WHY DO GOLF BALLS HAVE DIMPLES?

The aero of a golf ball is a fascinating topic that has been explored for decades. The principles of aerodynamics and fluid dynamics define the flight behaviour of a golf ball, which is majorly influenced by its dimples; a common feature in this article. In fact, the golf ball was originally a ‘perfect’ sphere. It was only after observing the flight of scuffed and worn balls, that these balls would accelerate faster and attain more lift.

To touch on the first point of dimples increasing the acceleration, this is a result of less drag acting against the ball. Drag is the force that opposes the motion of an object through a fluid, in this case air. When a golf ball is in motion, the air molecules in front of the ball are compressed and pushed out of the way, creating a turbulent wake (a region of turbulent air behind a solid object as it moves through the fluid or gas). This wake generates a great deal of drag, which slows the ball down

Figure 1 above demonstrates how a smooth ball would fare The front is exposed to oncoming air which flows unopposed (and quickly) on the back, resulting in a broad wake behind the ball. A larger wake increases air pressure behind the object, decreasing the pressure gradient and so increasing drag

The dimpled ball of Figure 2, shows how the airflow differs after first contact Dimples disrupt the turbulent wake created by the ball; small pockets of low-pressure air that cling to the ball are created, which in turn increases the time of contact between the ball and the air These pockets are known as the "boundary layer" of air, and it reduces the drag on the ball, as the turbulent wake is thinner. This is why a dimpled golf ball will travel further

Another perk of the dimpled golf ball, briefly mentioned before is increased lift. Provided there is sufficient backspin, the air molecules on the top of the ball are moving faster than at the bottom and so there is a difference in pressure above and below the ball. On a dimpled ball, similar to the previous explanation, the lower pressure on the top of the ball creates a lifting force, while the higher pressure on the bottom creates a drag force.

Once again, the dimples on the surface of the ball disrupt the turbulent wake to form a boundary layer, hence reducing drag on the ball and helping to create lift. The amount of lift generated by the dimples on a golf ball is also affected by the shape and size of the dimples Smaller and deeper dimples create more lift, while larger and shallower dimples create more drag. This is because deeper dimples create a greater difference in pressure (due to a thinner wake), and smaller dimples create a more stable boundary layer of air.