A HELPING HAND

[azgolfer]

Mandrin,

I'm curious if you have a model that would explain the increase in angle between the clubshaft and the left arm from the top to when the hands are at waist level. My theory is that a throwing motion means the arms and hands are relaxed and fall as the weight is transferred to the left leg. The club flattens and wants to resist moving (in this case AWAY from the target to start the swing). With the hands relaxed, this inertia causes more wrist cock, and angle between shaft and arm.

The other thing I was thinking about was that the downward motion of the clubhead is converted into a rotation, starting about waist high. This seems to be lost in 2D models. With the hands at about waist high, the right arm 'throws' the club at the ball from inside, which causes the shaft to rotate and squares the face. An example would be Vijay's right hand, where halfway down, he is converting the downward motion to a rotational motion, to the point that it gets away from his right hand and he loses his grip at impact.

Thoughts ?

 

[mandrin]

drop and catch

Mandrin,

I'm curious if you have a model that would explain the increase in angle between the clubshaft and the left arm from the top to when the hands are at waist level. My theory is that a throwing motion means the arms and hands are relaxed and fall as the weight is transferred to the left leg. The club flattens and wants to resist moving (in this case AWAY from the target to start the swing). With the hands relaxed, this inertia causes more wrist cock, and angle between shaft and arm.

The other thing I was thinking about was that the downward motion of the clubhead is converted into a rotation, starting about waist high. This seems to be lost in 2D models. With the hands at about waist high, the right arm 'throws' the club at the ball from inside, which causes the shaft to rotate and squares the face. An example would be Vijay's right hand, where halfway down, he is converting the downward motion to a rotational motion, to the point that it gets away from his right hand and he loses his grip at impact.

Thoughts ?

azgolfer,

Have a look at figs 1b and 2b in the ‘bio servo control’ thread. It depicts the inertial torque developed in the down swing. Notice it first being positive and than reversing and going negative. The initial positive torque would have been substantially greater if a dynamic transition, the inertial recoil, had been incorporated.

As a result in any down swing there is first a tendency to increase the wrist cock but once speed increases it is the centrifugal force which starts to dominate and the resulting inertial torque now strives to decrease the wrist cock.

You can think of above as quite general and applying to any type of swing, hence even if you use a more gravity oriented down swing. In a gravity type down swing however, by definition, the muscles are much more relaxed. Therefore the inertial torque has much more influence to potentially increase the wrist cock.

In a gravity type downswing swing automatically one emphasizes more the vertical direction and way less the concept of an inclined plane. Letting it drop vertically behind you and then at the last moment whip it through through impact with the pivot.

Brian in some recent post used the interesting expression, ‘drop it and catch it with the pivot’ referring to letting arms/club drop from the top and catching it with the pivot redirecting it through impact.

I continuously fool around with these things and using gravity, making the down swing like a controlled fall invariably gives me the largest speed for the clubhead. Try as an interesting experiment, from the top, to let both elbows collapse and see what happens.

Going away from a 2D plane model and favoring the vertical followed by a core rotation about vertical axis, hence truly a 3D model, involves mechanisms such as changing direction and shortening the swing radius. Think of sharply going around a corner. I always felt that there are different and perhaps better ways than swinging using a simple circular motion along an inclined plane.

 

[mandrin]

bogus?

[SIZE=-2]Conservation of Energy is what happens at the ball.
Part1. Angular momentum is about what happens on the way to the ball. [/SIZE]

Very peculiar statements. The simple scientific truth is that effort expended by the golfer from the top creates motion and associated with it there is generated simultaneously kinetic energy and angular momentum. The angular velocities increase as the downswing proceeds and with it also the kinetic energy and the angular momentum.

[SIZE=-2]The longer you sustain the lag, the smaller the wheel, and like the ice skater pulling in her arms, the faster the clubhead mass must travel to conserve angular momentum.[/SIZE]

Angular momentum is not conserved in a golfer’s downswing since there is not any to be conserved to start with. It is being generated throughout the downswing by the effort expended by the golfer. Whilst being continuously generated it is redistributed due to unfolding of the club.

In Part2 impact interval is discussed and golf2much states that much of the kinetic energy of the clubhead is transferred to the ball and formulates this as:

[SIZE=-2](½ m1*v1^2 - losses) (clubhead) = ½ m2*v2^2 (ball)[/SIZE]

where the losses are referring to the small losses due to deformation of the ball and the clubface during impact. This formulation is erroneous. The clubhead still has an appreciable velocity after impact and the formulation should have been:

[SIZE=-2]½ m1*v1^2 (clubhead) = ½ m1*u1^2 (clubhead) + ½ m2*u2^2 (ball) + losses [/SIZE

I appreciate your clarifications to the final formula... you are quite correct.

