Release action

[drewyallop]

Thank you for the clarification dbl and footwedge. I now understand Mandrin's conclusion that centripetal force is the cause of the release. I admit not reading the paper further after encountering the quoted passage (which I cannot find now). Apologies to Mandrin for the criticism.

Suggestion to Mandrin: Most scholarly papers begin with an abstract. I think your papers would benefit. Here is an example:

Previous research has emphasized the portfolio balance effects of Federal Reserve bond purchases, in which a reduced bond supply lowers term premia. In contrast, we find that such purchases have important signaling effects that lower expected future short- term interest rates. Our evidence comes from dynamic term structure models that decompose declines in yields following Fed announcements into changes in risk premia and expected short rates. To overcome problems in measuring term premia, we consider unbiased model estimation and restricted risk price estimation. We also characterize the estimation uncertainty regarding the relative importance of the signaling and portfolio balance channels.

 

[dbl]

Mandrin, two question from your web page's analysis:

1) From the conclusion area and the 2 pendulum work up, how does one generate the radial acceleration shown in Fig 31a?

2) The large force in Fig 29a is described later as often being "commonly" assumed to be "the centrifigual" force in other analyses, however it seems pointed inwards. Is that a reaction force, for example of the wrist against an outward directed force? Or, in essence, is this from the golfer pulling up against the club handle as it swings around him?

Reference
MYTH_CENTRIFUGAL_FINAL.NB

 

[mandrin]

Mandrin, two question from your web page's analysis:

1) From the conclusion area and the 2 pendulum work up, how does one generate the radial acceleration shown in Fig 31a?

2) The large force in Fig 29a is described later as often being "commonly" assumed to be "the centrifigual" force in other analyses, however it seems pointed inwards. Is that a reaction force, for example of the wrist against an outward directed force? Or, in essence, is this from the golfer pulling up against the club handle as it swings around him?

Reference
MYTH_CENTRIFUGAL_FINAL.NB

dbl,

What is confusing when confronted with rotation of a mass around a center is that, in a sense, there seems to be no motion, i.e., between the center and the mass. Yet there is a force inwards towards the center. In linear mechanics for a free particle this would result in a motion in the direction of the force. The centripetal force, however, is working hard to keep the lazy mass in the circular orbit by changing constantly its direction of motion. The mass wants to go straight but the centripetal force keeps pushing it for forever back into the circular orbit.

You just have to accept as a fact of nature that when any object rotates around a center a centripetal force is acting on it, just the same way you accept as natural that any object has weight due to gravity. Hence when you swing your arm around your shoulder socket you generate a centripetal force which acts inwards on all the parts of your arm. The centripetal force acting through the wrist joints on the butt end of the club is hence generated by the rotation of the arms around some center. The faster you rotate the arms the larger this centripetal force, as it is proportional to the angular velocity squared.

With regard to the second question the same arguments apply. The club through the impact zone primarily rotates around the wrists. Hence there is also a centripetal force associated with the rotation of the clubhead mass around the wrists. This force is generated at the wrist joints as shown in Fig29a.

The centripetal force associated with the arms is along the arms, inwards. Similarly the centripetal force associated with the club is along the shaft. There being no arm there is no torque, considered separately. But when we consider the mutual interaction of arms and club than we have an offset between centripetal force vector and center of mass and hence a torque can be generated.

 

[Virtuoso]

dbl,

The centripetal force associated with the arms is along the arms, inwards. Similarly the centripetal force associated with the club is along the shaft. There being no arm there is no torque, considered separately. But when we consider the mutual interaction of arms and club than we have an offset between centripetal force vector and center of mass and hence a torque can be generated.

Mandrin, I thought I had a good idea of cause and effect with the release, but clearly not, so tell me if I'm on track with the following:

Centrifugal force (or my definition of the clubhead's resistance to "making the forced left turn" is not the cause of the club "catching up."

We are applying a torque to the arms, and thus secondarily to the club, which is the application of the centripetal force.

There is indeed a reactive centrifugal force, and perhaps that accounts for the club "feeling heavy" in the impact zone, but, nevertheless, that is not causing the un-hinging or release, catching up.

