This blog post scientifically examines the principle behind how the unique dimples on a golf ball’s surface influence its flight distance.
Modern people are passionate about ball sports. We cheer for Messi or Ronaldo’s exquisite shots, marvel at Ryu Hyun-jin’s fastballs, and watch Tiger Woods’s incredible driver shots with bated breath. In this way, we pay close attention to the movement of the ball and love it. However, among the balls used in ball sports, there is one that is unusually distinctive. Most balls are smooth or have only subtle ridges, but golf balls are different. Golf balls have so many dimples it’s hard to count them on both hands. Some might compare them to the seams on a baseball, the rubber cord on a tennis ball, or the panels 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 significantly larger than on other balls.
In fact, the dimples on a golf ball are closely tied to the history of golf. Golf began to gain popularity among European nobility in earnest from the 16th century. Early golf balls were smooth, spherical balls made of wood. However, when durability issues arose with wooden balls, players began using round balls made of leather. Here, a curious phenomenon was discovered. They discovered that a ball that was old and worn, with a bumpy surface and slightly dented, flew much farther than a new, perfectly smooth ball. This finding puzzled European nobility, as in most ball sports, a new ball typically enhances performance over an old one.
The solution came from researchers at golf ball manufacturers, who were mechanical engineers. One crucial field within mechanical engineering is fluid mechanics, which studies the properties of fluids. This enabled mechanical engineers to analyze the movement of golf balls. This phenomenon can be simply explained by understanding ‘drag acting on objects moving through a fluid’. Drag refers to the resistance that impedes the motion of a moving object, with friction being a prime example.
The drag force acting within a fluid can be broadly divided into form drag and frictional drag. Form drag is the resistance force generated by the pressure difference acting on a moving object. For example, when we run a 100-meter dash, the resistance force caused by the increased air pressure in front of our body and the decreased pressure behind is called form drag. In contrast, frictional drag is the resistance force caused by the viscosity of the fluid. Honey flows slowly down a slanted surface due to its high viscosity, which acts as a resistance force hindering movement. Gases like air have low viscosity, so the frictional resistance on objects moving through air is very small and can be practically ignored. Therefore, we only need to focus on the golf ball’s shape resistance.
As the ball flies, air flows along its surface until it begins to separate from the surface at a certain point. When a smooth ball moves through the air, the flow of air over its surface is straight. This is called laminar flow. However, if the air separates from the ball’s surface starting from the middle, the air speed behind the ball drops sharply, causing a separation phenomenon. Separation is the phenomenon where the air splits into two layers. As the airflow weakens, the air pressure decreases. A large pressure difference develops between the front and rear of the ball, increasing the shape drag. Consequently, a smooth ball travels a relatively short distance.
Conversely, a ball with dimples or an uneven surface generates turbulent flow. Air moves along the dimples on the golf ball’s surface, no longer flowing in a straight line. In turbulent flow, the airflow is curved, and separation occurs at the rear of the ball. This reduces the pressure difference and decreases aerodynamic drag, allowing the golf ball to travel farther.
Ultimately, grooves on the golf ball’s surface reduce the aerodynamic drag acting on the ball, allowing it to travel farther. In this way, engineering knowledge is deeply embedded in our daily lives and will continue to exert an ever-greater influence. This is because engineering knowledge is not merely theory; it is an excellent tool for understanding and analyzing the world we live in.
