In this blog post, we’ll explore why Oh Seung-hwan’s fastball appears to rise to batters, focusing on the Magnus effect—a key concept in fluid dynamics.
In 2011, the Korean Professional Baseball League featured many players who made headlines. Among them, Oh Seung-hwan—the “Closer King” who posted a 0.63 ERA, set various save records including the most saves in Asia, and led the Samsung Lions to the championship—was the player who garnered the most attention.
Let’s take a look at Oh Seung-hwan’s pitching schedule and pattern. He is a closer who takes the mound in the ninth inning when his team is leading by three runs or fewer to close out the game. He throws about 15 pitches per game, more than 90% of which are fastballs. The exact name for the fastball he throws is the “four-seam fastball.” A four-seam fastball is a pitch in which the ball interacts with the air four times as the seams rotate once while the ball travels forward with backspin. While many pitchers throw this type of pitch, South Korean professional baseball batters unanimously say, “The break on his pitch is different. It feels like the ball is alive, moving and rising.” So, let’s examine the principle behind why Oh Seung-hwan’s fastball appears to “rise” from the perspective of fluid mechanics, a key field of mechanical engineering.
To understand this phenomenon scientifically, the first factor to focus on is the ball’s spin. At the time, the average spin rate of fastballs thrown by South Korean professional baseball pitchers was approximately 41 revolutions per second, while Oh Seung-hwan’s fastball was known to spin at an average of about 47 revolutions per second, reaching as high as approximately 57 revolutions per second.
As a baseball cuts through the air and moves forward, it simultaneously spins in the opposite direction of its forward motion. It is precisely this backspin that is the main reason the fastball appears to rise. When the ball spins backward, the airflow over the top of the ball accelerates, while the airflow beneath it slows down relatively. As a result, a pressure difference develops between the top and bottom of the ball, and the ball is subjected to a force pushing it from the lower, high-pressure side toward the upper, low-pressure side. Consequently, the ball’s descent due to gravity is relatively slower than it would be without spin, making it appear to the batter as if the ball is rising.
To make this easier to understand, imagine air molecules as people walking down a crowded street. One side of the street is packed with people, making it very congested and slowing down movement. On the other hand, the other side has fewer people, allowing for free and rapid movement. People naturally tend to move toward the less crowded side, and in the process, a person standing at the boundary between the two areas is pushed toward the side with relatively fewer people. Here, the density of people corresponds to pressure, and the person at the boundary corresponds to the baseball. This phenomenon, in which a pressure difference is generated by rotation and that pressure difference alters the object’s trajectory, is called the “Magnus Effect.”
This phenomenon can also be explained by Bernoulli’s principle. Bernoulli’s principle states that the kinetic energy and pressure of a fluid are interconvertible, and the total energy remains constant. In other words, as the fluid’s speed increases, the pressure decreases, and as the speed decreases, the pressure increases. According to this principle, a back-spinning baseball experiences lower pressure on top and higher pressure on the bottom, resulting in upward lift. However, in a typical professional baseball game, a pitcher’s fastball does not actually rise; it continues to fall due to gravity. Yet, because the spin reduces its rate of descent, it appears to the batter as if it is rising.
When analyzed scientifically in this way, the phenomenon where Oh Seung-hwan’s fastball appears to rise to batters has a solid physical basis. This is not simply an exaggeration of his pitching prowess by batters, but an actual phenomenon that can be explained by fluid dynamics.
In baseball, South Korea’s most popular sport, pitchers actively utilize these principles of fluid dynamics. Oh Seung-hwan, in particular, has consistently thrown a powerful four-seam fastball, leveraging his exceptional velocity and spin rate to maximize the Magnus effect. In the future, when watching baseball games, if you think about these principles of fluid dynamics rather than just focusing on the final score, you’ll be able to appreciate every pitch thrown by the pitchers with even greater interest.
