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About this Article
Written by: Brian Amanatullah, Adam Nazar
Written on: September 2nd, 2002
Tags: sports & recreation, aerospace engineering
Thumbnail by: Tage Olsin/Wikimedia Commons
About the Author
In the Fall of 2002, Brian Amanatullah was a student at the University of Southern California, in his second year in Computer Engineering and Computer Science. He enjoys playing baseball and other sports. In the Fall of 2002, Adam Nazar was a Computer Science and Computer Engineering major at the University of Southern California. His years of baseball experience and interest in engineering prompted him to undertake this project to further understand the physics behind the sport.
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Volume IV Issue II > Curveballs and Knuckleballs: Engineering Principles at Work in America's Favorite Pastime
The art of pitching a baseball requires great skill and dexterity to master. A great pitcher is one who understands the engineering of the baseball itself and the aerodynamic principles at work while the ball is in flight. Furthermore, a great pitcher is able to exploit these laws of physics with a variety of pitches, each having a different velocity and trajectory. The pitcher uses different types of pitches to confuse the batter, thus gaining the upper hand. Two types of pitches that are very effective in allowing the pitcher to gain the advantage are the curveball and knuckleball. The curveball's curving trajectory results from the direction of the ball's spin, and the orientation of the stitches. On the other hand, the knuckleball relies on a very slow rotation and turbulent airflow. By understanding the structural engineering behind a baseball, the aerodynamics of the baseball, and the manner in which the ball is gripped and released, one can gain a greater appreciation for the science of pitching.

Introduction

Pitching a baseball is a finely honed skill, requiring great athleticism and years of practice to master. To pitch is not to merely throw the baseball across the plate, and even those who can throw with great speed and accuracy may not find success as pitchers. A great pitcher has an arsenal of pitches, each thrown with a different velocity and trajectory. With balls pitched at nearly 100 miles per hour, a batter has less than a second to determine what type of pitch it is, anticipate the location of the ball as it crosses the plate, and swing a 40 ounce bat over 100 miles per hour. An unpredictable pitch, then, can confuse a batter and give the pitcher a great advantage. Two such unpredictable pitches are curveballs and knuckleballs. These two types of pitches depend on the pitcher's grip on the ball, the aerodynamics of the ball as it travels toward home plate, and the engineering behind the ball itself.

The Anatomy of a Baseball

A baseball consists of three main parts: the core, the shell, and the stitches. The outer portion of the baseball is what helps to create the curve in a curveball or the wildly erratic movement of a knuckleball . The core, which is a solid piece of cork with a nine inch circumference weighing roughly five ounces, is not relevant to the engineering of such pitches. The shell and stitches have the most effect on a ball's flight through the air.The shell of the baseball is made up of two peanut-shaped pieces of cowhide, which are 8 inches in length and range in width from 2 inches at the larger end to 1 inch along the shorter parts (Fig. 1). They are extremely smooth and air travels over them easily. A baseball would be a nearly smooth sphere if not for the stitches used to connect these two pieces together.
Roger Smith/U.S. Library of Congress
Figure 1: The halves of two baseballs, illustrating the composition. On the left, a traditional cork-centered ball, and on the right, a rubber-centered ball used during World War II because of wartime material shortages.
The stitches of the baseball are used to sew the two pieces of the shell together around the inner core. The stitches form a pattern on the ball. The stitches wrap around the two peanut-shaped pieces to create a three dimensional outline of a hyperbolic paraboloid, which resembles a saddle. The stitches play an extremely important role in the flight of the ball through the air since they are responsible for altering the air flow around the ball [1].