As to the balance of the discussion, my points were directed to questions that clearly had the role of momentum and kinetic energy confused. I was trying to explain the difference, simply with the point being pretty much what you already said. However, the concept that angular monentum is not conserved because there was none to start with, seems a bit bogus. Angular momentum is generated and "redistributed"(your word) during the downswing. "Redistribution" = conservation, no? The consideration I was trying to explain is the big circle (initial downswing), small circle (release) and how the greater the difference between (later release) them the greater the clubhead speed and associated kinetic energy. The second part of the discussion about kinetic energy was to explain that kinetic energy was the appropriate mechanism for energy(not momentum) transfer to the ball and how maximixing clubhead speed in step 1 resulted in greater ball speeds and greater distances.

If you think about this in very simple terms, if you attempt to influence impact, it will be over before you can do so. Thus, the angular momentum created during the downswing by maximizing lag (the diameter of the small circle) IS about what happens on the way to the ball. How fast the ball flies away is a direct result of maximizing the efficiency of this effort. What happens after the ball is gone is of no consequence to the ball, so Kinetic energy transfer is about what happens AT the ball.

Were I trying to explaing this to someone with a rigorous scientific background such as yours, I would have proceeded differently, but thanks for the clarification.

G2M

g2m,

I am very much aware that it is very demanding to discuss science in down to earth terms, but trying to explain science in very relaxed terms does not mean being inexact.

“However, the concept that angular momentum is not conserved because there was none to start with, seems a bit bogus.”

Conservation in science means that a measurable property, such as mass, energy or momentum, etc., remains constant in a closed system over time. Defining elements: closed system and property to be conserved remaining constant. In a golfer’s down swing neither of these two conditions are satisfied. Next time you think my ideas to be somewhat bogus better do a bit of homework first.

“If you think about this in very simple terms, if you attempt to influence impact, it will be over before you can do so.”

This suggests strongly that you don’t agree with HK in 2-E. It implies in effect that you can’t resist club head impact deceleration.

“The second part of the discussion about kinetic energy was to explain that kinetic energy was the appropriate mechanism for energy (not momentum) transfer to the ball and how maximixing clubhead speed in step 1 resulted in greater ball speeds and greater distances.

If you think about this in very simple terms, if you attempt to influence impact, it will be over before you can do so. Thus, the angular momentum created during the downswing by maximizing lag (the diameter of the small circle) IS about what happens on the way to the ball. How fast the ball flies away is a direct result of maximizing the efficiency of this effort. What happens after the ball is gone is of no consequence to the ball, so Kinetic energy transfer is about what happens AT the ball. “

I am afraid I don’t understand above. Using simple language should lead to easier understanding not the other way around. Try again, it isn’t easy to popularize science.

 

[golf2much]

Poor Choice of Words

"I am very much aware that it is very demanding to discuss science in down to earth terms, but trying to explain science in very relaxed terms does not mean being inexact.

“However, the concept that angular momentum is not conserved because there was none to start with, seems a bit bogus.”

Conservation in science means that a measurable property, such as mass, energy or momentum, etc., remains constant in a closed system over time. Defining elements: closed system and property to be conserved remaining constant. In a golfer’s down swing neither of these two conditions are satisfied. Next time you think my ideas to be somewhat bogus better do a bit of homework first."



My only point was that you used the word "redistributed, and I used the word "conserved", with respect to angular momentum, both to my reading meaning "equal" on both sides of the equation with the point of differentiation being impact. Bogus was a poor choice of words, perhaps I could have chosen more wisely. Considered in that contect, I think we have both said, somewhat imprecisely on my part, the same thing.

G2M

 

[golf2much]

Not Quite

“If you think about this in very simple terms, if you attempt to influence impact, it will be over before you can do so.”

This suggests strongly that you don’t agree with HK in 2-E. It implies in effect that you can’t resist club head impact deceleration.

Not quite what I said, but I see your point. The club should still be accelerating at impact, with maximum velocity reached at low point, or past the ball and after impact. Certainly, the clubhead will decelerate as a result of impact, but the degree to which you maintain the acceleration through impact, you can minimize impact deceleration. The point I was making was about thoughts of "doing something" AT impact. Doing something in the 4/10000ths of a second precisely at impact is not something the human machine is capable of doing repeatedly.

So, yes, I agree that you cannot resist impact deceleration by doing something at impact, but you can minimize impact deceleration by maximizing acceleration through the impact interval. Semantics perhaps, but this is my interpretation of what HK meant.

G2M

 

[mandrin]

[size=-2]“If you think about this in very simple terms, if you attempt to influence impact, it will be over before you can do so.”

This suggests strongly that you don’t agree with HK in 2-E. It implies in effect that you can’t resist club head impact deceleration.

