# Physics of the Golf swing

I hope this comes under the classic physics roof. Do any of you play the game and would like to offer your opinions on the physics of the club swinging into and propelling the ball toward the target?

If any would like to take on a problem of shaft flex I would enjoy hearing about your views. Here goes: As a good player swings the club the golf shaft flexes. All shafts ( steel or graphite) have different flexes ranging from extra-stiff ( think telephone pole) to ladies flex. ( think fly rod ). Now the problem is this: Will increasing flex ( bending) on the downswing increase the players distance. I know for a fact ( empirical here) that a too flexible shaft decrease accuracy, however I would like to hear thoughts on distance only versus flexibility. Some parameters if you like, Head mass is 200 grams and shaft length is 44 inches. Lets not get into materials. Shaft weight is a compromise between steel and graphite and for argument sake lets say shaft mass is 85 grams.

Regards, FDB

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LURCH
Just off the top of my head, I would have to say that shaft flexibility must effect distance. At the moment of contact, energy is transferred from the clubhead to the ball. At that instant, two things happen; the ball accelerates foreword and the clubhead accelerates backward (decelerates). There is only a certain amount of energy generated by the impact between these two. Whatever portion of that energy is expended in accelerating the clubhead backward is energy not available to accelerate the ball forward.

This energy transfer could be pictured in the form of an "explosion" of energy between the ball and the clubhead. If you imagine placing a golf ball and the head of the golf club next to each other with a small explosive charge (perhaps a firecracker) between them, you can see that when the explosive detonates the energy from that detonation will push on both objects. If the clubhead is not attached to anything, both objects are equally free to move. Both will travel equal distances (d) in opposite directions from the point of the explosion (if we use a clubhead that's the same mass as a golfball). If the clubhead is attached to a very flexible shaft and the other end of that shaft is held stationary, then the clubhead might only travel 1/2 as far, (.5d) in which case the ball should travel twice as far (2d). Given a more rigid shaft, the clubhead could be restricted to traveling only 1/10 that distance (.1d), directing the remainder of the available energy to propel the ball nine times as far (9d).

These differences are, of course, greatly exaggerated. However, the principal which they illustrate remains sound.

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Thanks, anyone else have thoughts?

russ_watters
Mentor
Shaft flex is directly related to swing speed. The idea is that the shaft should be perfectly straight when you strike the ball (otherwise you get the inaccuracy you were talking about, plus you don't recover all of the energy from the flex). When you are accelerating the clubhead, it lags behind, bending the shaft. When you get to the contact point, it bends back, adding energy to the shot. The faster your swing, the stiffer the shaft has to be to "rebound" in time to be straight at the contact point. A stiffer shaft has a higher natural frequency than a more flexible one, and you essentially tune the frequency to your swing speed.