Golf swing and playground swing

[mandrin]

Not really that interested in the shaft issue but I am curious how you would explain the difference between theoretical evidence and experimental evidence? I don't know, it may have been just "quick typing".
I.K.

Theoretical consideration predicts forward bending.
High speed video has clearly shown it to happen.
Conclusion – theory and experiment agree!

 

[EdZ]

You are primarily referring to feel and not necessarily to what actually happens.

There is a clubhead, a shaft and the hands, forming the interface between the club and the golfer.

For a driver both theoretical and experimental evidence shows that the shaft bends forward at impact. This effect is substantially less or absent with irons.

Hence for a driver the loading of the shaft, by bending, is not a potential energy which can be maintained and released at impact.

Do you hence believe that the ‘loaded bent shaft’ (driver), is a useful feel type image/instruction not necessarily corresponding to the physics involved?

What variables are you assuming Mandrin?

We agree on the physics of a flail, just not its location when applied to the human machine in a golf swing.

Unless you are trying to tell me that gravity is the key reason for this forward bending, I see no reason at all that this forward bending can't happen later than current experiments have 'assumed', by limiting their variables/perspective regarding when 'in line' happens, and specifically the ratio of loading, to unloading and acceleration over time and space within a circle (how long the 'bent' shaft is maintained and over what time force is applied and maintained).

In short, force is still being applied past the 'bottom of the circle'/perpendicular to the ground position that the 'illusion' of the left arm and club create.

Force is still being applied, 'downplane' until both arms straight. You assume it stops at perpendicular to the ground.

 

[mandrin]

What variables are you assuming Mandrin?

We agree on the physics of a flail, just not its location when applied to the human machine in a golf swing.

Unless you are trying to tell me that gravity is the key reason for this forward bending, I see no reason at all that this forward bending can't happen later than current experiments have 'assumed', by limiting their variables/perspective regarding when 'in line' happens, and specifically the ratio of loading, to unloading and acceleration over time and space within a circle (how long the 'bent' shaft is maintained and over what time force is applied and maintained).

In short, force is still being applied past the 'bottom of the circle'/perpendicular to the ground position that the 'illusion' of the left arm and club create.

Force is still being applied, 'downplane' until both arms straight. You assume it stops at perpendicular to the ground.

Ed, I feel that we are on two parallel planes, close but not quite touching.

I make a sharp distinction between impact, 0.0005 sec, and the remaining of the swing. Impact is ruled by collision theory and is totally decoupled from the golfer. He might as well not be there. Everything else, almost 100%, is the remaining of the golf swing and under ‘control’ by the golfer.

I started with impact and things rapidly bifurcated to the whole of the swing. As mentioned above, two different worlds, not to be mixed, otherwise the confusion will remain with us and will last till the end of times.

From the top, the shaft first bends inwards to the golfer. About 0.1 sec later the centrifugal force starts rapidly dominating and the shafts starts bending outward /forward. There is no spring like feature of the shaft acting in the downswing, the soft biological tissue in the hands introduce too much damping.

The large centrifugal force, acting through the offset center of mass of the club head, introduces the torque responsible for the forward bending of the shaft. This torque is readily calculated and agrees with the forward bending shown by high speed video.

Now to come more specifically to your concerns. The golfer exerts torque on the butt end of the shaft. The centrifugal force exerts also a torque, but on the clubhead end of the shaft. The total torque acting on the shaft is simply the vector sum of the two torques operating on the shaft.

Hence, even if the shaft is bent forward does not imply that the torque exerted by the hands has no effect, even if this is usually implied or suggested. Bent or not bent, the torque exerted by the hands on the butt end of the shaft is and remains effective. It is independent of a ‘bent condition’ or being ‘in line’.

However, just for that fleeting tiny little moment of 0.0005 sec during impact, the golfer, with all its good intentions, stops to exist; physics takes over and rules impact all by itself. However, only for those 0.0005 sec and then control is back again into the hands of the golfer, directing ‘force’ to aiming point, rotating, swiveling or whatever he tries to accomplish.

 

[EdZ]

Ed, I feel that we are on two parallel planes, close but not quite touching.


The large centrifugal force, acting through the offset center of mass of the club head, introduces the torque responsible for the forward bending of the shaft. This torque is readily calculated and agrees with the forward bending shown by high speed video.

Now to come more specifically to your concerns. The golfer exerts torque on the butt end of the shaft. The centrifugal force exerts also a torque, but on the clubhead end of the shaft. The total torque acting on the shaft is simply the vector sum of the two torques operating on the shaft.

