"The scratch golfer was superior in coordinating his alpha torque so to release the maximum stored strain energy in the shaft at impact. This timing is important since the unflexing of the shaft can contribute to the club head velocity."
"Shaft flexibility plays a part in generating club head velocity. The straightening of the shaft continues to accelerate the club head through impact even after the work by the wrist on the club is done. Approximately half of the shaft stored strain energy is released by impact and converted to higher club head velocities."
quoted from:
http://www.jssm.org/vol4/n4/17/v4n4-17text.php
As previously concluded by Brian and confirmed by Mandrin, I thought the shaft is merely a timing mechanism which affects the impact alignments (such as the clubface and clubhead) of the golfer.
tongzilla,
Below is my critique of this paper by Nesbit posted about a year ago.
Nesbit/Serrano use three translational joints and three revolute joints to drive their club model. These are rigid elements. The golfer’s hands however are not rigid and interface the grip with soft biomechanical tissues. That makes a huge difference.
Put a driver in a vice and notice how remarkable long it will remain vibrating. Now put the club in the hands of someone instructed to keep a reasonable tight grip and try to oscillate the club. No way. Very simple demonstration and convincing proof.
The interface with the hands constitutes a substantial over damping of the oscillatory features of the golf shaft. One can also discuss this in terms of mechanical interface impedance between hands and shaft as being very soft.
All the sales hype about loading the shaft and it whipping/kicking forward, the frequency matching of shafts, it is all based on the behavior of a shaft as if being clamped in a vice. There is just only small problem – in a golf swing it is not.
Nesbit/Serrano mention the clubhead to return to its undeflected position near impact. Golf club experts/photographic evidence however will show that the shaft bends forward at impact. Not due to a forward kicking of the shaft but due to an inertial torque caused by the centrifugal force acting through the offset center of mass of the clubhead.
In short, an overdamped mechanical oscillatory sytem can’t be loaded with strain energy to be released as kinetic energy. However, let’s consider, just for arguments sake, that the approach and conclusion about the golf club by Nesbit/Serrano are correct. However they do mention:
“ The amount of strain energy absorbed and then released during the down swing is a very small percentage of the work transferred to the club.”
Hence, for all practical purposes, their very sophisticated shaft bending modeling can be considered to be a bit of an academic exercise, likely done for completeness and since their very sophisticated commercial modeling software package readily allowed it.
References:
Nesbit S, ‘A Three Dimensional Kinematic and Kinetic Study of the Golf Swing’.
JSSM-2005,Vol. 4, Issue 4, 499-519
Nesbit S and Serrano M, ‘Work and Power Analysis of the Golf Swing’.
JSSM-2005,Vol. 4, Issue 4, 520-533