The clubhead dramatically and violently catches up because i have intuitively learned how to slow the velocity of the more proximal parts of the system, and a large dose energy is distributed to the more distal parts--the most distal being the clubhead (the mass is small compared to the proximal parts, so inevitably, the velocity goes way up).

So, the clubhead is really flying, and trying to fly in a straight line, but I won't let go. By not letting go, well, that is why I feel a violent pulling sensation against my shoulder sockets. But again, that is the reaction of centrifugal force, not the cause of the clubhead speeding up to release.

 

[mandrin]

Mandrin, I thought I had a good idea of cause and effect with the release, but clearly not, so tell me if I'm on track with the following:

Centrifugal force (or my definition of the clubhead's resistance to "making the forced left turn" is not the cause of the club "catching up."

We are applying a torque to the arms, and thus secondarily to the club, which is the application of the centripetal force.

There is indeed a reactive centrifugal force, and perhaps that accounts for the club "feeling heavy" in the impact zone, but, nevertheless, that is not causing the un-hinging or release, catching up.

The clubhead dramatically and violently catches up because i have intuitively learned how to slow the velocity of the more proximal parts of the system, and a large dose energy is distributed to the more distal parts--the most distal being the clubhead (the mass is small compared to the proximal parts, so inevitably, the velocity goes way up).

So, the clubhead is really flying, and trying to fly in a straight line, but I won't let go. By not letting go, well, that is why I feel a violent pulling sensation against my shoulder sockets. But again, that is the reaction of centrifugal force, not the cause of the clubhead speeding up to release.

Virtuoso,

With regard to cause. First of all, cause is in the action of the contracting muscles acting on the various levers to create torques.

With regard to effect. Once motion is produced than one gets inertial forces such a centrifugal, centripetal and linear joint reaction forces.

Moreover with various masses interacting we have a multi body dynamics situation with non linear interactions between these various segments.

Regarding the golfer club as an ensemble, only real torques produced by contracting muscles can do work and hence generate net kinetic energy.

Inertial reaction forces/torques don't produce any net kinetic energy in this ensemble but can locally do work on sub segments and as a result redistribute kinetic energy in the system. This is the basic action of a kinetic chain.

The flow of some energy/momentum from arms to club during the down swing is something which happens always. However we can increase it some by torquing early in the down swing and letting go a bit subsequently.

 

[Virtuoso]

thanks Mandrin,

I'm still not comfortable in my understanding of joint reaction forces. I'm going to spend some more time studying your original post so I can come back with somewhat intelligent questions.

 

[Jon Hardesty]

How the heck does this thread only have 3 pages????

 

[omissions]

How the heck does this thread only have 3 pages????

because it's written in chinese for most of us?

 

[jenhaoyen]

because it's written in chinese for most of us?

cliff notes?

 

[rprevost]

I am no physicist!!! Now that I have made that clear, here is my comment and question. C: As I understand centripetal force, from the discussion here, it is the force, directed toward the golfer that keeps the clubhead from flying off in the line of the vector during the swing. As a layperson on these issues, I would ordinarily interpret that simply as my hand's gripping the club and not letting go; the centripetal force is applied to the club head through the hand's gripping the club;if I let go of the club, centripetal force disappears and the club goes down the fairway with the ball. Qs: How can I apply that fact to improve my golf swing? Given that fact, in what ways could one use that knowledge to one's advantage? Is the CP release one way to do so? By allowing a free wheeling action of the wrists, one allows the interaction of centripetal and vector forces to more efficiently interact to apply force to the ball?

 

[footwedge]

I am no physicist!!! Now that I have made that clear, here is my comment and question. C: As I understand centripetal force, from the discussion here, it is the force, directed toward the golfer that keeps the clubhead from flying off in the line of the vector during the swing. As a layperson on these issues, I would ordinarily interpret that simply as my hand's gripping the club and not letting go; the centripetal force is applied to the club head through the hand's gripping the club;if I let go of the club, centripetal force disappears and the club goes down the fairway with the ball. Qs: How can I apply that fact to improve my golf swing? Given that fact, in what ways could one use that knowledge to one's advantage? Is the CP release one way to do so? By allowing a free wheeling action of the wrists, one allows the interaction of centripetal and vector forces to more efficiently interact to apply force to the ball?

