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Post by iacas on Nov 3, 2011 7:55:26 GMT -5
Can we all agree that this principle does not apply?
Two basic reasons:
a) the golf swing is not a closed system
b) If you truly conserved angular momentum from the top of the backswing, you'd never swing down since the momentum at the top is 0.
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Brief aside: if anything, parametric acceleration has more to do with COAM (more than nothing is not exactly a high bar) than the kinematic sequence does, and yet time and time again you see people talking about COAM as the reason for proper kinematic sequencing.
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Post by Richie3Jack on Nov 3, 2011 8:08:27 GMT -5
I thought that one could not 'conserve' momentum to begin with.
3JACK
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Post by nmgolfer on Nov 3, 2011 8:43:55 GMT -5
Yes that's correct... it does not apply
COAM applies to a system that is in stasis. i.e. No forces are doing work. No energy is being added or subtracted. During the golf stroke muscles apply forces across joints causing movement and are therefore doing work (in the physics definition of the word) therefore COAM does not apply.
Momentum can be conserved. Think of a flywheel battery where in mass gets spun up to high rpm then sits there in stasis. Since the mass on its shaft is supported by low friction bearings, no energy is lost. Then when that energy is needed, the momentum can be tapped and trained off. That is a case in which momentum is conserved. Does this in any way apply to the golf stroke? NO...
It does not even help to think of momentum being conserved with respect to the golf swing. That was one of those blind alley of misconceptions book authors have led people down.
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Post by nmgolfer on Nov 3, 2011 9:20:15 GMT -5
With regards to parameteric acceleration... I'm not certain as to Prof. Muria's area of expertise but I believe his concept as expressed in that paper is derived from vibration control research. Vibration control researchers most definitely do describe parametric damping. (To damp a vibration is to reduce the magnitude of oscillation). Suppose you have a mass hanging from a flexible support like a wirerope. Its swinging like a pendulum, the wind or whatever is driving it and you don't want the oscillation to get out of control where it might break something. The way to control it is by using parametric damping. Judiciously applied force at the opportune time (i.e. parametric damping) can extract or add energy to that oscillating system. Prof. Muria took this concept and applied it to analysis of the golf swing to explain what better golfers do in that late stages prior to impact. That's all well and good. But I would argue better golfer are in effect applying parametric acceleration through out the latter two stages of the downswing (Nesbit's research shows all full swing golf strokes are characterized by three distinct phases as defined by changes in instantaneous swing center) It is the off-axis component owing to the changing radii which accelerates the clubhead in a tangential direction. That off-axis component is maximized by continually shorten the swing center radius during the last two phases of the downswing not just the last few microseconds. Ideally there is not "something different" that happens just before impact. A hitter's torque (push-pull exertion at the hands) complicates the equations but considering just the swinger's effort I believe it can be shown mathematically (as an analytical solution) that the optimal hand path is synonymous with optimal "parametric accleration" and traces a contracting spiral not unlike the one shown:  |
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Post by iacas on Nov 3, 2011 12:37:19 GMT -5
With regards to parameteric acceleration... I was hoping to draw you out on the COAM stuff. For the sake of clarity I hope to keep this thread about COAM, though, so that people searching in Google for this will find this thread and be given some ammo to counter the people who think COAM exists or is relevant in the downswing (in particular the sequencing of when hips, shoulders, etc. reach maximum speed). Then again, if everyone agrees, there's not going to be much content on that.  Thanks for your post on P.A. I specifically searched for some of your posts on COAM and included links to them in a few discussions in which I'm involved right now. |
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Post by birlyshirly on Nov 4, 2011 7:30:28 GMT -5
I understand and agree. But what are the practical implications for a golfer who doesn't?
To take an absurd example, the golfer who thinks that COAM does apply is presumably NOT going to freeze his top of the backswing position and wait for COAM to hit the ball for him.
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Post by iacas on Nov 4, 2011 9:25:35 GMT -5
To take an absurd example, the golfer who thinks that COAM does apply is presumably NOT going to freeze his top of the backswing position and wait for COAM to hit the ball for him. No, I think that golfer confuses COAM with the way our bodies work in a moderately "optimal" (swing speed) swing. They see the hips reaching maximum angular velocity, then the shoulders, then the hands, then the clubhead, and they think that the hips slowing down "speeds up" the shoulders, and the shoulders slowing down "speeds up" the hands, etc. But there are studies out there and graphs and charts of accomplished players showing that even that isn't necessarily true. Sometimes the hands don't slow down. Sometimes the angular velocity of the shoulders matches the arms for longer than some other people think they should (and maybe they shouldn't - maybe that swing isn't "optimal" for speed). Etc. |
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Post by birlyshirly on Nov 4, 2011 13:12:05 GMT -5
So, is it your feeling that a belief in COAM leads to golfers stalling or quitting on shots?
What concepts do you use to convey a better sequence of movements? Is there a sin of over-acceleration? Do you advise people to let the clubhead do the work?
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Post by iacas on Nov 4, 2011 14:38:31 GMT -5
Frankly, I just wanted to establish another thread on the Internet showing that COAM doesn't apply to the golf swing.
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Post by birlyshirly on Nov 4, 2011 14:44:11 GMT -5
Fair enough. I wouldn't argue that most golfer don't have a shaky grasp of physics. But I'm always more interested in whether these "misconceptions" result in adverse consequences.
If you want people to accept that COAM doesn't apply - then I think that people will listen and learn more readily if you show why such a misconception can hurt their golf, not just their credibility on internet boards...
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Post by iacas on Nov 4, 2011 15:41:24 GMT -5
If you want people to accept that COAM doesn't apply - then I think that people will listen and learn more readily if you show why such a misconception can hurt their golf, not just their credibility on internet boards... I understand that. But more often this comes up - for me - when discussing things with other instructors. I prefer that they not base things on junk science, even if I agree with what they're trying to say in the end. |
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Post by birlyshirly on Nov 4, 2011 18:46:05 GMT -5
Hmm. Big issue.
To my mind, lots of science is effectively junk when it's bandied around as theory - divorced from practical and discernable consequences in hitting the ball.
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Post by nmgolfer on Nov 11, 2011 11:09:46 GMT -5
Science is a process which begins with at testable hypothesis and perhaps a "mathematical" basis i.e. "the math says do this..." Suppose a golfer writes a book and says hit down with your driver. Scientist says that's crazy... the math says hit up (maximize launch angle for maximum carry). Test the hypothesis... result: all long drivers are hitting up some more than others... the science rules. Consider COAM... never-mind that it cannot apply to the golf swing because the very definition of the term is violated, just consider the mental image it conveys. It says spin like an ice-skater and you'll win the tournament... it says bring your hips then shoulders then arms to a stop then you'll maximize your CHS... The science says baloney. The science says "cracking the whip" analogies are bogus. Test the hypothesis. What do long drivers do? They certainly don't spin like an ice dancer and their swing is one continuous motion, with no discernible slowing of body parts into and through the ball. Science (the testable hypothesis) rules. Theorizing scientists need to exercise caution. If they're basing their theory on a faulty deficient math model then the results of the test are inconclusive. A faulty math model like say the double pendulum may predict one outcome that happens to coincide with the test result outcome but that does not mean the theory is validated. It simply means a bad model matched the test results. Hmm. Big issue. To my mind, lots of science is effectively junk when it's bandied around as theory - divorced from practical and discernable consequences in hitting the ball. |
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