Not quite what I said, but I see your point. The club should still be accelerating at impact, with maximum velocity reached at low point, or past the ball and after impact. Certainly, the clubhead will decelerate as a result of impact, but the degree to which you maintain the acceleration through impact, you can minimize impact deceleration. The point I was making was about thoughts of "doing something" AT impact. Doing something in the 4/10000ths of a second precisely at impact is not something the human machine is capable of doing repeatedly.

So, yes, I agree that you cannot resist impact deceleration by doing something at impact, but you can minimize impact deceleration by maximizing acceleration through the impact interval. Semantics perhaps, but this is my interpretation of what HK meant.

G2M[/size]

G2M, you seem to be interested in the subject hence let’s pursue our discussion a bit further.

The club should still be accelerating at impact, with maximum velocity reached at low point, or past the ball and after impact.

Not quite true. Maximum velocity goes together with zero acceleration. Hence close to impact there is virtually no acceleration of the clubhead. Any appreciable acceleration of clubhead at impact indicates an inefficient swing.

Certainly, the clubhead will decelerate as a result of impact, but the degree to which you maintain the acceleration through impact, you can minimize impact deceleration.

Not true. You can’t really maintain clubhead acceleration through impact; it is for al practical purpose totally negligible. Moreover it is not possible to decelerate and accelerate an object at the same time. Let's assume however that you meant effort expended by the golfer through impact.

The point I was making was about thoughts of "doing something" AT impact. Doing something in the 4/10000ths of a second precisely at impact is not something the human machine is capable of doing repeatedly.

Let’s get this straight to avoid semantic problems. Nobody is capable of just doing something for only 4/10000ths sec. But if one keeps exerting a force through the shaft onto the clubhead this force will than also be present during this extremely small impact interval.

So, yes, I agree that you cannot resist impact deceleration by doing something at impact, but you can minimize impact deceleration by maximizing acceleration through the impact interval. Semantics perhaps, but this is my interpretation of what HK meant.

Not true. Once impact occurs the very large inertial forces are at work, likely peaking up to about 2000, 3000 lbs. Are you seriously trying to convince me that you are producing forces with can compete with these huge inertial forces, even if only to a small measure?

G2M, I would love to hear from you how exactly you are going about to prevent deceleration of the clubhead through impact. Why not also give me something more than just arguments, for instance, some calculations to give a more convincing quantitative touch to your arguments.

 

[ThinkingPlus]

Interesting Work (No Pun Intended)

I thought this might be appropriate to post in this thread. Seems like some interesting work these folks did: http://www.jssm.org/vol4/n4/17/v4n4-17text.php#1

Enjoy!

 

[golfbulldog]

off thread topic but interesting article

If interested in the paper referenced above i suggest saving it as PDF file and reading it that way - easier to print out.

I hope it is ok to discuss this on forum - the author is academic with no financial interst in any other place...

Purpose of discussion is to compare and contrast the authors conclusions( based on measurements from real-life golfers( using those motion analysis systems with reflective markers) with TGM and Brians philosophy.

I think that again Brian will like the real life data!

Some of his conclusions ( listed in his discussion) were as follows:-

Scratch handicap players have a smaller downswing hand radius than high handicappers - this has equivalent in TGM terms with straight line delivery path( this Straight line term can be decieving!) and is clearly visible in the "sweetpivot" video Brian showed transforming one of his students.( smaller radius not straight line)

"the notion of delayed wrist motion to generate clubhead velocity is valid, however the mechanism to achieve it is based upon the path of the hands and the initial wrist angle, not a retading wrist torque" - seems to say that max trigger delay and staright line delivery( smaller hand downswing radius) go well together. Don't try to hold that lag! Do something with the hands to make sure the wrist cock does not evaporate too soon.

will let others read and digest... i know Mandrin loves that "straight line delivery" stuff - old threads....

 

[golfbulldog]

"Description of the swing mechanics

The following description the golf swing is offered as an aide to understanding the fundamental mechanics involved. The description is from the top of the backswing through impact based upon data from the scratch golfer.

The downswing is initiated with a pulling along the shaft while simultaneously applying a
positive alpha (swing) torque resulting in positive linear and angular work being done. As the club head moves away from the body, the action of the linear forcebecomes less directed at speeding up the club and more toward controlling the path of the grip point. About the time the club becomes vertical in the downswing, the alpha torque increases in magnitude as it takes over the acceleration of the club from the linear force. Simultaneously, the gamma (rolling) torque is initiated to square up the club head for impact, and a beta torque is applied to pitch the club forward. From this position up until the club shaft is roughly parallel with the ground, all the torque components increase smoothly and reach
their maximum values. From the parallel position to impact, which coincides with the increase in swing motion of the wrists, the torque components rapidly decrease. All the torque components pass through zero at or near impact resulting in maximum angular work just before impact. By the time impact is reached, the linear force is maximized and perpendicular to the path of the club head in the plane of the swing. At this time the linear force is reacting to the centrifugal loading of the club thus maximizing the linear work at impact.

