UI conducts ‘field’ research

By Sam Johnson

Anyone who watches baseball has seen it – an infielder running back and forth, trying to get under a relatively easy infield pop-up, only to lunge back at the last second in order to make a catch.

According to physics professor Alan Nathan, some of these pop-ups may be difficult to catch because of the path they follow in the air.

“These aren’t your usual pop-ups,” Nathan said as he began talking about the different paths a baseball can take when hit.

And they aren’t.

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Nathan recently simulated a wide range of trajectories for fly balls and found that some infield pop-ups hit with a lot of backspin may be doing some pretty strange things in the air, and later wrote a paper about his findings with his colleagues.

In his calculations, Nathan highlights three special cases where pop-ups take paths with points or – in extreme cases – loops.

“In order to see these effects, you have to be able to put a lot of spin on the ball, which means you have to the hit the ball pretty hard,” said Nathan,

When a baseball is hit, the distance it travels and its path depend not only on how hard the batter hits the ball but also on the angle between the ball and the bat. If the batter hits the center of the ball with the center of his bat, the ball will fly without spin. However, if the batter, especially a strong one, severely undercuts the ball, it will have a considerable amount of backspin and could move in deceptive ways.

The different paths of a baseball are classified by the distance between the center of the ball and the center of the bat. At distances of less than 1.5 inches between the centers, a baseball takes a relativity normal path.

Once the distance between the center of the ball and the center of the bat exceeds 1.5 inches, however, the ball can take paths with points and loops.

The problem with catching these balls stems from how our eyes track moving objects.

Nathan and his colleagues used a method proposed by Seville Chapman, a physicist who also studied the physics of baseball, in his paper “Catching a Baseball.”

The method, called optical acceleration cancellation, describes how players react to pop-ups.

In his paper, Chapman wrote that if a fielder moves so that he sees the baseball moving at a constant rate, then the fielder will end up where the ball lands.

Using this method, Nathan’s group found that these baseball paths agree with professional baseball players’ movements when catching strange infield pop-ups.

Specifically in the 1.5-inch case, a fielder using this method would run back, forward and finally back again in order to catch the ball.

Former major league infielder David G. Baldwin interviewed fellow former players and found that the group’s research agrees with the players’ experiences.

“A lot of times, the backspin is going to make (the ball) carry a little farther,” said Joe Bonadonna, junior infielder for the University baseball team.

While the results of this paper are mainly theoretical, Nathan said his group will soon test their theory.

“One of the things we are going to do over the summer is use a pitching machine – instead of pitching (the ball) horizontally – to just pop (the ball) up,” Nathan said. “We are going to see if we see (these paths) occurring.”

Physics can be used to explain some of the interesting phenomenon in baseball, but Nathan said he does not think that research on the physics behind baseball has much practical application.

“Ball players know how to play the game,” Nathan said. “What I am trying to do, and what people like me are trying to do, is explain from a scientific point of view why (baseball players) do what they do.”