Ground reaction forces / angular momentum

[mandrin]

On occasion one will find instruction or forum discussions mentioning that ground reaction forces should to be used efficiently, or perhaps even suggesting to be a possible source for additional power input to the golf swing. Let's be clear about this... ground reaction forces are indeed just only...reaction forces. The primary and only source and cause for action in a golf swing is the golfer himself.

Also contrary to a persistent long standing believe, angular momentum is not conserved in a golf swing. Hence better forget about COAM often used with regard to a golf swing. Perhaps the earliest reference to and use of COAM to explain a golf swing is to be found in “Four Magic Moves to Winning Golf 'by Joe Dante.

I had a closer look at the interplay of angular momentum and ground reaction torque. Angular momentum is not conserved in a golf swing. Also the ground reaction torque is primarily caused by the internal most proximal torque, generated by the golfer. The distal wrist torque, for instance, generates a negligible ground reaction torque.

 

[jpvegas1]

Missed your posts Mandrin, glad you've posted again.

What effect, if any, has the switch from metal to plastic spikes had on the golfer's ability to generate internal forces leading to increasing the ground reaction forces? (Do the plastic spike lead to a decreased connection between the golfer and the ground?)

 

[Damon Lucas]

Mandrin,

Is the most proximal 'internal torque' activated in the left hip socket or in the left ankle?

Why would the same golfer be able to generate more torque with golf shoes and the ground versus standing on a block of ice in flat shoes?

Thank you,
Damon

 

[Michael Finney]

if the golfer didn't have the "previously generated available angular momentum" of the lower body, then there would be nothing to redistribute - correct?

the fact that the momentum is merely being "redistributed" later in the swing shouldn't dissipate its (the momentum gained from the ground reaction forces) importance, correct?

 

[PChandler]

Mandrin

My copy of The Four Magic Moves to Winning Golf is written by Joe Dante with Len Elliott.

PChandler

 

[Dariusz J.]

Mandrin,

Is the most proximal 'internal torque' activated in the left hip socket or in the left ankle?

Why would the same golfer be able to generate more torque with golf shoes and the ground versus standing on a block of ice in flat shoes?

Thank you,
Damon

The bigger the friction the bigger the torque in the joints can be. Sometimes body mass or human effort is not enough to create a necessary ground force to benefit from later on. Human joints and their reaction to physics deserve much more attention (best from the ground up) that we can imagine.

Cheers

 

[mandrin]

Missed your posts Mandrin, glad you've posted again.

What effect, if any, has the switch from metal to plastic spikes had on the golfer's ability to generate internal forces leading to increasing the ground reaction forces? (Do the plastic spike lead to a decreased connection between the golfer and the ground?)

jpvegas,

I really don't think that spikes are all that important under normal conditions. Also I would not be surprised if plastic spikes are producing very much the same friction, perhaps even more than when using metal spikes. But I am just making an educated guess.

The twisting force developed by the golfer relative to the earth is generated by noncollinear horizontal forces acting in opposite directions. These forces are matched by equal and opposing friction forces between shoes and ground. As long as these static friction forces are large enough no problem. However going beyond a certain maximum, determined by the static friction coefficient, slipping occurs and one better throttles down a bit.

 

[mandrin]

Mandrin,

Is the most proximal 'internal torque' activated in the left hip socket or in the left ankle?

Why would the same golfer be able to generate more torque with golf shoes and the ground versus standing on a block of ice in flat shoes?

Thank you,
Damon

Damon,

I am not a biomechanical expert. There are joints at the ankles, knees and hips but personally would pick both ankles as the source for the most significant proximal torques.

The muscles are the same regardless of the type of support, either ground or frictionless surface. Therefore the potential to develop a torque is he same. So what is different?

Imagine the earth shrinking to the size and weight of a soccer ball. Instead of swinging a golf club you will be manipulating a soccer ball. With the earth its normal size and weight it is the other way around. Also think of two very different masses with a compressed spring between. When letting go only the small weight will move substantially, the large one remaining virtually motionless.

A similar argument applies when considering the coefficient of friction of the surface underneath the golfer. For a supporting mass to be able to form an adequate resistance for a golf swing it not only needs to be very large but it also requires to furnish a reasonable friction force. The earth surface on a golf course does but a slippery ice surface does not.

 

[mandrin]

if the golfer didn't have the "previously generated available angular momentum" of the lower body, then there would be nothing to redistribute - correct?

the fact that the momentum is merely being "redistributed" later in the swing shouldn't dissipate its (the momentum gained from the ground reaction forces) importance, correct?

Michael,

Yes, to the first question. Yes and no to the second question. There is not merely redistribution later on as it would imply total absence of any torque. Hence angular momentum will normally still be generated.

At the beginning of the golf swing there is no angular momentum whatsoever. During the down swing there is continuously momentum being generated.

However in a swing with free wheeling through impact there will be in the second half of the down swing, a certain significant amount of redistribution of angular momentum towards the clubhead.

But in a swing where one strives for maintaining significant acceleration/torquing during impact there will way less redistribution as it is only by letting proximal elements naturally slow down that redistribution can take place.