Just before impact the wrists momentarily approximate a “free hinge” configuration as the golfer merely holds on to the club as its momentum carries it to impact. By the time impact is reached, all torque components are in opposite directions because the wrists cannot keep up with the rotational speed of the club at this time in the downswing. The club head does not slow down however, as the straightening of the shaft continues to accelerate the club head. The club head swing plane deflection component passes through zero at impact releasing about half of the shaft stored strain energy, and resulting in the club head velocity peaking exactly at impact.

This subject exhibited a swing hub curve with a large initial radius of curvature that decreased continuously during the downswing. He also had a highest degree of initial wrist cocking. Together, these served to reduce the initial centrifugal acceleration which in turn diminished the tendency of the club to move outward even though a positive alpha torque was applied from the initiation of the downswing. This large radius path was carried through most of the downswing as the hand speed was increased by the linear force. Approaching impact, the hub radius was quickly reduced by a redirection of the linear force, which in turned caused a rapid increase in the centrifugal acceleration. This action which was coordinated with a large increase in alpha torque, pulled the club outward and through impact. These coordinated actions give the impression of a consciously delayed wrist motion. It is believed that this sequence of events are necessary to yield the optimum segmental addition, thus the largest possible club head velocity."

This is the authors summary

I have highlighted the bits that sound familiar but can not claim a deep appreciation of the physics elements.

I believe that the alpha, beta, gamma torques refer to forces acting in the 3 planes of movement.

It is interesting to see that there is "free hinging" at impact.

That clubhead continues to accelerate after impact due to shaft changes ( this may cause problems for Mandrin?? maybe - if i understood his previous posts - just in case i got it wrong - throw in a few smilies that should keep him sweet!)

 

[golf2much]

Not Gone Away

Haven't gone anywhere, just trying to decide how much effort I want to put into this thread.

Mandrin;

Without developing an entire mathematical argument, which quite frankly may be beyond the capabilities of my Engineering(not physics) Masters Degree educated brain, the point I was making was as follows:

With the iron swing, acceleration dv/dt should reach zero at low point, and thus maximum velocity is achieved at low point, or just after impact. The positive component of acceleration at impact offsets, albeit slightly, the deceleration associated with impact. I think all that was intended by the language of 2E was to impart the concept to "drive" (my word) through impact. With a driver swing, where the ball is significantly closer to the low point of the swing, dv/dt is smaller, and possibly zero. In this case the impact deceleration is as you have described.

G2M

 

[Brian Manzella]

The post below is from MANDRIN.

I deleted it, becuase i juust needed to edit it, but our software upgrade was inprogress and I was unable to do so. Please except my apologies.

Running out of steam

I have the impression that ThinkingPlus and golf2much have run out of steam and have withdrawn, quietly and comfortably somewhere else.

Both claim to have several degrees in Engineering but yet had to excuse themselves for several basic errors made in their science posts.

Oh well, for some science is like poetry, very malleably. Knowing that most are not really science addicts, they tend to take it a bit ‘easy’.

 

[mandrin]

That clubhead continues to accelerate after impact due to shaft changes ( this may cause problems for Mandrin?? maybe - if i understood his previous posts - just in case i got it wrong - throw in a few smilies that should keep him sweet!)

Golfbulldog, I appreciate the smilies likely indicating that you are a very gently bulldog indeed. Let’s cite however a more complete sentence to keep things fair and more readily understood.

“By the time impact is reached, all torque components are reversed thus doing negative work simply because the wrists cannot keep up with the rotational speed of the club at this time in the downswing. The club head does not slow down however, as the straightening of the shaft continues to accelerate the club head. The clubhead deflection passed through zero at imapct releasing about half of the shaft stored strain energy, and resulting in the club head velocity peaking exactly at impact.”

Nesbit/Serrano use three translational joints and three revolute joints to drive their club model. These are rigid elements. The golfer’s hands however are not rigid and interface the grip with soft biomechanical tissues. That makes a huge difference.

Put a driver in a vice and notice how remarkable long it will remain vibrating. Now put the club in the hands of someone instructed to keep a reasonable tight grip and try to oscillate the club. No way. Very simple demonstration and convincing proof.

The interface with the hands constitutes a substantial over damping of the oscillatory features of the golf shaft. One can also discuss this in terms of mechanical interface impedance between hands and shaft as being very soft.

All the sales hype about loading the shaft and it whipping/kicking forward, the frequency matching of shafts, it is all based on the behavior of a shaft as if being clamped in a vice. There is just only small problem – in a golf swing it is not.

