Tribology and golf
By R. David Whitby, Contributing Editor | TLT Worldwide July 2024
Friction between the golfer’s hand and the club is important for successful control of the club.
At this year’s STLE Annual Meeting, there was a small minigolf challenge near the membership booth. Although I have written several columns about tribology and sports, I have not yet tackled the subject of golf.
Most people who play golf do so for the pleasure of good company and fresh air. It would seem that only the professional players know that the laws of physics govern the game of golf. It is the interactions between the golfer, the clubs and the ball that determine when and how the ball goes into the hole on each green.
When the club hits the ball on the tee, the force applied by the club is the main factor in determining the distance the ball will travel. Other factors include the angle of the clubhead at which the force is applied, gravity, wind direction and air resistance. A golfer hitting a powerful drive requires more than just coordination and strength.
A smooth golf swing is one key to a golfer’s ability to control the direction and velocity of the ball, whether when driving, pitching, chipping or putting. An effective golf swing is the same as a double pendulum motion. The top pendulum is the triangle formed by the arms and shoulders of the golfer rotating from the fulcrum of the sternum in the middle of the chest. The bottom pendulum is the hands and golf club swinging from the hinge (fulcrum) of the golfer’s wrists.
An effective swing also relies on the golfer’s grip on the club, and their stance and alignment with respect to the ball. With any of the three types of grips, friction between the golfer’s hand (and glove) and the club is important for successful control of the club.
Having the right stance and posture lays the groundwork for a solid golf swing. A golfer needs to align their body parallel to the target line to ensure a square clubface at impact, leading to accurate shots. A relaxed, athletic and maintained posture throughout the swing enables a smooth and fluid motion, unlocking the full potential of the clubhead speed and control.
The force of the clubhead on the ball results in the ball being compressed and applying an equal and opposite force on the club. The impact of this equal and opposite force has little effect on the continuation of the swing. This initial force of the club causes the ball to project off the clubhead.
The golf club only comes into contact with the ball for less than a millisecond. The face of the club is grooved so that, during contact with the ball, friction imparts backspin to the ball. To make the ball travel further, a golfer needs to increase the acceleration of the ball by increasing the force with which the ball is struck or by swinging the club faster.
When the ball is in the air, the forces of gravity, aerodynamic drag and aerodynamic lift affect its flight. Each of these acts independently. Golf balls are dimpled and so fly farther, due to the combination of drag and lift. Dimples cause the boundary layer on the ball’s upstream side to transition from laminar to turbulent. The turbulent boundary layer remains attached to the surface of the ball much longer than a laminar boundary, with fewer eddies. This creates a narrower low-pressure wake and hence less pressure drag, allowing the ball to travel further. Backspin generates lift by deforming the airflow around the ball, similar to an airplane’s wing. This is called the Magnus effect. The turbulent airflow results in more Magnus lift than a smooth ball would experience.
When the ball hits the ground, the kinetic energy generated by the club, that has not been lost to drag (friction), has to go somewhere. A lot of it goes back into the ball, giving it more force to pop back into the air. The higher the potential energy, the higher the kinetic energy, and the higher the kinetic energy, the higher the bounce. When the ball eventually stops, it must either be hit again, further up the fairway, or gently rolled toward and into the hole. During its rolling along the green, friction with the grass will determine how quickly or slowly it will roll and how hard it needs to be hit with the putter.
Consequently, it could be useful for golfers to know something about tribology.
David Whitby is chief executive of Pathmaster Marketing Ltd. in Surrey, England. You can reach him at pathmaster.marketing@yahoo.co.uk.