CP/CF release

[SteveT]

The 3rd law demands that there be another force equal in magnitude to that force, the vector pointing in a direction opposite to the centripetal force. This is non-negotiable.

This is what I'm asking mandrin to fully define in the context of my questions. So far nothing.

 

[leon]

drewyallop... you're an engineer, I believe, so I ask you, is Cf a force or just a feeling that is not real? We know that Cp is an 'applied' force, but what about Cf? It's not enough to label Cf a 'reactive' force without showing it in a FBD of the system.

I'm waiting for mandrin to respond to my last comments, and hopefully he will finally clarify everything... I hope.

Steve, can you clarify what fbd exactly you are expecting? Usually you would isolate a single body, i.e. the mass, and Mandarin already did this in his original post. You are asking for the 'system', but there are only two bodies, the mass and spring, so this would just show a single force (the cp force, if you want to call it that) at the inner end of the spring. If you want to see the corresponding 'cf' force you'd need a fbd of the central support to which the spring is attached. And of course you could move ever outwards, to whatever the support is attached, to the ground, the earth itself, etc.
If you apply a force to anything, it equally applies one back to you. It might not be obvious, and you might not 'feel' it, but its there. It has to be. Newton says so. Something about apples apparently

 

[SteveT]

leon.... I'm still waiting for mandrin's response to my last set of questions, and I prefer to wait for him to clarify his diagrams. Later....

 

[mandrin]

leon.... I'm still waiting for mandrin's response to my last set of questions, and I prefer to wait for him to clarify his diagrams. Later....

SteveT,

All that time you are waiting fore something you can't really name or specify. I suspect it is my artwork you like and you want simply more of it. Hence I have prepared more than you asked for in appreciation for your silent admiration.

 

[SteveT]

SteveT,

All that time you are waiting fore something you can't really name or specify. I suspect it is my artwork you like and you want simply more of it. Hence I have prepared more than you asked for in appreciation for your silent admiration.

Thank you for your response, and I am puzzled that you would say I posted "something you(I) can't really name or specify." I posted my questions in message #44, namely:

Here's Fig.2 again:

In the second position, you show a blue centrifugal force vector acting on the mass after the spring is fully sprung. How would you draw the centrifugal force vector from the original position to it's final spring position, is the centrifugal force constant or variable as the spring stretches?

In the third position, you show a red centripetal force acting on the mass, but where is the centrifugal force vector? If you say these forces are concomitant, I would like to see how you place them together in your figures.

What I'm asking of you is to show both the centrifugal and centripetal forces acting simultaneously and on which masses they act... in a simple and complete free body diagram of the entire rotating system.

As for "no circular motion", that's obvious... but there is curvilinear motion occurring during 'transition'. Where are the centrifugal and centripetal forces acting on the system during transition.. their direction and relative magnitude?

I don't want to belabor the point, and I hope my questions merit your attention. Thank you in advance for accommodating my inquiries and correcting me where necessary.

What is it that you found inadequate in my above posting? Regardless, your interesting analysis helps me understand your concept of Cp and Cf, and how you attempt to verify it.

I'm particularly interested in Figs. 4, a/b/c/d. I have never seen such an array of forces acting on a rotating mass, and I would like you to explain how somebody might sense these forces while twirling a mass and while transitioning from one radius to the other radius, since they are essentially all 'reaction' forces.

The golfswing is slightly elliptical so there is a transition of swing radii.

How would composite Fig. 4(d) affect the golf club and how might the golfer cope with these forces... if they are applicable to the golfswing?

Hoping to hear from you, soon.....

 

[grahler]

You know Steve its interesting to me-as a player I only have a sense of feel and intent. As an analyst I try to comprehend physics etc in order to improve my play and keep my intent correct in terms of science-it's not easy.
I find that analysis can result in truth but that truth is only useful if it can be related to a feel so that the player can execute better.
Brian has a tough job and after speaking with him I gained respect because turning knowledge into feel and intent for a hundred different types of people can't be easy and he seems to be one of the few individuals who have a high batting average in terms of communicating in a way that folks can comprehend.
Its easy to chase knowledge of physics/science etc but without an ability to translate knowledge and truth into feel its useless. TY to Brian for bridging the gap-I have gained power in my swing from reading this site.

 

[SteveT]

grahler.... I agree and appreciate the problems for golfers with homemade 'feel' golfswings trying to adapt/evolve into structured 'scientific' golfswings.