Nesbit/Serrano mention the clubhead to return to its undeflected position near impact. Golf club experts/photographic evidence however will show that the shaft bends forward at impact. Not due to a forward kicking of the shaft but due to an inertial torque caused by the centrifugal force acting through the offset center of mass of the clubhead.

In short, an overdamped mechanical oscillatory sytem can’t be loaded with strain energy to be released as kinetic energy. However, let’s consider, just for arguments sake, that the approach and conclusion about the golf club by Nesbit/Serrano are correct. However they do mention:

“The amount of strain energy absorbed and then released during the down swing is a very small percentage of the work transferred to the club.”

Hence, for all practical purposes, their very sophisticated shaft bending modeling can be considered to be a bit of an academic exercise, likely done for completeness and since their very sophisticated commercial modeling software package readily allowed it.

Golfbulldog, one has to be alert when reading scientific texts. For example, if you read in a scientific text that when you jump, the earth is being displaced, it is perfectly correct, but would you put much value in such statement?

References:

Nesbit S, ‘A Three Dimensional Kinematic and Kinetic Study of the Golf Swing’.
JSSM-2005,Vol. 4, Issue 4, 499-519

Nesbit S and Serrano M, ‘Work and Power Analysis of the Golf Swing’.
JSSM-2005,Vol. 4, Issue 4, 520-533

 

[azgolfer]

I believe that the alpha, beta, gamma torques refer to forces acting in the 3 planes of movement.

I think (roughly) the alpha is the inside out motion, the beta is the 'swing plane' and the gamma is the rotation of the clubface. The origin seems to be based on the club at address, with the z axis through the shaft, the x axis on the clubface and the y axis the target line.

From the article
"the gamma component is the roll angular motion about the long axis of the shaft."

It seems this is where the clubhead is squared, and where the swing radius decreases as well.



"About the time the club becomes vertical in the downswing, the alpha torque increases in magnitude as it takes over the acceleration of the club from the linear force. Simultaneously, the gamma (rolling) torque is initiated to square up the club head for impact, and a beta torque is applied to pitch the club forward. From this position up until the club shaft is roughly parallel with the ground, all the torque components increase smoothly and reach
their maximum values"

This seems to describe a delayed hitting action, from the inside out.

Hope they do a follow up with some PGA players.

 

[mandrin]

Haven't gone anywhere, just trying to decide how much effort I want to put into this thread.

Mandrin;

Without developing an entire mathematical argument, which quite frankly may be beyond the capabilities of my Engineering(not physics) Masters Degree educated brain, the point I was making was as follows:

With the iron swing, acceleration dv/dt should reach zero at low point, and thus maximum velocity is achieved at low point, or just after impact. The positive component of acceleration at impact offsets, albeit slightly, the deceleration associated with impact. I think all that was intended by the language of 2E was to impart the concept to "drive" (my word) through impact. With a driver swing, where the ball is significantly closer to the low point of the swing, dv/dt is smaller, and possibly zero. In this case the impact deceleration is as you have described.

G2M

Haven't gone anywhere, just trying to decide how much effort I want to put into this thread.
Golf2much, glad to see you found it worthy of your interest.

Without developing an entire mathematical argument, which quite frankly may be beyond the capabilities of my Engineering (not physics) Masters Degree educated brain, the point I was making was as follows:
Engineers also better be rigorous otherwise skyscrapers, airplanes, bridges and golf clubs would be not safe.

With the iron swing, acceleration dv/dt should reach zero at low point, and thus maximum velocity is achieved at low point, or just after impact. The positive component of acceleration at impact offsets, albeit slightly, the deceleration associated with impact.
Not true. The acceleration existing at the precise moment of onset of impact is of no consequence. Only the instantaneous velocity counts. One can not in any discernable way resist impact deceleration.

I think all that was intended by the language of 2E was to impart the concept to "drive" (my word) through impact...
The idea in 2E is just not some innocent poetry but reflects a very persistent and strong intuitive notion solidly implanted in the minds of many golfers and teachers alike.

This idea is expressed in various ways such swinging one’s weight into the ball or swinging slowly and ‘heavily’. It is supposed to increase the effective mass of the club head, resisting impact deceleration, etc. What I would love to see is some solid evidence by those who believe in these ideas. I do not, but am always open to reasonable arguments.

 

[golfbulldog]

Thanks Mandrin

Keeping you busy

ALways interesting to read your rigorous interpretation of science. Your argument is clear to understand.

Does there concept of torque application fit in with your thoughts / models. In your models ( as previously referenced above Bioservo control 1 and 2) are you operating dual pendulum in 2D space?

How are your graphs of torque application comparable to those of Nesbit?( alpha, beta , gamma components)

Thanks

 

[mandrin]

Keeping you busy

ALways interesting to read your rigorous interpretation of science. Your argument is clear to understand.