Hence, even if the shaft is bent forward does not imply that the torque exerted by the hands has no effect, even if this is usually implied or suggested. Bent or not bent, the torque exerted by the hands on the butt end of the shaft is and remains effective. It is independent of a ‘bent condition’ or being ‘in line’.

OK - lets get back to the forward bending shaft. You claim this is due to offset mass and centrifugal force.

The issue isn't 'why' this happens - it is WHEN this happens.

Do you agree that at some point in the motion, the clubhead does indeed trail and the shaft is bent?

If so...

What factors do you think would change 'when' this forward bending happens?

What would it take for the torque on the butt end of the shaft to override the torque on the clubhead until 'after' impact? (for the sake of this arguement, assume 'impact location' on the circle, leaving aside the impact interval for a moment - clubhead/clubshaft action/motion only).

 

[strav]

50 odd years ago

In “Power Golf” pages 30-31, Ben Hogan wrote:
“In regard to the Clubhead and its function, most golf fans don’t realize that during the course of the ideal golf swing the clubhead is ahead of the shaft as you approach the ball. Until moving pictures showed exactly what was taking place most people imagined that the clubhead was behind the shaft”

 

[mandrin]

What variables are you assuming Mandrin?

We agree on the physics of a flail, just not its location when applied to the human machine in a golf swing.

Unless you are trying to tell me that gravity is the key reason for this forward bending, I see no reason at all that this forward bending can't happen later than current experiments have 'assumed', by limiting their variables/perspective regarding when 'in line' happens, and specifically the ratio of loading, to unloading and acceleration over time and space within a circle (how long the 'bent' shaft is maintained and over what time force is applied and maintained).

In short, force is still being applied past the 'bottom of the circle'/perpendicular to the ground position that the 'illusion' of the left arm and club create.

Force is still being applied, 'downplane' until both arms straight. You assume it stops at perpendicular to the ground.

Ed,

The time history of the torques applied by a golfer is seemingly like a finger print, very unique to each golfer. Moreover, the interaction between the two torques at both ends of the shaft is a very complex one, not prone to simple fast rules.

I have the software developed to analyze the behavior of flexible shafts and eventually will post using it. Let me give just some feeling for what is required. A pro swing will typically generate about 15 Nm (11 lb-ft) centrifugal torque, through the com offset of the clubhead, at impact.

If you clamp the but end off the shaft solidly to the table and attach a small 2lb dumbbell to the hosel you create a torque of about 6 lb-ft. Notice the considerable deflection in the driver shaft for this torque.

Let’s take two golfers. One sharply ‘loads’ the shaft and eventually allows the club coast freely through impact. The other starts very gently and aggressively pours it on towards impact. Will the shaft behave different for these to cases? That I feel is what you would like to know.

It definitely will be different for these two cases but it is not easy to give a simple answer. Can a golfer manage to swing such that he can override the forward bending due to the centrifugal torque? The video evidence seems to suggest that only forward bending takes place.

Nevertheless the way you swing definitely should have an influence on the amount of forward/backward bending occurring during the downswing. But an exact analysis is a bit more complex than taking out one’s pocket calculator.

 

[EdZ]

..........

It definitely will be different for these two cases but it is not easy to give a simple answer. Can a golfer manage to swing such that he can override the forward bending due to the centrifugal torque? The video evidence seems to suggest that only forward bending takes place.

Nevertheless the way you swing definitely should have an influence on the amount of forward/backward bending occurring during the downswing. But an exact analysis is a bit more complex than taking out one’s pocket calculator.

Understood that in a golf swing, this is a complex equation. Again, I am not saying you can completely 'override' CF, only that you can 'delay' the point in the circle that event is likely to occur via proper transition ratio, (Pi), and rate/direction of force applied.


As for video evidence, visual evidence would have most believe the world is basically flat and stationary, or that the Sun 'rises' and 'sets'.

Many variables have to be understood to show otherwise. Science is all about "questioning your assumptions" in a systematic way.

Perhaps we can simplify the conversation a bit and ponder a cracking whip motion in 2 dimensions.

A circle, with a radius moving in a whip like motion that is flexible, constant properties along its length. If the only force acting on that whip was from the center of the circle, what variables would you suggest would alter where around the circles edge the radius would be 'straight' if it were moved back/through?

Would you agree that the rates and ratio of 'backswing' to 'forward swing' forces are likely key factors?

 

[Burner]

It is commonly accepted that once the clubhead's resistance to its own inertia exceeds the torque (lag pressure) being applied at the opposite end of the clubshaft, that the shaft will adopt a forward bending aspect (Clubhead overtakes Clubshaft).

