actually specify the heat.

Instead, MLB specifications require all baseballs be manufactured in such a way that any randomly selected ball will pass the following test: if the ball is fired at a wall of ash at 60 mph, it must bounce off with a speed between 30.8 mph and 34.7 mph. This is nearly equivalent to specifying the heat produced in the collision.

The speed of the ball drops by about half. Since the kinetic energy depends upon the speed squared, it will drop to about one-quarter of the initial amount. That means about 75 percent of the initial kinetic energy of the ball will be converted to heat.

If we assume that about half of this heat goes into the ash wall and half goes into the ball, I estimate the temperature of the ball would  increase only about 0.2˚F. It is generally true that even large conversions of kinetic energy produce only small amounts of heat. That’s why rubbing your hands together might heat your hands, but it won’t heat your living room.

It would be pretty challenging to measure temperature differences of 0.2˚F, but not impossible. In fact, Fox Sports did just that during the 2011 World Series by using an infrared camera. A video of a ball hit by Albert Pujols is shown below.

You can see the white spot that shows the heat produced when the ball and bat collide. You’ll notice some of the heat stays on the bat and some is carried away with the ball. This play was disputed. Pujols, with the ball in fair territory, ran toward first and was awarded the bag. The Giants claimed the ball was fouled off his foot. At the end of the video, is there evidence the ball struck his shoe? I think so, but you decide.

How did we get from a questionable YouTube video to the World Series? No wonder we professors have a reputation for rambling off topic. Let’s return to my backyard pitching practice, I was whining about the ball bouncing before it reached me on the return. I quickly realized that I could tilt the Pitch-Back backward so that the ball’s launch angle on the return was distinctly higher than the angle it came in. Now, I could catch the ball before it hit the ground.

Back then, I was not a trained physicist, or I would have measured the incoming speed of the ball and the outgoing speed of the ball. Now that I am a trained physicist and can take the measurements, I don’t have a Pitch-Back or even a reasonable fastball – such is life. Nonetheless, I would estimate the ball comes off the Pitch-Back at around two-thirds of the incoming speed.

The Amazing Batting Trick uses four Pitch-Backs. So, if each of the four Pitch-Backs reduces the speed by two-thirds – check my math – I get the ball heading back toward the batter will be going at about 20 percent of the speed he originally hit it. That is a dramatic difference and should be easily seen in the video. Since the ball doesn’t appear to slow in the slightest during its travels, the video is clearly faked somehow. Still, it is still pretty entertaining – just don’t take it too seriously.