In this blog post, we’ll examine how the dimples on a golf ball’s surface reduce air resistance and increase driving distance from a fluid dynamics perspective.
In golf, driving distance—the distance the ball travels—is one of the key factors that distinguish professional players from amateurs. Consequently, the ability to hit the ball far holds great significance in golf. For this reason, unlike balls used in other ball sports, a golf ball has a unique surface covered with countless small dimples. So, how do these small dimples make the ball fly farther? And to what extent does this structure actually affect driving distance?
Before explaining this, it is necessary to first understand two concepts. The first is the concept of turbulence, which describes the flow of a fluid. Turbulent flow refers to the phenomenon where fluid particles move irregularly as they flow, and it is the opposite of laminar flow, which exhibits a regular flow pattern. This irregular flow makes collisions and energy exchange between fluid particles more active. The second concept is the separation point. The separation point refers to the point where a fluid, after flowing along the surface of an object, breaks away from that surface. When the fluid flowing along the object runs out of kinetic energy, it breaks away from the surface; beyond this point, the fluid swirls, forming a flow that loses its consistent directionality. The pressure in this region becomes lower than that in front of the object, and this pressure difference affects the forces acting on the object. Understanding the concepts of turbulence and the separation point makes it easy to grasp the role of the dimples on a golf ball.
The air resistance acting on a flying golf ball is broadly divided into pressure drag and frictional drag. Pressure drag is resistance caused by the pressure difference formed between the front and back of the object, while frictional drag is caused by friction between the air and the object’s surface. In the case of a golf ball, pressure drag accounts for the majority of total air resistance; therefore, reducing this drag can significantly improve driving distance. So, how do the small indentations on the surface of a golf ball—known as dimples—reduce pressure drag?
When the ball’s surface is smooth, the airflow remains mostly laminar but separates from the ball’s surface at a relatively early stage. In contrast, on a golf ball with dimples, the air is repeatedly disturbed by the dimples, causing the laminar flow to transition into turbulent flow. Because turbulent flow continuously exchanges energy with the surrounding fluid, the air can flow along the ball’s surface for a longer period of time; as a result, the separation point forms further back than on a smooth ball.
As explained earlier, the pressure behind the separation point is lower than that in front of the ball. This pressure difference formed between the front and back of the ball creates a force opposite to the direction of air flow, generating aerodynamic drag. However, with a dimpled golf ball, as the separation point moves farther back, the size of the low-pressure region is relatively reduced. Consequently, the pressure difference between the front and back of the ball decreases, and the aerodynamic drag generated by the air also decreases.
So, how much of a difference does this effect actually make? Generally, the aerodynamic drag of a golf ball is compared using the drag coefficient. In the Reynolds number range typical of actual golf ball flight, the drag coefficient of a dimpled golf ball is known to be significantly lower than that of a smooth ball. At the time this manuscript was written, it was sometimes explained that the drag coefficient was reduced by about half and that the difference in carry distance could be as much as double; however, based on a synthesis of current research findings, it is difficult to generalize that carry distance simply doubles, as it is influenced by various factors such as swing speed, launch angle, spin rate, and ball structure. However, it remains true that dimples are a key factor in significantly improving flight performance by effectively reducing air resistance and increasing lift.
The Reynolds number is a representative dimensionless number used to determine whether fluid flow is laminar or turbulent. This value is determined by the fluid velocity, the characteristic length of the object, and the viscosity of the fluid. In practice, golf balls fly within the Reynolds number range where turbulence forms, taking into account their diameter, flight speed, and the viscosity of the air. Therefore, the dimples on a golf ball are designed to function most effectively under these conditions, serving to control airflow and increase flight distance.
The serendipitous discovery that a worn ball with surface scratches flies farther than a smooth one has led to the development of today’s golf ball dimples. As we have seen, the dimples on a golf ball are not merely decorative patterns. Dimples transform airflow from laminar to turbulent, shift the separation point aft, and reduce the pressure difference formed between the front and rear of the ball. As a result, aerodynamic drag is reduced, allowing the golf ball to fly farther and more stably.
Golf balls used today are aerodynamically engineered with precision, down to the number, size, depth, and arrangement of the dimples. While design methods vary by manufacturer, they all share the common goal of reducing air resistance and optimizing flight performance. Thus, each small indentation on the surface of a golf ball is the result of scientific design based on the principles of fluid dynamics and has become a key factor in enhancing the ball’s distance and flight stability. These indented dimples are by no means a random formation; rather, they are a scientific structure created to effectively control airflow.