This condition, however, only obtains when the lag pressure being applied is a diminishing return - most golfers, we are led to believe, have swings that actually decelerate into impact - hence the forward bending shaft "evidence" being provided by some as scientific fact in order to prove an unsustainable belief.

However, should the lag be sustained, Homer be praised, the clubhead cannot overtake the the clubshaft and will always lag behind the impelling force applied to the shaft from above.

 

[mandrin]

Understood that in a golf swing, this is a complex equation. Again, I am not saying you can completely 'override' CF, only that you can 'delay' the point in the circle that event is likely to occur via proper transition ratio, (Pi), and rate/direction of force applied.


As for video evidence, visual evidence would have most believe the world is basically flat and stationary, or that the Sun 'rises' and 'sets'.

Many variables have to be understood to show otherwise. Science is all about "questioning your assumptions" in a systematic way.

Perhaps we can simplify the conversation a bit and ponder a cracking whip motion in 2 dimensions.

A circle, with a radius moving in a whip like motion that is flexible, constant properties along its length. If the only force acting on that whip was from the center of the circle, what variables would you suggest would alter where around the circles edge the radius would be 'straight' if it were moved back/through?

Would you agree that the rates and ratio of 'backswing' to 'forward swing' forces are likely key factors?

Ed, simplification is definitely useful but should be used with care - “Treating a complex subject or action as though it were simple, multiplies its complexity because of the difficulty in systematizing missing and unknown factors or elements.” HK.

For the case of a single flexible uniform rod, pinned to a center, the essential defining system parameters are: The elastic modulus E, the mass density, the cross-sectional moment of inertia I, and the cross-sectional area A.

In addition the initial conditions and the time history of the applied torque at the center are required. Further more do we consider the lowest natural frequency of the system or do we also consider higher natural frequencies?

One esential factor which is in this case completely evacuated is the centrifugal torque. There is however still some small centrifugal stiffening effect due to the rotation. Another very important factor is the damping very present in a real golf swing and absent in this simple model.

The behavior of this simple arrangement depends heavily on the basic natural frequency of the system and to a lesser degree on the time history of the applied torque. A mathematical analysis is required to go beyond educated guessing.

 

[Mike O]

Better

Theoretical consideration predicts forward bending.
High speed video has clearly shown it to happen.
Conclusion – theory and experiment agree!

That's better.

There is no "theoretical evidence". But of course, there is theory based on evidence- and then proved through precise experiments with the appropriate controlling factors.

 

[mandrin]

That's better.

There is no "theoretical evidence". But of course, there is theory based on evidence- and then proved through precise experiments with the appropriate controlling factors.

Mike O,

Not really that interested in your opinions about science but thought it appropriate to point out some basic errors.

Since you are so assured of your imperial scientific knowledge, I like to invite you to do a simple experiment.

Use your fingers and coordinate them appropriately to activate a mouse for a few clicks to access Google.

Type slowly and deliberately the two words ‘theoretical evidence’ and watch the many scientific articles all using the two words ‘theoretical evidence’.

This simple exercise should provide you with enough evidence that the frequent use of the expression ‘theoretical evidence’ is indeed evident.

Just one typical example:

Experimental and theoretical evidence for homogeneous catalysis in the gas-phase reaction of SiH2 with H2O (and D2O): a combined kinetic and quantum chemical study. Journal of the American Chemical Society, 126, (21), 6816-6824.

There is theory based on experiments, there is theory preceding and leading to experiments, and there is theory standing all by itself.

 

[mandrin]

However, should the lag be sustained, Homer be praised, the clubhead cannot overtake the the clubshaft and will always lag behind the impelling force applied to the shaft from above.

Burner, do you 'feel' this to be true or do you 'know' this to be true.

 

[Burner]

Burner, do you 'feel' this to be true or do you 'know' this to be true.

I would say "know" rather than "feel" purely on the grounds that something has caused the bow in the shaft which leaves the clubhead lagging behind and whilst ever that something remains constant then the bowed shaft and lagging clubhead will remain in effect.

Bit like a Horse drawn Barge. Whilst ever the pulling Horse exerts pressure on the rope then the Barge will remain (or lag) behind it.

If the Horse stops pulling, or simply slows down to the extent that the pressure on the rope slackens off, then the Barge ceases to be pulled (lag pressure is lost) and will overtake that which was pulling it (causing it to lag).

 

[mandrin]

I would say "know" rather than "feel" purely on the grounds that something has caused the bow in the shaft which leaves the clubhead lagging behind and whilst ever that something remains constant then the bowed shaft and lagging clubhead will remain in effect.

Bit like a Horse drawn Barge. Whilst ever the pulling Horse exerts pressure on the rope then the Barge will remain (or lag) behind it.

