# Golf Swing Physics

## and Other Forms of Slashing and Hacking

Guest article by Rod White  --  December 2008

Rod White is a physicist in New Zealand. At the end of 2008, he put together a PowerPoint presentation on the physics of the golf swing, and shared it with me. I felt it would make a great article explaining why the swing works the way it does, and offered to hammer his presentation into a web page. He agreed, and has given me permission to use the article on my site.

To make the presentation accessible to every golfer, Rod has removed the math from the core of the presentation and used animations and graphs to illustrate what’s going on in the golf swing. You will need to know how to read a graph, but hopefully that’s all.
For those who want the additional insights provided by the math and physics, mathematical notes have been placed in boxes like this. Feel free to skip the notes if Greek symbols and calculus have adverse side effects.
DaveT

Presentation prepared by Rod White
Measurement Standards Laboratory of New Zealand
PO Box 31310
Lower Hutt
New Zealand

Email : rodwhitenz_at_gmail_dot_com
December 2008

## 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.

## Outline of the Article

### References:

1. Theodore Jorgensen, The Physics of Golf (Springer Verlag, New York, 2nd ed, 1994)
2. C. B. Daish, The Physics of Ball Games Parts I and II (English Universities Press, London, 1972)
3. Alistair Cochran and John Stobbs, Search for the Perfect Swing (Triumph Books, Chicago, 1968)