|
Post by dubiousgolfer on Aug 16, 2020 7:29:04 GMT -5
DG, DT stated the following-: " But there is a consequence when we try for orbital motion. For the club to orbit around the hands, the CoM has to move. In order to achieve an angular acceleration of A radians/sec/Sec, the CoM has to achieve a linear acceleration L of R*A (where R is the radius, the distance from MHP-A to CoM). That linear acceleration requires a force to produce it. And the only thing in the diagram putting force on the club is the hands. So the hands are not just applying a couple for orbital motion; they are applying a couple PLUS an extra force from the hands." If I understand DT correctly, then for the club to orbit the hands (which is what happens in the downswing) an "extra force" (other than the hand couple) must be in play. If that "extra force" is causing the club to gain angular velocity as the club orbits around the hands, then why is there any need for the hand couple to be in play? Jeff. Dr Mann If we are in agreement that the hand couple has no effect on the movement of the COM , and is not an effective clubhead speed producer (ie. just spinning the clubface around the clubs COM) , then maybe its just related to anatomy/geometry . It could be a reactive effect like that 90 degree wristcock stopper in the DP and (maybe later in the downswing) somehow related to an anatomical requirement to get the club moving on its 'functional plane' just before P6 (ie. some limitation in a joint's freedom of movement similar to having to uncock the lead wrist as it goes into flexion but without moving the clubs COM- if that's possible). DG PS. It might also relate to a 'geometrical' requirement like a change in the spatial alignment of the club without the need to move the COM of the club.
|
|
|
Post by dubiousgolfer on Aug 16, 2020 17:45:41 GMT -5
Dr. Mann, The animations of the double pendulum on DT's site must be doing something wrong as well. The clubhead seems to rise above the horizontal starting position at the top of the swing. Perhaps the "intentionally created 90 degree wristcock" for purposes of the animation and modeling is the reason. www.tutelman.com/golf/swing/golfSwingPhysics2.phpS Hi S You have to take into account what Rod White said near the start of that chapter for the non-driven DP. "Initially the system rotates at a constant speed, and the string stops the clubhead from swinging out. No energy is put into the system for this model; the system is rotating to begin with, and continues to rotate under its own inertia.So there are no 'hand forces' being exerted for the 'non-driven' DP animation, no 'Net Force' across the club and therefore no 'MOF' . For the Driven DP - he mentions "Here, during the initial build up of speed, some sort of "brace" (providing positive torque) is needed prevent the club from being pulled inward.". That suggests to me that there is an initial 'Net Force' across the club which causes a 'negative MOF' at the start of the downswing which has to be offset by that 'brace' with a positive stopping torque. But then he also says "the golfer holds the club in a cocked position and accelerates the shoulders and torso." . I'm assuming this is to prevent the club releasing after the 'MOF' (caused by the Net Force across the club) moves from negative to positive as the downswing progresses. DG
|
|
|
Post by imperfectgolfer on Aug 16, 2020 18:25:03 GMT -5
DG, According to DT and SMK, the hand couple phenomenon does not cause linear acceleration of the COM and I can now both understand and accept that point. I can also now understand how a hand couple phenomenon can cause the club to rotate around its COM if there is no friction and if the club is just a "free body" floating in space. However, in a golf swing we have no intention of causing the club to rotate around the COM, and we specifically want the club to rotate around the lead wrist hinge joint during a PA#2 release action. DT asserts that an "extra force" is needed to release the club and I can agree with that assessment. I previously believed that a PA#2 release action would not require "extra force" and that it would happen automatically/naturally according to the D'Alembert principle. However, when I saw the small MoF values that exist at about P5.2 - P5.5 in Dr. Kwon's graphs, I realize that I was wrong and I now believe that an "extra force" is required. My present intellectual position is that the "extra force" can be derived by the left/right hand pushing against the aft side of the club in such a manner as shown in this Kwon image.