Rotation of the coupling point. Handpath is huge. JMO.

 

[mandrin]

I am no physicist!!! Now that I have made that clear, here is my comment and question. C: As I understand centripetal force, from the discussion here, it is the force, directed toward the golfer that keeps the clubhead from flying off in the line of the vector during the swing. As a layperson on these issues, I would ordinarily interpret that simply as my hand's gripping the club and not letting go; the centripetal force is applied to the club head through the hand's gripping the club;if I let go of the club, centripetal force disappears and the club goes down the fairway with the ball. Qs: How can I apply that fact to improve my golf swing? Given that fact, in what ways could one use that knowledge to one's advantage? Is the CP release one way to do so? By allowing a free wheeling action of the wrists, one allows the interaction of centripetal and vector forces to more efficiently interact to apply force to the ball?

rprevost,

For the average golfer science has perhaps little relevance. For the serious golfer when the utmost is sought likely a bit more. But expecting from science to get easy, clear instsructions is maybe not realistic. (Look here for a simple analysis, illustrating this last point). It is more like a sound foundation on which to build.

In the down swing all body parts move, mainly in a rotary fashion. The aim is to get maximum clubhead speed at impact. Most of the work done in getting all these body parts moving is wasted, in that only a small portion actually ends up in the form of clubhead speed. Those adhering to the concept of the kinetic chain action prone a sequential firing of body parts from the ground up to maximize this flow of kinetic energy from body to club.

The basic idea here is to consider two phases in the motion of various body parts in the down swing. First getting into motion and than subsequently slowing down a bit and hence giving up some energy down the line. Theoretically if all body parts would have temporarily no motion at impact suggests maximum kinetic energy being transferred to the club.

The most obvious part of the body for the golfer in this process are the arms. We all know the difference between muscling the arms throughout the downswing and the pleasant feeling of letting them free wheel though impact.

Freewheeling implies using not so muscle torque but instead the inertial forces, acting at the wrist joints. The wrist joint forces are responsible for the transfer of kinetic energy from arms to club. If we muscle the club through impact we might, if strong enough, largely prevent the arms from slowing down and hence hinder this energy transfer from arms to club.

Is one way to be preferred over the other ? Surely letting go gives a more efficient swing but golf is more than being efficient. It really invokes the debate of swinging vs hitting. An interesting question is if an efficient swing also relates to maximum possible clubhead speed. The human body/mind ensemble is a complex bit of machinery.

 

[rprevost]

Thanks, Mandrin!

 

[mandrin]

The simple double pendulum model for the golf swing shows that the hands slow down during the release phase of the swing and that it takes quite some effort to swing so as to not have the hands slow down.

Early stroboscopic swing sequences already showed this effect. Nowadays simply looking at the fascinating Minolta Swing Vision sequences of pro golfers it appears clearly that the hands slow down during the release phase.

What has recent golf science to say about this ?

Dr Nesbit (*1), measures a nearly constant hand speed prior to and through impact.






Dr. Grober's (*2) experimental findings indicate a decrease in the speed of the hands prior to impact.

“A comparative study of twenty-five golfers shows that clubhead speed is generated in the down swing as a two step process. The first phase starts at he top of the swing and involves impulsive acceleration of the hands and club. This is followed by a second phase, the releases, where the club is accelerated whilst the hands decelerate.”



P. J. Cheetam, G. A. Rose, R. N. Hinrichs, R J Neal, R. E. Mottram, P. D. Hurrion and P. F. Vint, (*3) report research findings which show a marked decrease in hand speed during release.





Dr. Nesbit's measurements regarding hand speed are apparently not quite in agreement with measurements by other golf scientists. In any case it shows that we should have a bit of restraint with golf scientific research. Some of these more recent research efforts are indeed based on intricate modeling, sophisticated measuring schemes and complex data processing procedures. For example, just simply the particular implementation of the low pas filtering of the raw data can have a significant influence on the meaning derived from this data.