Nevertheless, one can consider a golf swing to have two phases. First only a generating phase followed by second phase with also some redistribution - its importance depending on the individual golf swing.

One can use the two-phase image of filling first, for some time, a container with water and than, whilst continuing to fill, to also distribute it to thirsty onlooking golfers.

 

[Jon Hardesty]

Mandrin,

Is it the uncocking of the club on the downswing what slows the hands down? Thus creating a two way street in that as the hands slow down the club speeds up by uncocking from the wrists and thusly slowing the hands down?

Also, do you think that someone with a tremendous amount of lag well into the downswing would be working against themselves by not allowing the club to uncock from the wrists thus slowing the hands down enough to allow the club to speed up?

It's good to see you back!

 

[Michael Finney]

Michael,

Yes, to the first question. Yes and no to the second question. There is not merely redistribution later on as it would imply total absence of any torque. Hence angular momentum will normally still be generated.

At the beginning of the golf swing there is no angular momentum whatsoever. During the down swing there is continuously momentum being generated.

However in a swing with free wheeling through impact there will be in the second half of the down swing, a certain significant amount of redistribution of angular momentum towards the clubhead.

But in a swing where one strives for maintaining significant acceleration/torquing during impact there will way less redistribution as it is only by letting proximal elements naturally slow down that redistribution can take place.

Nevertheless, one can consider a golf swing to have two phases. First only a generating phase followed by second phase with also some redistribution - its importance depending on the individual golf swing.

One can use the two-phase image of filling first, for some time, a container with water and than, whilst continuing to fill, to also distribute it to thirsty onlooking golfers.

So could you say that in the first phase of the swing angular momentum is generated by the external reaction ground forces and during the second phase angular momentum is being conserved? Or is that way too simplified for what is really going on?

Thanks for the responses.

 

[mandrin]

Mandrin,

Is it the uncocking of the club on the downswing what slows the hands down? Thus creating a two way street in that as the hands slow down the club speeds up by uncocking from the wrists and thusly slowing the hands down?

Also, do you think that someone with a tremendous amount of lag well into the downswing would be working against themselves by not allowing the club to uncock from the wrists thus slowing the hands down enough to allow the club to speed up?

It's good to see you back!

Jon, I think we are bifurcating onto another avenue and moving away from angular momentum/ground reaction forces.

The mathematical expressions for the torques, even for a simple double pendulum model, consists of rather complex relations. We are all looking for simple answers but dynamic interaction of linked segments is a complex business.

The golf club unfolds not due to the centrifugal force exerted on the club but primarily due to the linear force exerted through the wrist joint on the club by the arms. This force has two distinct sources – angular acceleration of arms and angular speed of arms and it generates corresponding torques acting on the golf club.

Once the club is rapidly releasing, due to a large torque acting on it, there is also (Newton's third law} and equal and opposing torque exerted back onto the arms. Hence the more rapidly the club releases the more there is an equivalent increase in the 'braking' torque on the arms.

Hence the faster you swing the more there will be also a larger force trying to decelerate the hands. It will happen automatically and is a good example of a self regulating mechanism without which it would be very difficult to hit a golf ball consistently with reasonable accuracy.

If I remember things I did quite a while ago, trying to maintain the angle, perhaps counter intuitive, does even result in slightly increased club head speed. And also, probably more important, assures that the hands arrive at impact before the clubhead.

Retarding release results in a smaller moment of inertia during the downswing for a longer time and hence a bit more angular velocity for the same torque. The 'release' torque builds up very fast in a down swing and retarding release will lead to a more explosive release action and hence still resulting in correct impact alignments.

Torque will increase clubhead speed but also redistribution due to deceleration, complex little game.

 

[Jon Hardesty]

Thanks Mandrin for the response. I probably should have started a seperate thread on this topic. However, very interesting stuff! Thanks.

 

[mandrin]

So could you say that in the first phase of the swing angular momentum is generated by the external reaction ground forces and during the second phase angular momentum is being conserved? Or is that way too simplified for what is really going on?

Thanks for the responses.

Michael,

First of all we have to be clear about the use of the verb... 'to conserve'. The every day use is more along the lines of to protect from loss or avoiding waste. This is for instance true when filling a container with water making sure there are no holes from which water can escape whilst filling and causing waste.

It is important to make this distinction as I feel that many believe that if angular momentum is not wasted it is hence, as a consequence, conserved and thus COAM applies. Not true. Conservation of angular momentum as used by scientists is one of the most fundamental laws in physics and 'conservation' is used in the precise sense of being constant, not varying.

This indeed occurs for instance when a figure skater making multiple rotations during a jump or even a spin, truly conserving angular momentum. Same for a trampoline pirouette or board driver's jump. But not true in a golf swing.

For COAM to be applicable there has to be no net external torque acting on the system. This would be the case if the golfer would be swinging his club whilst standing on a surface with no friction. But than one can't swing a club without falling on one's rear end.