Note the way that Dr.Kwon has drawn the blue and green arrows to show the forces produced by the two hands. They are both working in a "force-across-the-shaft" manner and not as a hand couple (where the two forces are equal in amplitude but directly opposite in direction - as you depicted in your diagram of the hand couple phenomenon). Both of those blue/green forces are promoting a left wrist uncocking (PA#2 releasing) phenomenon where the club will rotate counterclockwise. I now envisage that the magnitude of these two forces must be roughly equal to the force promoting a clockwise rotation of the club due to the MoF phenomenon existing between P4 => P5.2 and that allows the degree of lag to remain essentially unchanged. I now also imagine the force-across-the shaft ("extra force") value peaking at ~P5.2 - P5.5 and then decreasing after P5.5 at the same time as the MoF value starts to increase in magnitude and that is when the club starts to release in earnest. I am still unsure of exactly why the club releases at P5.2 - P5.5 in most pro golfers and I suspect that it is due to a complex interplay between the "extra force" and the changing MoF values and the fact that the right arm is fully adducted at that time (thereby inducing the start of a right arm straightening action).
It may be worthwhile sending SMK and DT and Dr. Kwon a copy of that Kwon image (above) where the two forces are working in the same "force-across-the-shaft" direction, and not in opposing directions, and then ask them how it can represent a hand couple phenomenon (as depicted in your diagram) where the two forces are exactly equal in magnitude, but directly opposite in direction.
Jeff.
|
|
|
Post by dubiousgolfer on Aug 16, 2020 21:08:50 GMT -5
Dr Mann Those Dr Kwon diagrams are just representative examples for the viewer to understand the maths later in that document. This is what he said in that document (link below). www.drkwongolf.info/technotes/mh_kinetics.pdf" Figure 1 shows the forces acting on the grip by golfer’s hands. The small arrows in Figure 1A are the grip forces acting on the club by the hands. Let's assume here that we have a grip force measurement system consisting of an array of force sensors covering the entire grip. Then each sensor will pick up the force acting on it and we end up with a large number of small grip forces with varying magnitudes and directions. In reality there is no reliable and validated grip force measurement system available at the moment and it is almost impossible to accurately measure these forces directly. Since it is impossible to measure these forces directly and accurately, this individual force perspective is not that useful."Also the real life measurement of those forces across the shaft (the Koike and Choi graphs) show left and right hand forces virtually identical in opposite directions, therefore those green arrows show in Dr Kwon's diagram should be in the opposite direction. DG PS. I can easily imagine there might be a positive net torque caused by the hands from P5.2-P5.5 If you look at graph (c) , and compare it to the avatars, there are positive torques being applied by each hand from around P5.2 - P6.5 (mainly by the left hand). Further, look at graphs N and R below from Choi also showing positive torques applied by each hand and they never go below zero until later in the downswing , probably after P6.
|
|
|
Post by dubiousgolfer on Aug 17, 2020 6:45:08 GMT -5
Dr Mann
Although I said I could easily 'imagine' positive torques (mainly in the left hand for Koike's golfer 2nd golfer) , I am assuming that both Koike and Choi's graphs (that I mentioned in my previous post) are mathematically estimated 'couples' in each hand. If that is the case, then they will not move the COM of the clubhead or release PA#2 .
I am basically saying that I can 'imagine' each hand does not apply 'couples' but 'torques/moments' that are caused by unequal forces across the shaft ( within each hand) to assist in the initial release of PA#2 and I doubt it will have a significant increase on clubhead speed (for the very short time period it may be applied).
DG
|
|
|
Post by syllogist on Aug 17, 2020 7:22:41 GMT -5
Hi DG, I reviewed SMK's video links below. They're fairly straight forward. vimeo.com/158856998 (In-Plane Couple) vimeo.com/158419250 (Intro to Club Kinetics) The first video makes it apparent that the moment of force of the club takes over as compared to the force of the couple at about shaft horizontal where applied force cannot increase the angular speed of the clubhead. Further, one might better consider the torso as a force couple that gives angular velocity to the arms which gives angular velocity to the club. The second video shows the assumption of the a net positive couple (right hand force in excess of left hand force) that causes the club's center of mass to move upward at the start of the downswing. It appears to me that in order not to allow the club's center of mass to move upward at the start of the downswing, wristcock would have to increase (from the already maximum wristcock position). If the true forces that can be measured at each hand are unequal, I don't think that such has any significance in terms of the dynamics of a swing. S
|
|
|
Post by imperfectgolfer on Aug 17, 2020 11:04:46 GMT -5
DG, You wrote-: " Also the real life measurement of those forces across the shaft (the Koike and Choi graphs) show left and right hand forces virtually identical in opposite directions, therefore those green arrows shown in Dr Kwon's diagram should be in the opposite direction." I think that you are wrong to state that the arrows drawn in that Kwon diagram are incorrect. It is very difficult to imagine that Kwon made such an elementary mistake. I can think of an explanation that explains why the green arrows are drawn in that way - directed downwards and outwards when the hands are roughly at the P5 position. Look at figure 3 in that Kwon article that you referenced and note that the net mid-hand force (black arrow) is directed downwards-and-outwards. Here is a copy of that Kwon figure 3 image. I think that at P5, the left hand is pulling the club handle down the hand arc path, which is still oriented downwards-and-slightly backwards (away from the target). At the same time, the right hand is applying an "across-the-shaft" force that is directed in a left wrist uncocking (counterclockwise) direction. Here again is Kwon's image of the net mid-hand force/torque. Just below that image, Kwon wrote the following-: "The net mid-hand force and torque represent the overall linear and angular interactions between the hands and the club". In other words, it does not only represent the hand couple forces/torques.
