Dynamic characterization of golf equipment

In the golf swing the shaft, head, and ball respond at different time scales. The shaft is swung from the top of the back swing to impact in less than a half second. In that time, the shaft loads and unloads in different ways for different shafts. Natural frequencies and mode shapes characterize different shafts uniquely making some shafts better than others for individual golfers. Shafts are benchmarked by measuring their stiffness profile along the length of the shaft. Knowing this, a shaft finite element model is generated from which the natural frequency is found. Shaft zone frequencies, an important fitting method, are cantilevered natural frequencies found from the stiffness profile. As for golf balls, their core and cover mechanical properties influence performance and feel. The loading of the golf ball occurs in 0.0005 s. Golf ball stiffness and damping properties are measured using DMA and universal testing machines. Distance balls have cores that are nominally twice as stiff as performance balls, making them feel harder to the golfer. Performance and distance balls also respond to strain rate changes differently. Ultimately, stiffness properties affect the initial velocity, spin, and launch angle which dictate the distance the ball flies.