In this blog post, we’ll take a scientific look at how the unique dimples on a golf ball’s surface affect its distance.
People today are passionate about ball sports. We cheer for the exquisite shots of Messi and Ronaldo, marvel at Ryu Hyun-jin’s fastballs, and watch Tiger Woods’s massive drives with bated breath. In this way, we focus on the movement of the ball and love it. However, among the balls used in ball sports, there is one that looks particularly unusual. Most balls are smooth or have only slight ridges, but golf balls are different. A golf ball has so many dimples that it’s hard to count them all on one hand. Some might compare them to the stitching on a baseball, the rubber lines on a tennis ball, or the seams on a soccer ball, but considering the relative size of the ball, the proportion of the surface covered by dimples on a golf ball is far greater than on other balls.
In fact, the dimples on a golf ball are closely tied to the history of the sport. Golf began to gain popularity among European nobility in the 16th century. Early golf balls were simply smooth, spherical balls made of wood. However, when durability issues arose with the wooden balls, people began using round balls made of leather. It was then that a curious phenomenon was discovered. It turned out that a ball that had been used for a long time—one with a bumpy surface and slight dents—traveled much farther than a brand-new, perfectly smooth ball. This discovery sparked great curiosity among the European nobility. This is because, in most ball sports, a new ball helps improve performance compared to an old one.
The people who solved this problem were researchers at golf ball manufacturers, composed of mechanical engineers. One of the key fields in mechanical engineering is fluid mechanics, which investigates the properties of fluids. Through this, mechanical engineers were able to analyze the movement of golf balls. This phenomenon can be easily explained by understanding the “drag acting on an object moving through a fluid.” Drag refers to the resistance that hinders the motion of a moving object, with friction being a prime example.
The drag acting within a fluid can be broadly divided into shape drag and frictional drag. Shape drag is the resistance caused by pressure differences acting on a moving object. For example, when we run a 100-meter dash, the resistance caused by the higher air pressure in front of our body and the lower pressure behind it is called shape drag. On the other hand, frictional drag is the resistance caused by the viscosity of the fluid. Honey flows slowly down a honeycomb surface due to its high viscosity, which acts as a resistance that impedes movement. Gases like air have low viscosity, so the frictional resistance of an object moving through air is very small and can be practically ignored. Therefore, we only need to focus on the shape resistance of the golf ball.
As the ball flies, air flows along its surface until, at a certain point, it begins to separate from the surface. When a smooth ball moves through the air, the flow of air along its surface is straight. This is called laminar flow. However, if the air begins to separate from the ball’s surface starting from the middle, the airspeed behind the ball drops sharply, causing a phenomenon known as separation. Separation is a phenomenon where the airflow splits into two layers; as the airflow weakens, air pressure decreases. A significant pressure difference develops between the front and rear of the ball, increasing aerodynamic drag, which is why a smooth ball travels a relatively short distance.
In contrast, a ball with grooves or an uneven surface generates turbulent flow. As air moves along the grooves on the golf ball’s surface, it no longer flows in a straight line. In turbulent flow, the airflow becomes curved, and separation occurs behind the ball. This reduces the pressure difference and decreases aerodynamic drag, allowing the golf ball to travel farther.
Ultimately, carving grooves into the surface of a golf ball reduces the aerodynamic drag acting on it, allowing the ball to travel farther. In this way, engineering knowledge is deeply embedded in our daily lives and will continue to have an ever-greater impact. This is because engineering knowledge is not merely a theory but an excellent tool for understanding and analyzing the world we live in.
