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Post by natep on Dec 15, 2011 13:43:47 GMT -5
I've read the Miura paper and one of the models he uses has an actuator (?) that pulls/moves the center of rotation while the mass is whirling around. IIRC Mandrin had a model in one of his papers that shortening the radius without moving the center of rotation had the exact same result. Would shortening the radius be equivalent to pulling along the centripetal force vector, as he stated above? Is he wrong about shortening radius? Thanks.
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Post by gmbtempe on Dec 15, 2011 14:53:23 GMT -5
What makes so-called parametric acceleration happen is the velocity vector of the club head (cg of the club actually but just assume all mass is in the ch) not being normal to the direction of the force from the shaft. Were it possible to decrease the length of the shaft during the swing (by supplying excess centripetal force) this would accomplish the same thing as moving the center of rotation. You're making the velocity vector of the club mass not line up with the path it must follow as dictated by the kinematics and that slight difference creates a force in the tangential direction which can accelerate the ch. To wrap your mind around Parametric acceleration do this. Fetch a hex nut, a length of string a nail and a hammer from the garage. Pound the nail in just a bit on the edge of a wooden table so you can drape the string tied to the hex nut over it. Swing it like a simple pendulum... Now add some PA. as the nut reaches the nadir of its arc, slightly tug on the string. Play that excess out as it nears the top and begins to reverse direction. Repeat. After a few cycles you should notice the amplitude of the pendulum oscillation is increasing. That is parametric acceleration! BTW it works the other way as well. Let some string out near the nadir and pull in near the top and the pendulum amplitude will decrease. THis is where this comes from... vibration damping research. The difference is in golf we're applying parametric acceleration for the duration of the 2 final stages of the downswing not just the last instant. This in effect is what the constricting hand path is achieving for us. How is the PA applied in the golf swing? When I was working with Denny Alberts a couple years back we aided the inward pull during the downswing with a small "counterfall" transfer that fell like you were slightly fall away from the target line with your body. It was at this time that I suddenly started hitting the ball much further but I also attributed that to having less throw away.
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Post by gmbtempe on Dec 15, 2011 15:46:19 GMT -5
Watching Austin he is yet another player who swings "over" he backswing path (if that makes sense).
For so many years I had been told to drop it into the slot. He gets his hands very deep to start the swing.
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Post by imperfectgolfer on Dec 16, 2011 12:16:17 GMT -5
Nmgolfer, Very nice! I never could understand how the BM-groupies could believe that a CP-force would be responsible for the speed of the clubhead through impact. Now, how do you explain the fact that the clubhead does not pass Jamie's hands (from a rotational perspective) in the first 12-18" after impact - considering that his clubhead speed at impact is 140+ mph? Jeff.
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Post by imperfectgolfer on Dec 16, 2011 12:58:44 GMT -5
What do you think of my explanation for why the clubhead doesn't pass the hands soon after impact? I believe it is due to the difference in release biomechanics/mechanics. BM's RACP release action involves a release action where he essentially throws the clubhead at the ball in order to maximise clubhead speed through impact. In my personal approach using an intact LAFW I stroke the ball by swinging an intact LAFW through impact - like Federer performing a backhanded tennis stroke. Roger's racquet never bypasses his FLW after impact (from a rotational perspective) because he is moving his FLW non-stop through impact and beyond impact at a speed that prevents the racquet face from bypassing the FLW. Jeff.
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Post by imperfectgolfer on Dec 16, 2011 14:15:59 GMT -5
nmgolfer - you wrote-: "Could be... On the other hand I suspect a golfer's wrists are no match for the torque of a releasing club even if their intent is to maintain a FLW. Mind you I refer to the full swing with driver or other not some wimpy little pitch shot." So, how do you explain why all these golfers have successfully maintained a FLW, and avoided flip-bending their left wrist, until at least the P7.2 position (and often to the P7.5 position or beyond the P7.5 position) - when hitting a driver. Robert Rock Tiger Woods Jamie Sadlowski Dustin Johnson Slicefixer's student - Matt Note that Tiger Woods, Dustin Johnson and Matt have maintained a FLW beyond the P7.5 position. Jeff.
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Post by imperfectgolfer on Dec 16, 2011 14:32:07 GMT -5
nmg,
I do not see any explanation in post #11.
Jeff.
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Post by natep on Dec 16, 2011 15:14:29 GMT -5
Thanks for the update, nmgolfer!
Jeff, I would submit that all those golfers are throwing the clubhead into the ball, but the collision slows the clubhead down considerably. I believe if they swung just as hard in a practice swing the left wrist would likely bend immediately after low point.
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Post by imperfectgolfer on Dec 16, 2011 15:26:43 GMT -5
Natep,
Do you have any "evidence" to support your opinion? It is my strong opinion that it would have little/no effect - and that it is just as easy to maintain a FLW to P7.5 using an intact LAFW/FLW swing action even if the ball is not present, or if one uses of those plastic balls. When viewing skilled golfer's practice swings, I have never seen a greater degree of flipping between P7 and P7.5 if they are concentrating on performing an intact LAFW-stroke action (like their regular swing) and if they are not simply throwing the clubhead through the impact zone in order to loosen their muscles.
Jeff.
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Post by gmbtempe on Dec 16, 2011 16:15:46 GMT -5
Thanks for the update, nmgolfer! Jeff, I would submit that all those golfers are throwing the clubhead into the ball, but the collision slows the clubhead down considerably. I believe if they swung just as hard in a practice swing the left wrist would likely bend immediately after low point. Considerably? I have a hard time believing that. I think we could use baseball studies on this one because the a baseball is moving at 90mph and it would slow the bat down considerably in comparison to a golf ball at rest. I dont think it has much impact at impact on the club
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Post by natep on Dec 16, 2011 16:28:23 GMT -5
There's no question that the clubhead slows down a lot, almost instantly. Even Homer worked out the math on this I believe. If the clubhead doesnt decelerate then that means that no energy, or force, or whatever it is, is transferred to the ball. I dont think its unreasonable to think that Dustin Johnson might be accelerating the club past low point, if he took a full, hard swing with no ball there. If so, he would have a much greater overtaking rate than if he actually hit a ball, slowing the clubhead down. Even if he doesnt accelerate past low point, the overtaking rate would be faster IMO.
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Post by gmbtempe on Dec 16, 2011 16:40:25 GMT -5
There's no question that the clubhead slows down a lot, almost instantly. Even Homer worked out the math on this I believe. If the clubhead doesnt decelerate then that means that no energy, or force, or whatever it is, is transferred to the ball. I dont think its unreasonable to think that Dustin Johnson might be accelerating the club past low point, if he took a full, hard swing with no ball there. If so, he would have a much greater overtaking rate than if he actually hit a ball, slowing the clubhead down. Even if he doesnt accelerate past low point, the overtaking rate would be faster IMO. I would have to see numbers, what is "a lot", half the energy, 5% of it?
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Post by natep on Dec 16, 2011 16:44:12 GMT -5
I've read it before, its like 20-30% I think. I'll have to look it up again. EDIT: I found this, it says an average club will decelerate 20-22% due to impact. It might be explained in Physics of Golf. It's in TGM too somewhere in ch.2 I think, although I think Homer might have made some mistakes thinking that if you could avoid deceleration you would hit it further. I'm pretty sure the science says it has to decel in order to transfer the energy. nventix.com/faq.html
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Post by natep on Dec 16, 2011 21:43:09 GMT -5
Here's Tapio's measurements. The yellow line is clubhead speed.
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