If the Horse stops pulling, or simply slows down to the extent that the pressure on the rope slackens off, then the Barge ceases to be pulled (lag pressure is lost) and will overtake that which was pulling it (causing it to lag).

Burner,

Your post is interesting and very logical but there is an important omission. You refer to one cause for the lag of clubhead and bow in the shaft. There are however two opposing causes at work.

The effective weight of the clubhead increases from 0.44 lb to about 130 lb through impact for a pro type swing. With a radius of gyration of about 1 inch this gives a fairly large torque, about 11 lb-ft, wanting to bow the shaft the other way.

It is very difficult to be aware of this large force since it last for only a very short time, too short to be really registered by our senses. On the other hand we are readily aware of the torque/force exerted by our hands on the butt end of the shaft.

Here again, as so often in golf, – feel and real don’t quite agree.

 

[Mike O]

A mess

Mike O,

Not really that interested in your opinions about science but thought it appropriate to point out some basic errors. *

*You really should study epistemology- it would give you the ability to use concepts in a precise manner. So you're going to point out "some" basic errors- hmm? Or One? or None?*

Since you are so assured of your imperial scientific knowledge, I like to invite you to do a simple experiment.

Use your fingers and coordinate them appropriately to activate a mouse for a few clicks to access Google.

Type slowly and deliberately the two words ‘theoretical evidence’ and watch the many scientific articles all using the two words ‘theoretical evidence’.

This simple exercise should provide you with enough evidence that the frequent use of the expression ‘theoretical evidence’ is indeed evident.**

**I was never stating the term was not used? But hey, nice job since you pointed out something that we weren't even discussing? You've provided evidence that people use the term-way to stay on topic! Or maybe you stayed on topic- assuming that the standard you use to validate a concept is "how many other people use it"- hope that wasn't the case- as you'd be worse off than I thought.**

Just one typical example:

Experimental and theoretical evidence for homogeneous catalysis in the gas-phase reaction of SiH2 with H2O (and D2O): a combined kinetic and quantum chemical study. Journal of the American Chemical Society, 126, (21), 6816-6824.

There is theory based on experiments, there is theory preceding and leading to experiments, and there is theory standing all by itself.***
*** Here you go again- please stay on topic- we're talking about the proper use of the concept evidence and if the sub-concept "theoretical evidence" is a proper concept. And it's not.

A theory is a set of abstract principles purporting to be either a correct description of reality or a set of guidelines for man's actions. Anotherwords, it's dealing with concepts that are extremely far up the conceptual chain- concepts from concepts from concepts- but all based on reality and ultimately retraceable to their roots in reality i.e. those things perceived from your senses.

Evidence is a concept that is at the bottom end of the conceptual chain- less steps away from the source of all concepts- perceptual reality- i.e. the senses. It's the data that you would use to confirm the theory.

You can have a lot of sub-concepts for evidence- see the law field- that are valid concepts- i.e evidence sub-categorized into it's source- testimony, visual, etc. But the term "theoretical evidence" is really a contradiction in terms.

See my comments above-
You've got a very confusing post- even though you don't want to hear "my opinion"- you really should study epistemology It's apparent that you have no grasp of it and it's hurting your "logic"- As the 2nd branch of philosophy- it is the science devoted to the discovery of the proper methods of acquiring and validating knowledge- and it is the foundation that every other field of science rests on- and therefore your lack or grasp of it- determines your success in any particular field.

 

[mandrin]

amusing

See my comments above-
You've got a very confusing post- even though you don't want to hear "my opinion"- you really should study epistemology It's apparent that you have no grasp of it and it's hurting your "logic"- As the 2nd branch of philosophy- it is the science devoted to the discovery of the proper methods of acquiring and validating knowledge- and it is the foundation that every other field of science rests on- and therefore your lack or grasp of it- determines your success in any particular field.

Mike O,

Thanks so much for your truly impressive mastery of the copy-paste type of approach to distilling knowledge.

Your post made me realize how confused I am really, having no grasp of theoretical and experimental evidence.

I am very fortunate that you are willing, so enthousiasticaly, to further my education and show me the light.

 

[Mike O]

Grasshopper

Mike O,

Thanks so much for your truly impressive mastery of the copy-paste type of approach to distilling knowledge.

Your post made me realize how confused I am really, having no grasp of theoretical and experimental evidence.

I am very fortunate that you are willing, so enthousiasticaly, to further my education and show me the light.

You're welcome Grasshopper.

 

[mandrin]

Disappointed !

You're welcome Grasshopper.

The fun already over,
No more copy-pasting?
I am hungry for more!