Does there concept of torque application fit in with your thoughts / models. In your models ( as previously referenced above Bioservo control 1 and 2) are you operating dual pendulum in 2D space?

How are your graphs of torque application comparable to those of Nesbit?( alpha, beta , gamma components)

Thanks

The alpha torque should be similar in nature to the inertial torque as shown in ‘bio servo control’. However it is not. Nesbit’s alpha torque also does not agree either with findings by Jorgensen and Milburn.

Golfbulldog, this type of research by Nesbit is very complex indeed and I would feel much more comfortable if an independent research effort would show similar results. Up till then I have my reservations.

 

[golf2much]

What did Kelley REALLY say?

Mandrin;

Before launching another post about what HK meant in 2E, I decided that it would be a good idea to read it again….. I have reproduced below, the first 3 paragraphs from the 6th edition, page 25 if you want to verify.

2-E. CONSERVATION OF MOMENTUM Two colliding bodies cannot separate at a speed greater than the speed of approach.

The proportion of the separation rate to the approach rate expresses the elasticity involved, and is called the Coefficient of Restitution which is 80% for the better golf balls --- but drops below 70% at high speeds. Of course, this is assuming there is no Compression Leakage (2-C-0).

This means that even with precise geometrical alignments the ball will not separate from the club at more than 80% of their approach speed. That produces, roughly, this condition – the Clubhead approaching impact at 100MPH has slowed to 80MPH at separation. The ball leaves the Club at 70MPH (70% of 100 MPH approach speed). To do this, the ball must be traveling 150MPH. If the Clubhead speed at separation is 40MPH, the ball can only travel 110MPH under this law. Notice this – the ball acquires on 70% of the Clubhead “approach” speed (so there must be speed), but 100% of the Clubhead “separation” speed (so there must be resistance to deceleration). Zero Deceleration is what would give maximum ball speed for any and all approach speeds. Speed (Centrifugal Pull), and Prestress (Acceleration) stiffen the Clubshaft for consistent (minimum to maximum) resistance to Impact Deceleration. Treat that “heavy” feel of “Clubhead recovery” after impact as though it were all Impact, even though the ball is actually long gone.

I think, that if read carefully, you will find that Kelley makes a clear distinction between Deceleration and Impact Deceleration. The specific phrase "so there must be resistance to deceleration" is not in reference to the golfer doing something to resist impact deceleration, but in reference to the golfer doing something to avoid one of the 4 snares, quitting. Impact Deceleration is something he recongized as unavoidable in the early language of the 2nd paragraph. In the final sentence of the paragraph he advised; "Treat that “heavy” feel of “Clubhead recovery” after impact as though it were all Impact, even though the ball is actually long gone." as guide to the golfer to maintain his drive/acceleration/thrust all the way through impact, a swing thought if you will, not a physics statement. I think the final sentence in the 2nd paragraph makes it quite clear that he understood and made a concious distinction between ordinary Deceleration and Impact Deceleration.

Sorry for such a long post, but I'm not sure we have anything more to debate. Certainly, the golfer can resist ordinary deceleration by simply not quitting; impact deceleration on the other hand, you have no control over.

G2M

 

[mandrin]

Homer Kelley not quite up to par

[size=-2]Mandrin;

Before launching another post about what HK meant in 2E, I decided that it would be a good idea to read it again….. I have reproduced below, the first 3 paragraphs from the 6th edition, page 25 if you want to verify.

2-E. CONSERVATION OF MOMENTUM Two colliding bodies cannot separate at a speed greater than the speed of approach.

The proportion of the separation rate to the approach rate expresses the elasticity involved, and is called the Coefficient of Restitution which is 80% for the better golf balls --- but drops below 70% at high speeds. Of course, this is assuming there is no Compression Leakage (2-C-0).

This means that even with precise geometrical alignments the ball will not separate from the club at more than 80% of their approach speed. That produces, roughly, this condition – the Clubhead approaching impact at 100MPH has slowed to 80MPH at separation. The ball leaves the Club at 70MPH (70% of 100 MPH approach speed). To do this, the ball must be traveling 150MPH. If the Clubhead speed at separation is 40MPH, the ball can only travel 110MPH under this law. Notice this – the ball acquires on 70% of the Clubhead “approach” speed (so there must be speed), but 100% of the Clubhead “separation” speed (so there must be resistance to deceleration). Zero Deceleration is what would give maximum ball speed for any and all approach speeds. Speed (Centrifugal Pull), and Prestress (Acceleration) stiffen the Clubshaft for consistent (minimum to maximum) resistance to Impact Deceleration. Treat that “heavy” feel of “Clubhead recovery” after impact as though it were all Impact, even though the ball is actually long gone.