I did it for myself, to the best of my abilities, but I doubt the average golfer seeking instant fixes would make the long term commitment to altering their mind and body... brains and neuromuscular system... because it requires athletic effort and time time time.

I had to make that effort because I was not hard-wired for the golfswing and had to remold a set and mature body if I wanted to play decent golf. It took many years of practice, and much of that practice was misguided too. It was an experiment that I concluded about 10 years ago. Those who are accomplished golfers will be able to adapt quickly, but novice golfers have a long way to go before they can expect selective help from science... because most are not athletically fit.

Brian et al will also encounter that resistance to change, with golfers expecting a magical scientific golfswing fix by just trying it. "If it's so good why doesn't it work for me?" will be the attitude amongst the duffer masses. Golf is more difficult than basketball and tennis, my other sport conquests..!

'Feel' must be replaced with proper 'action'... because feel comes after action. Many think feel can be anticipated and it will happen... nope. Hunting for 'feel' is just not athletic... it's the wrong path.

 

[mandrin]

Mandrin,

My background and career has been in science, and I very much appreciate the informative posts you always provide.

My current effort is to better understand the summation of the CP/CF forces of the major rotary actions of a typical golf swing, ie. the pelvis/lower body, the torso/shoulder complexes, the arms and of course the club. I anticipate the 3D summation of these collective forces having a significant impact on dynamic balance, and showing up in the vertical and horizontal measurements of ground reaction forces. Comments please, and can your model(s) depict these vectors as a function of time during the golf swing ??

art,

Your questions are a fair challenge even for the likes of Dr Nesbit, who is one of the leading golf scientists. I am definitely not into the same league, I usually keep things to 2d. But nevertheless even in 2d there is some room for interesting observations. Particularly since the arms and club can be taken as moving approximately in one plane. On occasion I have modelled a bit in three dimensions only to realize that it is not just meant to be done a bit here and there in one's spare time. Scientists seem to agree that beyond three degrees of freedom a math model of a golfer is neither useful or practical. Too many assumptions have to be made. Nowadays one has powerful commercial software which allows the golf scientist to use sophisticated 3D modeling when combined with measurements on real golfers, using a mix of forward and inverse dynamics. I have done however an elementary analysis of the relation between angular momentum, torques and ground reaction forces which you might find interesting.

Analysis of conservation of angular momentum using model including ground reaction force

 

[drewyallop]

Nice piece of work Mandrin. Is it fair to say that the "ground reaction force" is the same as "frictional force"?

 

[mandrin]

Nice piece of work Mandrin. Is it fair to say that the "ground reaction force" is the same as "frictional force"?

drewyallop,

Partly true. The friction forces are the horizontal components of the ground reaction force. There is first of all the weight of the golfer being pulled toward the center of the earth. The earth surface resists with a vertical reaction force equal to the static or dynamic weight of the golfer. The ground reaction force is the vector sum of the vertical and horizontal reaction forces.

The horizontal friction forces are all important. Golf shoes are designed to increase the friction force. On a frictionless surface no horizontal friction forces. The horizontal friction forces allow the golfer to develop torques especially having the two feet a certain distance apart. Gravity is responsible for the friction forces between shoes and ground. Subsequently the horizontal friction forces allow the golfer, through his feet, to develop a torque relative to the earth.



The ground reaction forces are measured with force plates. There are a multitude of measurements required as the ground reaction force has three orthogonal force components and three orthogonal torque components. Force platforms are used extensively in biomechanics, e.g., for gait studies. Dr Nesbit included them as part of his 3D model of a golfer.

 

[art]

art,

Your questions are a fair challenge even for the likes of Dr Nesbit, who is one of the leading golf scientists. I am definitely not into the same league, I usually keep things to 2d. But nevertheless even in 2d there is some room for interesting observations. Particularly since the arms and club can be taken as moving approximately in one plane. On occasion I have modelled a bit in three dimensions only to realize that it is not just meant to be done a bit here and there in one's spare time. Scientists seem to agree that beyond three degrees of freedom a math model of a golfer is neither useful or practical. Too many assumptions have to be made. Nowadays one has powerful commercial software which allows the golf scientist to use sophisticated 3D modeling when combined with measurements on real golfers, using a mix of forward and inverse dynamics. I have done however an elementary analysis of the relation between angular momentum, torques and ground reaction forces which you might find interesting.