Therefore without going into any complicated detail – just the simple fact that plenty of friction is required to maintain balance indicates that during the golf swing continuously an external torque is required and acting on the golfer/club ensemble.

A golfer's swing is a very individual thing. Some let the club coasting through impact some exert a strenuous effort through impact. This has a large influence on how angular momentum is generated and distributed during a golf swing.

However simpifying one can still say that there two phases. First primarily generation of angular momentum followed by a phase where there is also distribution of angular momentum. But during the golf swing the total angular momentum is not constant and continuously changing.

 

[Steve Khatib]

Therefore without going into any complicated detail – just the simple fact that plenty of friction is required to maintain balance indicates that during the golf swing continuously an external torque is required and acting on the golfer/club ensemble.


Great stuff Mandrin, many thanks. Approxiamately what ratio of external torque is required to maintain balance?

Best Regards,
Steve

 

[Brian Manzella]

Must read for Method Teachers, and Swing Theorists....

Thanks for this golden one (below). Dr. Zick agrees.

The golf club unfolds not due to the centrifugal force exerted on the club but primarily due to the linear force exerted through the wrist joint on the club by the arms.

The golf club unfolds not due to the centrifugal force exerted on the club but primarily due to the linear force exerted through the wrist joint on the club by the arms.

The golf club unfolds not due to the centrifugal force exerted on the club but primarily due to the linear force exerted through the wrist joint on the club by the arms.

The golf club unfolds not due to the centrifugal force exerted on the club but primarily due to the linear force exerted through the wrist joint on the club by the arms.

The golf club unfolds not due to the centrifugal force exerted on the club but primarily due to the linear force exerted through the wrist joint on the club by the arms.

 

[ggsjpc]

What a gem right here

Jon, I think we are bifurcating onto another avenue and moving away from angular momentum/ground reaction forces.

The mathematical expressions for the torques, even for a simple double pendulum model, consists of rather complex relations. We are all looking for simple answers but dynamic interaction of linked segments is a complex business.

The golf club unfolds not due to the centrifugal force exerted on the club but primarily due to the linear force exerted through the wrist joint on the club by the arms. This force has two distinct sources – angular acceleration of arms and angular speed of arms and it generates corresponding torques acting on the golf club.

Once the club is rapidly releasing, due to a large torque acting on it, there is also (Newton's third law} and equal and opposing torque exerted back onto the arms. Hence the more rapidly the club releases the more there is an equivalent increase in the 'braking' torque on the arms.

Hence the faster you swing the more there will be also a larger force trying to decelerate the hands. It will happen automatically and is a good example of a self regulating mechanism without which it would be very difficult to hit a golf ball consistently with reasonable accuracy.

If I remember things I did quite a while ago, trying to maintain the angle, perhaps counter intuitive, does even result in slightly increased club head speed. And also, probably more important, assures that the hands arrive at impact before the clubhead.

Retarding release results in a smaller moment of inertia during the downswing for a longer time and hence a bit more angular velocity for the same torque. The 'release' torque builds up very fast in a down swing and retarding release will lead to a more explosive release action and hence still resulting in correct impact alignments.

Torque will increase clubhead speed but also redistribution due to deceleration, complex little game.

Note to self: Remember, study and internalize.

 

[mandrin]

Therefore without going into any complicated detail – just the simple fact that plenty of friction is required to maintain balance indicates that during the golf swing continuously an external torque is required and acting on the golfer/club ensemble.


Great stuff Mandrin, many thanks. Approxiamately what ratio of external torque is required to maintain balance?

Best Regards,
Steve

Steve,

I don't know quite how to answer your question. A bit of googling gave some idea of the torque associated with each foot during the swing.

Journal of Sports Science and Medicine (2008) 7, 408-414.

Paul Worsfold, Neal A. Smith and Rosemary J. Dyson

University of Chichester, Chichester, West Sussex, UK

 

[mandrin]

Missed your posts Mandrin, glad you've posted again.

What effect, if any, has the switch from metal to plastic spikes had on the golfer's ability to generate internal forces leading to increasing the ground reaction forces? (Do the plastic spike lead to a decreased connection between the golfer and the ground?)

jpvegas,

I guessed right.

"There was no significant difference between the metal and alternative spike shoes for any torque measure (p > 0.05), ..................."

Journal of Sports Science and Medicine (2008) 7, 408-414

 

[tobell]

Pivot braking

Mandrin,

Great stuff as usual--thanks! Your point regarding redistributing forces is a great way to regard the swing IMO. I believe I recall a post from some time ago that mentioned the potential of accelerating the club by braking the pivot...essentially redistributing proximal forces to the distal attachment by intentional braking or retarding the pivot as the club approached impact.

Baseball season fast approaches here in the US. I had my son experiment with this idea in the batting cages. Instead of pivoting faster in response to a faster pitch he intentionally stalled his pivot once he initiated the swing...the bat flew inline much quicker and he was able to non nonchalantly handle the fastest pitching the batting cages could muster. Amateur baseball players often respond to faster pitching by pivoting faster..this results in a dragging attachment...they need to redistribute and listen to Mandrin.