You also stated -: "I am assuming that both Koike and Choi's graphs (that I mentioned in my previous post) are mathematically estimated 'couples' in each hand. If that is the case, then they will not move the COM of the clubhead or release PA#2." If the left hand's and right hand's "force-across-the-shaft" forces are simply balancing each other out in a hand couple manner and if the hand couple cannot be causally responsible for moving the club's COM or releasing PA#2, then you are seemingly claiming that the hand couple has no role in inducing the counterclockwise rotation of the club that happens during the downswing between P4 => P6?
If I am surmising your "thought process" correctly, then how do you explain what Kwon is implying in the following image. Note that the net MH moment is positive between P4 and P6, and it is causally responsible for inducing a counterclockwise rotation of the shaft. What other explanation do you have for the club gaining angular momentum that increases the angular velocity of the club between P4 => P6 and causes it to rotate in a counterclockwise direction? It cannot be due to the MoF factor because it will cause the club to rotate clockwise, and not anti-clockwise - as seen in the following Kwon image. Note that club torque due to the net MH force is negative between P4 => P5.5, so it cannot be responsible for any counterclockwise rotation of the shaft happening between P4 => P5.5. Try a simple experiment. Position your hands on the club handle at the P5 position with 90 degrees of lag. Then apply a positive hand couple torque by pulling the club handle in a direction towards the target with the left hand while pushing against the aft side of the target with the right hand in a direction that is away from the target while allowing the club to move in space. Does the club not rotate counterclockwise in a left wrist uncocking direction? You also wrote regarding the Koike graphs-: "If you look at graph (c) , and compare it to the avatars, there are positive torques being applied by each hand from around P5.2 - P6.5 (mainly by the left hand)." You seemingly believe that the hand couple is applying a positive torque to well beyond P5.5, and actually all the way to ~P6.5. How do you reconcile that belief with this Kwon graph below. Note that the mid-hand torque becomes negative after P6. In fact, in the zoom 2 conference hosted my Michael Finney, Kwon stated that the hand couple torque often becomes negative even earlier around P5.5 in some pro golfers. Here is Kwon's graph for the torques found in 5 pro golfers (top left hand graph).
The red graph crosses the zero line at just before P6 - see avatar's position. Jeff.
|
|
|
Post by dubiousgolfer on Aug 17, 2020 22:20:55 GMT -5
Dr Mann I've been reading Dr Kwon's web article again but I think there needs to be confirmation of the terminology he is using: The 'Net Mid Hand Moment ' is the 'hand couple' . The 'Net Mid-Hand Force' is just the 'Net force' The 'MH Force Moment ' is the MOF caused by the 'Net MH Force' or 'Net Force' The graph below is the 'Net Mid Hand Moment' (ie. Hand Couple) and does not contribute to movement of the the COM of the club - only causes club rotation about its COM. The red circles just represent a convention for identifying the 'moment' (in this case the 'moment' of the hand couple) around the mid-hand point and is not describing some physical rotation of the hands around the mid-hand-point. This other graph below shows the 'MH-Force Moment' (MOF caused by the Net Force) but for some reason is showing a 'Moment' (ie. green circular arrows) around the COM of the club (why has he done that?). Relating to my question above , he also says the following just before this graph. "In the perspective of the club, the net MH moment is not the only moment acting on it (Eq. 11). Figure 5 shows the swing‐axis component of the moment produced by the net MH force about club’s COM (let’s call this as the ‘MH force moment’) in the moving MH reference frame.