Analysis of conservation of angular momentum using model including ground reaction force

Dear mandrin,

My personal trip on this scientific journey seeking 'golf truth' began with the discovery of several of Dr. Steve Nesbits papers published in the Journal of Sports Science and Medicine, and available free on the internet. After reading and studying "Work and Power Analysis of the Golf Swing" I realized/imagined how analogous this body, golf club, ball, and earth 'system' was to the complex flight dynamics and characteristics of airplane, rocket, satellite, and orbiting space systems that formed the basis of my 47 year 'dream' career.

However, in addition to the hundreds of other research papers I studied, there was another main boost to my scientific enthusiasm, and that had to do with some very informative mini-analyses I was led to from this Manzella site, and composed by a scientist I have grown to greatly respect by the pseudo name of, yes, mandrin.

I now have a folder of many of your articles, and have used characteristics/results of you detailed torque, velocity and acceleration findings and insights, to 'anchor' the hypotheses that in the down swing, dynamic imbalances and timing MAY be the cause of all unacceptable golf shots.

Welcome back, and thanks, for your interest and efforts, and please keep feeding the 'angelfire site' with the high quality insights and answers to the questions we keep throwing at you.

Sincerely and very appreciatively,
art

 

[drewyallop]

Experiment 3a - Torque between m3 and m4. No connection between m1 and ground.

​

​

Experiment 4a - Torque between m3 and m4.

The trend definitely continues as is there is now no noticeable increase in total angular momentumdue to the torque between disks 3 and 4. In other words a golfer with spikes on grass and a golfer barefooted on a very slippery surface, when torquing his wrist, produces virtualy the same effect on the system.
Hence in our last experiments the internal torque applied betweenm m3 and m4 does not increase the angular momentum of the system, its contribution is negligible.

Mandrin,

Am I reading the rightmost graph correctly that there is no increase in angular momentum of the system? If so, what happened to the external ground reaction force that was input initially?

Also where is the reference point for the calculation of the angular momentum of the system (I am interested - I like to fool with angular momentums)?

 

[drewyallop]

drewyallop,

Partly true. The friction forces are the horizontal components of the ground reaction force. There is first of all the weight of the golfer being pulled toward the center of the earth. The earth surface resists with a vertical reaction force equal to the static or dynamic weight of the golfer. The ground reaction force is the vector sum of the vertical and horizontal reaction forces.

The horizontal friction forces are all important. Golf shoes are designed to increase the friction force. On a frictionless surface no horizontal friction forces. The horizontal friction forces allow the golfer to develop torques especially having the two feet a certain distance apart. Gravity is responsible for the friction forces between shoes and ground. Subsequently the horizontal friction forces allow the golfer, through his feet, to develop a torque relative to the earth.



The ground reaction forces are measured with force plates. There are a multitude of measurements required as the ground reaction force has three orthogonal force components and three orthogonal torque components. Force platforms are used extensively in biomechanics, e.g., for gait studies. Dr Nesbit included them as part of his 3D model of a golfer.

Thanks Mandrin. Shouldn't there be a vector for g​?

 

[SteveT]

Thanks Mandrin. Shouldn't there be a vector for g​?

There is a vector for 'g' in W = m•g... but it's located at the body Center of Mass. Weight 'W' is resolved at the feet as GRFs... dynamic thrust too.

There is another significant ground reaction and it's shear torque which you can easily 'feeel'....

 

[mandrin]

Thanks Mandrin. Shouldn't there be a vector for g​?

drewyallop,

Don't forget we are dealing with ground reaction forces. The attraction between earth and golfer, is an action force. This force, commonly referred to as weight, is equal to m g.

This downward gravity action force, pressing the feet against the earth, results in the vertical ground reaction force Fy, and is also responsible for the friction forces and hence allows torque and thus a golf swing. Without gravity no friction and no golf.

Hence I could show indeed the downward gravity force vector but it is not logically required when dealing only with ground reaction forces.

 

[SteveT]

Hey, mandrin... show drewy a complete FBD including "W" at the navel and how it's resolved statically (50-50 and even 60-40 weight distributions) through the legs into the ground... he deserves it. If you want to get fancy, you can even throw in some ground reaction thrust and torque at different phases of the golfswing. You can do it ....

 

[mandrin]

Experiment 3a - Torque between m3 and m4. No connection between m1 and ground.

​

​

Experiment 4a - Torque between m3 and m4.

