As I watched my beloved Yankees defeat the Phillies to win the 2009 World Series two weeks ago, several questions popped into my head regarding the science of the game.
I'm a pretty casual fan, so maybe it was because I had spent most of the week in the library studying that I had my "the way things work" cap on. But something about watching A.J. Burnett throw filthy sliders past helpless Philadelphia batters made me curious about the science behind America's pastime.
Understanding how a baseball is pitched involves both standard equations and more advanced topics in physics, ranging from velocity, distance and height vectors, to forces such as drag, air resistance, Magnus effect, rotational velocity and pressure zones.
An important thing to realize about baseball pitches is that from the time the pitcher releases the ball, it is a matter of mere milliseconds before the ball reaches the plate, leaving the batter with a microscopic reaction time.
Also, gravity is at work in the sense that the ball will drop over the duration of the pitch. The distance from the mound to home plate is 60 feet and six inches and the average major league fastball is around 90 miles per hour, so it takes a lightning fast .458 seconds for the ball to reach home plate from the pitcher's mound.
Using time to solve for the height vector and assuming a pitcher's height to be six feet, gravity causes a drop of approximately 3.4 feet. Fastballs have a backspin that gives them a fairly stable aerodynamic flight and a predictable trajectory. The curveball, however, is a different story.
A curveball is one of the most useful pitches in the game of baseball. Burnett, for example, uses the pitch with great regularity and is often thought to have the best one in baseball. The curveball is thrown by the pitcher such that the palm and fingers are over the top of the ball upon its release, giving it a downwards or sideways spin.
The point at which the ball breaks, or changes direction, is determined by when the pitcher snaps his wrist. Snapping the wrist earlier in the motion causes the ball to break earlier, and snapping it later will cause the ball to hold its path longer and curve later.
Baseballs are designed with 216 raised stitches, which curveball pitchers grip with their middle and index fingers. According to researchers at the University of Alaska-Fairbanks, as the pitcher spins the ball, the stitching gathers up air while it is rotating, creating a higher air pressure on one side of the ball.
This stress makes the air flowing around the ball break away from the surface sooner. The air at the top of the spinning ball is subject to less stress and hangs onto the ball's surface longer. Because of this phenomenon, the curveball does most of its curving in the last quarter of flight.
This imbalance of force is called the Magnus effect - the idea that the pressure on one side of the ball is greater than on the other side. For a slider, the high pressure zone on top keeps the ball downward in flight. Combined with gravity this produces an exaggerated drop in flight, making the pitch hard for the batter to track.
Another interesting pitch to look at from a physics perspective is the knuckleball. The knuckleball is a pitch with an erratic and unpredictable motion. The most famous active knuckleballer is Tim Wakefield of the Boston Red Sox, who has made an eighteen year professional career out of mastering the pitch.
The knuckleball has very little, if any, spin. This creates a vortex over the seams of the baseball, causing the pitch to change directions in mid-flight. As Red Sox Gold Glove catcher Jason Varitek said, "Catching the knuckleball, it's like trying to catch a fly with a chopstick."
According to a 1975 article in the American Journal of Physics, scientists in the Mechanical Engineering department at Tulane studied the erratic motion of the knuckleball by measuring forces on the ball in a wind tunnel. Their results showed that, similar to a curveball, the nonsymmetrical location of the seams gives rise to a nonsymmetrical lift force.
A very slowly spinning knuckleball will have a lateral force exerted upon the ball that changes as the positions of the laces change. A two-dimensional analysis of the trajectory of the baseball indicates that the measured force can cause a deflection of the baseball's trajectory of more than a foot. An effective knuckleball should be thrown so that it barely rotates on its way to home plate.
This only explores half the physics of baseball, as there are many more forces at work when it comes to hitting. However, it is safe to say the science of baseball has become a serious subject in the academic world. Alan Nathan, a professor at the University of Illinois, for example, teaches an entire class devoted to the physics of baseball.
Advances in this field of study mean that the next time you watch A.J. Burnett or Tim Wakefield pitch, you can impress (or annoy) your friends with your new dimension baseball knowledge.