1* - A THREE DIMENSIONAL KINEMATIC AND KINETIC STUDY OF THE GOLF SWING,
Journal of Sports Science and Medicine (2005) 4, 499-519,
Steven M. Nesbit.

2* - Measuring Tempo, Rhythm, Timing, and the Torques that Generate Power in the Golf Swing (2010)
arXiv:1001,1137v1
Robert D. Grober

3* - Comparison of Kinematic Parameters between Amateur and Professional Golfers,
SCIENCE AND GOLF V, 2008,
P. J. Cheetham, G. A. Rose, R. N. Hinrichs, R. J. Neal, R. E. Mottram, P. D. Hurrion, P. F. Vint.

 

[Michael Jacobs]

The simple double pendulum model for the golf swing shows that the hands slow down during the release phase of the swing and that it takes quite some effort to swing so as to not have the hands slow down.

Early stroboscopic swing sequences already showed this effect. Nowadays simply looking at the fascinating Minolta Swing Vision sequences of pro golfers it appears clearly that the hands slow down during the release phase.

What has recent golf science to say about this ?

Dr Nesbit (*1), measures a nearly constant hand speed prior to and through impact.






Dr. Grober's (*2) experimental findings indicate a decrease in the speed of the hands prior to impact.

“A comparative study of twenty-five golfers shows that clubhead speed is generated in the down swing as a two step process. The first phase starts at he top of the swing and involves impulsive acceleration of the hands and club. This is followed by a second phase, the releases, where the club is accelerated whilst the hands decelerate.”



P. J. Cheetam, G. A. Rose, R. N. Hinrichs, R J Neal, R. E. Mottram, P. D. Hurrion and P. F. Vint, (*3) report research findings which show a marked decrease in hand speed during release.





Dr. Nesbit's measurements regarding hand speed are apparently not quite in agreement with measurements by other golf scientists. In any case it shows that we should have a bit of restraint with golf scientific research. Some of these more recent research efforts are indeed based on intricate modeling, sophisticated measuring schemes and complex data processing procedures. For example, just simply the particular implementation of the low pas filtering of the raw data can have a significant influence on the meaning derived from this data.


1* - A THREE DIMENSIONAL KINEMATIC AND KINETIC STUDY OF THE GOLF SWING,
Journal of Sports Science and Medicine (2005) 4, 499-519,
Steven M. Nesbit.

2* - Measuring Tempo, Rhythm, Timing, and the Torques that Generate Power in the Golf Swing (2010)
arXiv:1001,1137v1
Robert D. Grober

3* - Comparison of Kinematic Parameters between Amateur and Professional Golfers,
SCIENCE AND GOLF V, 2008,
P. J. Cheetham, G. A. Rose, R. N. Hinrichs, R. J. Neal, R. E. Mottram, P. D. Hurrion, P. F. Vint.

Mandrin,

Question and comments for you:

1. Your thoughts on The simple double pendulum model not accounting for the non circular path of the hands ?

2. The Phil Cheetham graph highlight you have is of the arm?

3. Your thoughts on this quote from Dr Nesbit that is shortly after the graph you posted:
"It is interesting that while the grip velocity remains relatively constant or slightly decreases near impact, the grip acceleration curves increase slightly. This indicates a shortening of the hub radius near impact and was seen in all 84 subjects"

 

[natep]

I find this hand-speed stuff confusing as well. I was once directed to this newsletter by Dr. Rob Neal:

http://golfbiodynamics.com/downloads/newsletters/GBD_Newsletter_4.pdf

in which he explains how he has upgraded his model by changing how the hand speed was measured. He shows graphs of his old model that show the hands slowing down pre-impact, and in the new model the hands accelerate into impact. I think he changed the way he measured from linear speed to angular speed? I dont fully understand the differences and the implications.