I think, that if read carefully, you will find that Kelley makes a clear distinction between Deceleration and Impact Deceleration. The specific phrase "so there must be resistance to deceleration" is not in reference to the golfer doing something to resist impact deceleration, but in reference to the golfer doing something to avoid one of the 4 snares, quitting. Impact Deceleration is something he recongized as unavoidable in the early language of the 2nd paragraph. In the final sentence of the paragraph he advised; "Treat that “heavy” feel of “Clubhead recovery” after impact as though it were all Impact, even though the ball is actually long gone." as guide to the golfer to maintain his drive/acceleration/thrust all the way through impact, a swing thought if you will, not a physics statement. I think the final sentence in the 2nd paragraph makes it quite clear that he understood and made a concious distinction between ordinary Deceleration and Impact Deceleration.

Sorry for such a long post, but I'm not sure we have anything more to debate. Certainly, the golfer can resist ordinary deceleration by simply not quitting; impact deceleration on the other hand, you have no control over.

G2M[/size]

golf2much, since you invited me to have a careful look at Kelley’s ideas, I did have indeed a closer look. But you might not appreciate my analysis.

HK – “ The proportion of the separation rate to the approach rate expresses the elasticity involved, and is called the Coefficient of Restitution which is 80% for the better golf balls --- but drops below 70% at high speeds. Of course, this is assuming there is no Compression Leakage (2-C-0).”

m - The phrase ‘The proportion of the separation rate to the approach rate’ is quite confusing; should have been instead ‘The ratio of relative velocities before and after impact’.

Morover, elasticity is not the correct word to invoke when referring to the coefficient of restitution. The coefficient of restitution does not relate to elasticity but rather to kinetic energy loss, due to a variety of mechanisms, such as, permanent deformation, generation of heat and sound.

HK – “This means that even with precise geometrical alignments the ball will not separate from the club at more than 80% of their approach speed. That produces, roughly, this condition – the Clubhead approaching impact at 100MPH has slowed to 80MPH at separation. The ball leaves the Club at 70MPH (70% of 100 MPH approach speed). To do this, the ball must be traveling 150MPH.”:

m - Let’s verify above with the relations governing impact:

(V-V’)=M2/M1 *U’, (rel1) and (U’-V’)=e*V, (rel2)

where V, V’ speed of clubhead resp. before and after impact, U’ separation speed of ball, M1 mass of clubhead and M2 mass of ball and e coefficient of restitution.

From rels1&2 one can derive:

U’=(1+e) M1/(M1+M2)*V (rel3) and V’=(M1-e*M2)/(M1+M2)*V (rel4)

We assume the clubhead mass M1 for a persimmon driver to be somewhere between 160 and 200 gr; Furthermore e=0.7 and M2=46 gr.

With V=100mph and M1 either 160 or 200 gr one obtains U’=132/138 mph and V’=62/68 mph. That does not fit at all with HK’s value U’=150 mph and V’=80mph.

HK – “If the Clubhead speed at separation is 40MPH, the ball can only travel 110MPH under this law. “

With V=100mph and M1 either 160 gr or 200 gr one obtains again, as above, U’=132/138 mph and V’=62/68 mph. That does not fit at all with HK’s U’=110 mph and V’= 40 mph.

Impact is governed by two equations and three variables. HK’s basic error is to use a single equation to propose various scenarios. Once the clubhead speed V is known than V’ and U’ are determined by the governing equations and can’t be arbitrarily chosen anymore as by HK.

HK – - Notice this – the ball acquires on 70% of the Clubhead “approach” speed (so there must be speed), but 100% of the Clubhead “separation” speed (so there must be resistance to deceleration). Zero Deceleration is what would give maximum ball speed for any and all approach speeds. Speed (Centrifugal Pull), and Prestress (Acceleration) stiffen the Clubshaft for consistent (minimum to maximum) resistance to Impact Deceleration.

g2m – I think, that if read carefully, you will find that Kelley makes a clear distinction between Deceleration and Impact Deceleration. The specific phrase "so there must be resistance to deceleration" is not in reference to the golfer doing something to resist impact deceleration, but in reference to the golfer doing something to avoid one of the 4 snares, quitting. Impact Deceleration is something he recongized as unavoidable in the early language of the 2nd paragraph.

m – golf2much, I am afraid that I have to give to give you 0 for reading/comprehension skill. It is very clear from the text that HK wants to say exactly the opposite of your interpretation.

Basically, HK states:
The clubhead decelerates at impact and the golfer when resisting this deceleration increases the ball separation speed.
Resisting such that one obtains zero clubhead deceleration results in the maximum possible ball separation speed for any clubhead speed.

The phrase re. shaft stiffness is another very clear indication implying resisting clubhead deceleration during impact interval.

