Physics & Golf: Investigating Shaft Flex & Ball Direction

[Links Golfer]

Hello everyone,

I have a few questions relating to golf which i would like to understand further through physics.

My first question is related to the shaft flex of the club.
If the swing is perfect how would it be possible a shaft with to much flex for the player would cause the ball to travel left of the inteded target, i believe it should travel to the right of the intended target as the face of the club will be open at impact.
Can physics clear up this widespread belief, thank you.

 

[Meir Achuz]

The flex is there to try to increase club speed at impact. The downward swing must match the flex. What is meant by a "perfect swing" in this context is that it gets max speed at impact. Then the ball would go straight (other things also beng perfect). If the downswing is too fast, the club face would be lagging and the ball go to the right, but then it wouldn't be a perfect swing for that flex.

 

[FredGarvin]

It would make sense (to me anyways) that if the shaft had way too much flex in it that the person's hands would be very far in front of the club head at the time of impact. Conceivably I would expect that the club face would not have enough time to open up. But I think for that scenario to work that the effective club head speed would be slower as well.

I think it is a stretch to be able to say that you could have a perfect swing and too much flex as your conditions. If you have too much flex, doesn't that immediately infer that your swing can not be perfect? Just a thought there.

 

[russ_watters]

Yeah, the only way to have a perfect swing on a club with too much flex is to not swing as hard. And I would think that the flex would open the face more as well - remember, the club flexes torsionally too.

 

[Links Golfer]

The perfect swing is missleading, sorry.

Let's say Tiger Woods was handed his usuall driver with a lady flex shaft fitted, he attempts to hit a huge straight ball down the middle of the fairway not knowing the shaft has changed, his swing is his usuall Perfect swing for the shot he is trying to play, except he is armed with a shaft to whippy, which way will the ball travel from his intended target.

 

[Meir Achuz]

If the downswing is too fast, the club face would be lagging and the ball go to the right, but then it wouldn't be a perfect swing for that flex

 

[Links Golfer]

Thank you Meir Achuz, this question comes up because of a furious debate where i disagreed with the majority of those debating an issue.

The question related to shafts, if the shaft is too stiff which way would the ball travel, if too flexible which way would the ball travel.
Most people had put their google cowboy hat on and came back with "stiff will go right/flexy will go left". They state as a reason for the ball traveling right from a stiff driver is that "they cannot square the clubface" for some reason when they try a stiff they leave the face open and it travels right. SO what are they told to do, yes buy a shaft with more flex. Is that crazy or am i crazy?

 

[Meir Achuz]

If you are not the Tiger, but a 100 golfer, it could be that your downswing is so erratic that the flexed shaft has gotten ahead of your wrists, driving the ball to the left. So flex could go either way.
As a better (I hope) physicist than a golfer, I find experimentally that when I roll my wrists has the most effect on direction. Anyway, as Mickelson-Woods shows, golf is only half swing and the other 90% mental (to quote another bad golfer). Let's see what happens today at Ford.

 

[FredGarvin]

After thinking about this a bit more, I can rationalize the club face opening up on a shaft that is too flexible. This is a thought experiment, so I have to preclude this with the fact that I have no physical measurements to back this up...

It would have to be based on the distance between the clubhead's center of gravity and the axis of the shaft. The offset of the two is going to cause the clubhead to open up no matter what. So, with a LONGITUDINALLY flexible shat, that will increase the club head speed (to a point) and that will cause a greater torsional twist by the head, thus opening it up and causing the ball to go to the right.

The only scenario that I can not get to fit into this line of thinking is if the contact between the club head and ball are not instantaneous. If the length of contact is longer than expected, the possibility exists that the ball is "cradled" by the club head as the club head rotates back to it's equilibrium position to relieve the torsional deflection. That could guide the ball to the left.

I guess in the absence of any real studies or physical tests, I would have to go with anyone that has actually tried the two types of shafts. Of course, you'd want someone with a pretty repeatable swing (if that's possible in golf).

