How does perimeter weighting affect the moment of inertia of a golf club head?

[Duster22]

"In the last 25 years, designers have developed clubs that have approximately the same weight as the older clubs but have it distributed around the perimeter of the club, so that the head is far more resistant to off-center twisting and therefore far more forgiving of golf swings that are off line by a few millimeters."
http://entertainment.howstuffworks.com/sports/golf/basics/golf-club2.htm

I am trying to explain why perimeter weighted golf clubs are more resistant to off centre twisting than homogenous density clubheads using a physical model.I am having trouble figuring out what the club head's axis of rotation should be. Since it is fixed at the heel by the shaft, one might expect that to be the axis of rotation but then a collision in the centre of the clubhead would cause twisting.

Can anyone explain how perimeter weighted golf clubs lead to a straighter shot when balls are misgarbage (when the ball is hit with parts of the clubhead other than the centre)?

 

[Vagn]

"In the last 25 years, designers have developed clubs that have approximately the same weight as the older clubs but have it distributed around the perimeter of the club, so that the head is far more resistant to off-center twisting and therefore far more forgiving of golf swings that are off line by a few millimeters."
http://entertainment.howstuffworks.com/sports/golf/basics/golf-club2.htm

I am trying to explain why perimeter weighted golf clubs are more resistant to off centre twisting than homogenous density clubheads using a physical model.I am having trouble figuring out what the club head's axis of rotation should be. Since it is fixed at the heel by the shaft, one might expect that to be the axis of rotation but then a collision in the centre of the clubhead would cause twisting.

Can anyone explain how perimeter weighted golf clubs lead to a straighter shot when balls are misgarbage (when the ball is hit with parts of the clubhead other than the centre)?

I'd agree that the axis of rotation would be about the shaft of the club, perhaps manufacturers do this to maximise the moment of inertia without increasing the mass beyond the typical value for a given club. If you put the extra mass just on the far side from the shaft, then the club would feel unbalanced in the player's hands, which would also mean that it would have to be distributed relatively evenly across the club.

 

[Cleonis]

Can anyone explain how perimeter weighted golf clubs lead to a straighter shot when balls are misgarbage (when the ball is hit with parts of the clubhead other than the centre)?

I agree with Vagn that what is manipulated is the moment of inertia of the clubhead.

If the clubhead hits the ball perfectly centered then you get a simple transfer of momentum from the clubhead to the ball, with the clubhead following through in the same direction as before.
With an off-center strike the center of mass of the clubhead is not aligned with the center of mass of the ball. The clubhead will then turn, around its own center of mass. (This turning is dampened of course because the golfer is gripping the club, but some turn is inevitable.)


For a maximized example of difference in moment of inertia take the case of a bar that is one meter long, with two weights (say, spheres with a 10 cm diameter) that can slide along the bar.

If you position the two weights as close to the center as possible, and you push the bar slightly off-center (let's say the push is 5 cm off-center) then the bar will tend to turn. If you position the two weigths at the ends of the bar then the same off-center push gives much less turning, because of the larger moment of inertia.

I think that is why a perimeter weighed clubhead is somewhat more forgiving when hitting the ball slightly off-center.