 

[Brian Manzella]

Nesbit:

"It is interesting that while the grip velocity remains relatively constant or slightly decreases near impact, the grip acceleration curves increase slightly. This indicates a shortening of the hub radius near impact and was seen in all 84 subjects"

 

[mandrin]

Mandrin,

Question and comments for you:

1. Your thoughts on The simple double pendulum model not accounting for the non circular path of the hands ?

2. The Phil Cheetham graph highlight you have is of the arm?

3. Your thoughts on this quote from Dr Nesbit that is shortly after the graph you posted:
"It is interesting that while the grip velocity remains relatively constant or slightly decreases near impact, the grip acceleration curves increase slightly. This indicates a shortening of the hub radius near impact and was seen in all 84 subjects"

Michael,

ad 1.
The double pendulum model does not account for a host of things, yet for a fairly long time many golf scientists used it as their mathematical model for studying the golf swing.

It is indeed surprising that such a very simple model could have been still so useful towards a more scientific understanding of the golf swing.

Dr. Jorgensen, in The Physics of Golf, already started to use a non circular hand path by including the lateral motion of the golfer in his double pendulum model,.

Miura also deviated from the circular hand path for double pendulum models, by including some vertical motion into the double pendulum model.

More recently Dr Nesbit and McGinnis (1*) have looked more in detail at hand path, but again this being done in a 2D planar environment.

The essence of the golf swing is made up of arms and club and to a first order approximation constitutes a typical 2D phenomenon.


ad2.
I highlighted the arm curve. Nevertheless the curves were already clearly marked re to which body part they refer to.


ad3.
Intuitively one expects a shortening of the radius to actually result in an increase of the linear speed. But we have to consider the complex interaction of club and arms. The clubhead accelerates also and hence there is a decelerating torque on the arms. Needs some more analysis.


1* Kinematic analyses of the golf swing hub path and its role in golfer/club kinetic transfers,
Journal of Sports Science and Medicine (2009) 8, 235-246,
Steven M. Nesbit and Ryan McGinnis

 

[Michael Finney]

Mandrin

Thanks so much for the release analysis......could one say that the centripetal force acting up the arm with relation to the centripetal force acting up the shaft creates the arm upon which the golfer now can apply a torque?

Or is it just the simple fact that the centers of mass are offset that gives the golfer the green light to
apply a torque?

 

[mandrin]

Mandrin

Thanks so much for the release analysis......could one say that the centripetal force acting up the arm with relation to the centripetal force acting up the shaft creates the arm upon which the golfer now can apply a torque?

Or is it just the simple fact that the centers of mass are offset that gives the golfer the green light to
apply a torque?

Michael,

The whole release analysis is centered on the torque exerted on the shaft as it determines the release action of the club through impact, i.e., catching up and quickly over taking the arms through impact. This is never really explained and usually it is disposed off erroneously as being caused by the centrifugal force acting on the club.

If one considers the total force acting on the wrist joint than the picture is obscured by the dominant centripetal force acting along the club shaft but not contributing to any release torque. Hence to be able to analyze the release action one has to dissect this total joint force into its various components, associated with the angular and radial (centripetal) acceleration of arm and club, in addition to wrist torque and gravity.

In general to obtain angular and /or radial acceleration for a body requires a torque and hence a force having some moment arm. The magnitude of a torque depends on the magnitude of the force, the length of the lever arm, and the angle between the force vector and the lever arm. Fig1 shows the club, shown as a free body diagram. Since we have taken the club to have a massless shaft and the clubhead to be a point mass, it follows that the moment arm relative to the point of application is simply the distance L between wrist joint and clubhead.

Looking at figs 28a to 33a and/or figs 35a to 42a, one can get a quick global view by looking at the amplitude of the force vectors acting at the joint and the angle they are making with the club shaft. The resulting corresponding torques are shown in figs 28b to 33b and figs 35b to 42b. If you look respectively at fig 29a and fig 36a one notices that there is no angle between the club centripetal force and the club shaft and hence there is also no release torque associated with this very large centripetal force component throughout the release.

However the force associated with the radial (centripetal) acceleration of the arm, having an angle with the club shaft, can exert a torque on the shaft. It is this particular torque associated with the radial (centripetal) acceleration of the rotating arm which is really the dominant factor in the intriguing release action of the club through impact. See Figs 31a and 31b and also Figs 38a and 38b.