 

[russ_watters]

I have a bunch of old clubs that I could never hit and one of the things I credit with helping correct a persistent slice (from before I started playing a lot at age 22, until age 27) is a stiffer shaft. I bought a lot of cheap clubs hoping to get lucky and one thing most had in common was graphite shafts that were too flexible. However, I can't really be sure, because along with buying a decent driver, I also started lifting weights pretty seriously and one driver that I couldn't ever hit before I can kinda hit now. I swing hard - harder than I should - and if you aren't strong enough to get the club head around, you can leave it open.

 

[GENIERE]

… The offset of the two is going to cause the clubhead to open up no matter what. So, with a LONGITUDINALLY flexible shat, that will increase the club head speed (to a point) and that will cause a greater torsional twist by the head, thus opening it up and causing the ball to go to the right…QUOTE]

The ball will indeed start off to the right, but will immediately hook to the left. The induced horizontal rotation by the open clubface (gear effect) generates a non-vertical pressure differential and resultant hook.

 

[Homer Simpson]

My first hand experience tells me that too whippy and tourque'y of shaft can and did produce snap hooks a lot of the time. Thats not a nice draw, but a ball that turns right over about a 100 yards out and dives to the right (Im a lefty). I think it likely depends on the individuals swing. Usually the club shaft gets 'loaded' right when the downswing begins, some people load it a lot faster and more violently than others. I whip and clear my hands through fairly quickly at the bottom of the swing, and with the whippy shafts I'ld always be trying to prevent 'hooding' the driver. I think the shaft was unloading early and closing up the face. Long story short, I went up two notches in shaft flex and reduced the snap hook frequency a ton.

 

[Links Golfer]

After thinking about this a bit more, I can rationalize the club face opening up on a shaft that is too flexible. This is a thought experiment, so I have to preclude this with the fact that I have no physical measurements to back this up...

It would have to be based on the distance between the clubhead's center of gravity and the axis of the shaft. The offset of the two is going to cause the clubhead to open up no matter what. So, with a LONGITUDINALLY flexible shat, that will increase the club head speed (to a point) and that will cause a greater torsional twist by the head, thus opening it up and causing the ball to go to the right.

The only scenario that I can not get to fit into this line of thinking is if the contact between the club head and ball are not instantaneous. If the length of contact is longer than expected, the possibility exists that the ball is "cradled" by the club head as the club head rotates back to it's equilibrium position to relieve the torsional deflection. That could guide the ball to the left.

I guess in the absence of any real studies or physical tests, I would have to go with anyone that has actually tried the two types of shafts. Of course, you'd want someone with a pretty repeatable swing (if that's possible in golf).

That is something i have never heard of before Fred, and i can see where you are coming from with the "cradled by the clubhead", thank you. I will keep that onboard as i feel it is a very valid point, it could happen more often than people think. It strays a little from my question however as the player in my question is clearly overpowering the shaft all the way though the swing, the kick from the shaft will arrive after impact. Thanks again.

 

[Links Golfer]

… The offset of the two is going to cause the clubhead to open up no matter what. So, with a LONGITUDINALLY flexible shat, that will increase the club head speed (to a point) and that will cause a greater torsional twist by the head, thus opening it up and causing the ball to go to the right…QUOTE]

The ball will indeed start off to the right, but will immediately hook to the left. The induced horizontal rotation by the open clubface (gear effect) generates a non-vertical pressure differential and resultant hook.

It was my understanding gear effect (bulge on the face of the club) was more related to off centre hits with a squared clubface, well that's what the club manufacturers tell us.

Would the thin titanium face of the driver work like a spring if the bulge was not there?


Russ/Homer thank you.

 

[GENIERE]

It was my understanding gear effect (bulge on the face of the club) was more related to off centre hits with a squared clubface, well that's what the club manufacturers tell us.

Yes but if we assume the very flexible shaft lacks torsional rigidity there would also be some rotation of the club head around the center of gravity producing the 'gear effect' even if struck on the sweet spot.

Would the thin titanium face of the driver work like a spring if the bulge was not there?

I can only guess that it would.