HK – Zero Deceleration is what would give maximum ball speed for any and all approach speeds.

m – Zero Deceleration implies that the clubhead has the same speed before and after impact and hence can’t transfer any of its energy/momentum to the ball.

g2m – Certainly, the golfer can resist ordinary deceleration by simply not quitting; impact deceleration on the other hand, you have no control over.

m - g2m, you are now for sure in complete contradiction with TGM philosophy and very definitely also with ThinkingPlus, your science buddy. See below.

ThinkingPlus – “Lag pressure maintained through impact will result in a collision that is more inelastic (less lossy) than if one had a clubhead moving with a constant velocity (my assertion, et al.).”

Conclusions: It is very clear from above that HK did not understand the basic mechanism and rules governing collisions. Conservation of momentum is a very fundamental law in physics and HK himself said about laws – “Nor can they or anyone else be exempted from compliance with them.” I would imagine that HK meant to also include himself with that statement.

 

[golf2much]

It's OK to Disagree

Mandrin;

I always appreciate your analysis as debate and disagreement are as fundamental to the scientific process as the laws and formulas you cite. However, I have to disagree with your interpretation of the passages I quoted. I won't argue with your mathematics as they appear to be correct, and I don't think HK intended his words to be as strictly interpreted as you have done. His use of the word "roughly: clearly implies that he was estimating to make a point, that being that the clubhead decelerates at impact, and that there is a loss due to the clubhead/ball collision. So while I'm sure your math is right, it only makes the same point somewhat more precisely than the original estimate.

The written word is always subject to interpretation by the reader, and since HK prefaced his work with the proviso that when he used a word, it carried the plain, ordinary dictionary definition. With this in mind, his use of the word deceleration without the qualifier impact clearly implies a differentiation between deceleration prior to impact, and impact deceleration itself. We can argue over the interpretation til the cows come home but it serves no one.

"Basically, HK states:
The clubhead decelerates at impact and the golfer when resisting this deceleration increases the ball separation speed.
Resisting such that one obtains zero clubhead deceleration results in the maximum possible ball separation speed for any clubhead speed.

The phrase re. shaft stiffness is another very clear indication implying resisting clubhead deceleration during impact interval."

This is your interpretation of what you think Kelley meant, but not what he said.

Certainly you would agree that decelerating prior to impact would not be a good thing and that zero deceleration prior to impact would result in the maximum separation speed.

You and I have agreed previously that the golfer can do nothing during the approximately 4/10000ths of a sec impact interval, and HK while maybe not even knowing the specific duration, knew it was short. This is seen in the phrasing about treating the "clubhead recovery" as though it was all impact, even though the ball is long gone. Again, this is not a physics statement, but a swing thought to assist the reader in understanding the need to "drive through" impact to low point to insure the most efficient impact.

Also, you wrote "HK – Zero Deceleration is what would give maximum ball speed for any and all approach speeds.

m – Zero Deceleration implies that the clubhead has the same speed before and after impact and hence can’t transfer any of its energy/momentum to the ball."

I think you missed the point completely here. Zero deceleration implies maximum velocity prior to impact. You again are assuming that deceleration is related to impact deceleration, and not a deceleration in the approach speed. HK carefully used the word approach in this passage to convey exactly this meaning. If he intended to refer to impact, he would have used the word separation.

Finally, I'll give you an A+ for the use of color and neat little smiley face icons, but I suggest you study the written word and the context in which it's written before you challenge my reading comprehension. Like many brilliant and very educated scentists I have worked with in my career, you miss the essence of the words, because you're thinking in formulas.

We will likely not agree on this particular interpretation, but that's OK. I still appreciate and respect your approach.

G2M

 

[mandrin]

Fascinating & puzzling

golf2much,

I find it both fascinating and puzzling that you can see black where I see white and vice versa. So a very different approach is required to break out of this stalemate position.

You clearly agree with me that there is absolutely nothing we can do during the impact interval of 0.0004 seconds. However you are also clearly disagreeing with me on my analysis of HK’s vision and ideas on the same subject matter.

On your home turf at the top of the pyramid there is one person who is known to know HK’ ideas inside and outside. Why not ask him a few precise questions about it all. I am sure that you will trust his judgment. Suppose that he responds contrary to your believes - I am absolutely sure he will - how are you going to react?

If you don’t ask some clear questions I will have to conclude that you are not so sure after all and really don’t want to find yourself in a rather embarrassing situation.

BTW, would you be so kind to explain to me what ThinkingPlus possibly meant with,

“Lag pressure maintained through impact will result in a collision that is more inelastic (less lossy) than if one had a clubhead moving with a constant velocity (my assertion, et al.).”

and also tell me if you agree with the ideas contained in her statement.