The trend definitely continues as is there is now no noticeable increase in total angular momentumdue to the torque between disks 3 and 4. In other words a golfer with spikes on grass and a golfer barefooted on a very slippery surface, when torquing his wrist, produces virtualy the same effect on the system.
Hence in our last experiments the internal torque applied betweenm m3 and m4 does not increase the angular momentum of the system, its contribution is negligible.

Mandrin,

Am I reading the rightmost graph correctly that there is no increase in angular momentum of the system? If so, what happened to the external ground reaction force that was input initially?

Also where is the reference point for the calculation of the angular momentum of the system (I am interested - I like to fool with angular momentums)?

drewyallop,

Every action torque is accompanied by a reaction torque, Newton's third law. The wrist torque exerts an action torque on the club shaft but there is also an equal and opposite torque acting on the arms. Similarly for arms and shoulders, shoulders and midsection, midsection and hips, hips and legs , legs and earth.

One thing must be clearly understood – the internal torques generated by the golfer have eventually a reactive counterpart, small or large, relative to the earth. This reaction torque acts now as an external torque to the golfer/club ensemble and generates the angular momentum. Its is kind of strange but so be it.

The analysis shows that the proximal torques generate substantial angular momentum whereas torques more distal such as wrist torque, do less or practically not at all. They however do redistribute existing angular momentum, e.g., flowing from arms to club during the release.

Now more specifically your questions.

Am I reading the rightmost graph correctly that there is no increase in angular momentum of the system? If so, what happened to the external ground reaction force that was input initially?

For the torque between mass m3 and m4 indeed there is negligible angular momentum being generated. This particular torque has a very small reactive ground reactive torque component and hence does not generate any appreciable angular momentum into the golfer/club ensemble.

Also where is the reference point for the calculation of the angular momentum of the system (I am interested - I like to fool with angular momentums)?

The earth constitutes the reference coordinate system for the calculations.

 

[drewyallop]

drewyallop,

Every action torque is accompanied by a reaction torque, Newton's third law. The wrist torque exerts an action torque on the club shaft but there is also an equal and opposite torque acting on the arms. Similarly for arms and shoulders, shoulders and midsection, midsection and hips, hips and legs , legs and earth.

One thing must be clearly understood – the internal torques generated by the golfer have eventually a reactive counterpart, small or large, relative to the earth. This reaction torque acts now as an external torque to the golfer/club ensemble and generates the angular momentum. Its is kind of strange but so be it.

The analysis shows that the proximal torques generate substantial angular momentum whereas torques more distal such as wrist torque, do less or practically not at all. They however do redistribute existing angular momentum, e.g., flowing from arms to club during the release.

Now more specifically your questions.



For the torque between mass m3 and m4 indeed there is negligible angular momentum being generated. This particular torque has a very small reactive ground reactive torque component and hence does not generate any appreciable angular momentum into the golfer/club ensemble.



The earth constitutes the reference coordinate system for the calculations.

I misunderstood Mandrin. I thought the rightmost graph showed the total momentum in the entire system, not just of the 3rd and fourth segments.

My question on reference point was badly phrased. As you know angular momentum is always calculated from a given reference point. I am curious to know the point since my experience is limited to relatively simple calculations e.g. single mass, orbits, projectiles. Maybe it would be better if you could show me your more detailed calculations in a pm, if you have time.

 

[mandrin]

Hey, mandrin... show drewy a complete FBD including "W" at the navel and how it's resolved statically (50-50 and even 60-40 weight distributions) through the legs into the ground... he deserves it. If you want to get fancy, you can even throw in some ground reaction thrust and torque at different phases of the golfswing. You can do it ....

SteveT,

Digging up some old files, there is one which seems to fit the request.

Weight Shift

 

[SteveT]

SteveT,

Digging up some old files, there is one which seems to fit the request.

Weight Shift

WELL... that should flummox poor drewy!!! I was thinking something simpler like a FBD with a "W" vector arrow vertically down through the navel and gonads, and the resolution of the force through the spread legs into the feet and then resolved into neat GRFs... horizontally and vertically. You should be able to throw that together in a snap and it would be so enlightening for your adulating ignorant fans... and a great scientific leap forward for golf lovers too. Only you have the facility to do that .... btw, do you have an index of angelfire links so we can create one convenient file of all your analytical musings ... I must have a dozen of them so far .... share...