Golf Swing Physics

Introduction

I am a physicist and a keen golfer. A few years ago I was under doctor’s orders to stay away from golf for at least 3 months in order to recover from a shoulder injury. So instead of playing, I trawled through golf books and papers to figure out what actually happens in the golf swing. After many months, I had a good pile of paper describing a lot of things about golf, but nothing simple to tell me how the swing really works.  Even the best of the classic books like Cochrane and Stobbs, Daish, and Jorgensen fail on this point.  Once I was back playing, the problem continued to nag.

The underlying problem with golf-swing physics is the complexity of the math. The equations explain everything and nothing. Sure it is possible to solve the equations, produce animations, and carry out numerical experiments, which is what most researchers have done, including me. However, the equations are so complex that it is not possible to look at them and say, “Ah ha! – I understand.”

Eventually I found the simplification that provides the insight, and this presentation is the result.

The presentation builds the whole of the golf stroke including the swing and the club-ball collision. The key points of technique identified here are simple but so counterintuitive that they are hard to believe and execute when you are standing over a ball. The physics explanation helped me to defeat my intuition. I’m in my 50’s now and 30 years of bad wiring in the brain is hard to change, but over a period of two years I have gained 30-50 m distance on my drives, and improved the accuracy on all of my shots, all with less effort. Hopefully these pages will help you to do the same.

A careful reading of the presentation will take about an hour, and for most people it’s probably necessary to view the animations to really understand how the swing works. If you don’t have an hour, you can try reading the technique section by itself, but you may find some of the advice hard to believe.

The golf swing is a combination of two physical processes: most obviously, a collision between the club and ball, and perhaps less obviously, the unfolding of a simple machine called a double-pendulum.  Although simple, the double pendulum has very complicated behavior. In recent years, it has received a lot of attention because is a simple example of a system exhibiting chaotic behavior (which may explain some of my golf shots).   The double pendulum also turns up in a lot of different places because it is an efficient way of transferring energy from a heavy slow-moving object to a light fast-moving object:

• Baseball, tennis, hockey, and wood chopping are obvious examples.
• Football (kicking), javelin, and discus are not so obvious examples.
• Old war machines: Trebuchet (like a catapult), sling, atlatl or spear thrower (also known as the woomera in Australia).
• Builders and shipping cranes (especially on ships where it causes trouble), and the threshing flail.