To Eli Rosenberg, the intricacies of baseball extend beyond the baseball field and spill over to another field – the field of physics.

“Basic physics ideas are important in understanding why baseballs behave the way that they do,” Rosenberg said.

Rosenberg, professor of physics and the chair of the department of physics and astronomy at Iowa State, gave a lecture entitled “The Physics of Baseball” on Nov. 14 in the Sun Room of the Memorial Union. The lecture was part of the College of Liberal Arts and Sciences Fall 2007 Dean’s Lecture Series.

Rosenberg believes baseball is simple for fans who understand the game, but sometimes they overlook the underlying circumstances that a physicist would see.

“You throw the ball, you hit the ball, you catch the ball,” he said. “That’s the summary of baseball to an outsider looking in. It’s different from a physicist’s standpoint.”

Rosenberg explained that the ball’s flight path is governed by Newton’s three laws of motion, but numerous forces act on the ball to affect its path. Some examples include gravity, the smoothness of the surface of the ball, the stitches on the ball, the rotation of the ball, the speed that it was released at and the density of the air.

The rotation of the ball, for example, depends on the pitcher’s grip, how hard the ball was thrown and the angle at which it was thrown. The pitcher’s grip, in turn, depends on several factors – a scuffed or doctored ball allows for a better grip than a smooth ball, and the stitches also help the pitcher get a good grip, Rosenberg said.

Potential hindering forces that alter the path of the ball are gravity and the density of the air. Air density affects the air resistance, or “drag force”, on the ball, which can slow a pitch by up to 8 mph by the time it gets to the plate. While air density affects the ball’s speed, gravity alters the ball’s direction.

“Gravity is a force that pushes the ball down. In fact, for a major league fastball, from the time the ball leaves the pitcher’s hand to when it reaches the plate, it’s going to drop three feet just because gravity is acting on it,” he said. “If you were to try and play with baseball physics on Jupiter, the ball would maybe go three inches, and you could build lots of smaller ballparks.”

In addition to the physics of pitching, Rosenberg explained the physics of hitting. When the bat collides with the ball – at the “point of percussion” – the bat bends and vibrates while the ball distorts. After the energy has been transferred, the bat acts as a trampoline and the ball is launched from the bat. The “sweet spot,” which is located about four inches from the larger end of the bat, is the optimal spot for energy transfer.

Rosenberg said that choosing the right bat is a trade-off between bat speed and the size of the sweet spot. Larger bats naturally have larger sweet spots, but smaller bats allow players to swing faster. To generate the maximum possible bat speed, Rosenberg said that hitters would need to use a 15-ounce bat, but a bat that light would only be 15 inches long and would not launch the ball very far.

“No ballplayer in the world is going to go to the plate with a bat that’s only 15 inches long,” he said. “The bigger the mass of the bat is, the better the situation. The problem is, the bigger the bat gets, you need to compensate with more bat speed.”

Rosenberg also discussed why the physics of baseball is not very well studied compared to other sports.

“When you look at the study of baseball, you’ll see that there are a lot more studies being done in sports like golf and tennis,” he said. “In golf and tennis, there is a lot more latitude to what you can do [with sports equipment]. In baseball, there are strict rules as to what you can do with bats and balls. There is a lot more investment by manufacturers in studying the performance in both golf and tennis because there is money to be made by revising the equipment.”

Although Rosenberg has studied the intricacies and physics of baseball, he cherishes the simplicity of the game.

“I think baseball is a game that should be played on grass during the daytime,” he said. “That’s how it should be.”