I hope he is not implying the same 'non-intuitive' issue we had with the hand couple, that the 'MH force moment' is only spinning the club around its COM (surely not?). Here is the graph showing : 1. The 'Net Mid Hand Moment ' (hand couple) - red graph 2. The 'MH Force Moment' (ie. the MOF caused by the Net MH force or Net Force) - Green Graph (he labels it as the 'T-MH Force') 3. The 'T-Net' is the blue graph and is the sum of 1 and 2 above. This is what he says (MD is P6). " The net MH moment and the MH force moment are in general antagonistic, acting in opposite directions to each other all the time except a short time period before event MD. For most part of the downswing, the net MH moment promotes rotation of the club in the swing direction while the net MH force inhibits rotation of the club. Near the impact, however, their roles switch. Club rotates quite fast near event MD and the couple action of the hands starts interfering with club’s rotation here. The net torque which is responsible for angular acceleration of the club largely remains positive (counterclockwise) but turns to negative right before the impact"For the short period before P6 , PA#2 releases for some reason and its not the MOF (which is promoting negative moment ) or the hand couple (which doesn't move the COM) . Therefore can one assume the club is just 'freewheeling' on its own angular momentum (no torque being applied for a very short time period) that is uncocking the left wrist while the hand couple moves from positive to negative torque (and MOF moving from negative to positive)? You mentioned the following : "Note that the net MH moment is positive between P4 and P6, and it is causally responsible for inducing a counterclockwise rotation of the shaft."The 'Net MH Moment' is defined as the 'hand couple' (if I'm not mistaken) and all it will do is cause a counterclockwise (or clockwise) rotation of the shaft around its COM . Looking at Dr Kwon graphs I am probably mistaken in imagining the possibility of positive torques being applied via the wrists to assist PA#2 release before P6. You also said "If the left hand's and right hand's "force-across-the-shaft" forces are simply balancing each other out in a hand couple manner and if the hand couple cannot be causally responsible for moving the club's COM or releasing PA#2, then you are seemingly claiming that the hand couple has no role in inducing the counterclockwise rotation of the club that happens during the downswing between P4 => P6?" No - the hand couple does induce counterclockwise rotation of the club but only around its COM. It also induces a negative couple that will tend to try and rotate the club in the clockwise direction around its COM after P6. DG
|
|
|
Post by imperfectgolfer on Aug 17, 2020 22:51:48 GMT -5
DG, You stated that you do not believe that the hand couple (which Kwon calls the "net MH moment") causes the club to develop angular momentum around the hands between P4 and P6. You also stated that "For the short period before P6 , PA#2 releases for some reason and its not the MOF (which is promoting negative moment ) or the hand couple (which doesn't move the COM) . Therefore can one assume the club is just 'freewheeling' on its own angular momentum (not any torque) that is uncocking the left wrist while the hand couple moves from positive to negative torque?" Regarding your bold-highlighted statement, you assume that the club is just "freewheeling" on its own angular momentum. I don't understand how a club can generate its own angular momentum without a positive torque being applied. Please explain how this is possible. Consider this image that you referenced. You also quoted the following regarding that image-: "For most part of the downswing, the net MH moment promotes rotation of the club in the swing direction while the net MH force inhibits rotation of the club'. From my perspective, that quote implies that the net MH moment promotes rotation of the club in the swing direction (counterclockwise direction) by applying a positive torque, which surely means that it is causally responsible for any angular momentum that the club acquires between P4 => P6 in a counterclockwise direction. I cannot envisage that the club gains angular momentum in the absence of any positive net torque! How is that possible? Jeff.
|
|
|
Post by dubiousgolfer on Aug 18, 2020 8:59:37 GMT -5
Dr Mann "You stated that you do not believe that the hand couple (which Kwon calls the "net MH moment") causes the club to develop angular momentum around the hands between P4 and P6"
No! The hand couple can generate 'Spin Angular Velocity' and 'Spin Angular Momentum' (without moving the COM of the club). Look at the diagram below where the NET force (I've not shown it or the MOF effect for the sake of simplicity) is responsible for moving the clubs COM down the dotted line. While this is happening imagine a 'Hand Couple' being applied (ie. the F forces) . Can you see how the 'club' is being 'angularly accelerated' around the COM? The 'Hand Couple' is not moving the COM but responsible for spinning the club around its COM. You said "I don't understand how a club can generate its own angular momentum without a positive torque being applied. Please explain how this is possible."
Yes, you are correct! For the club to be freewheeling with its already accumulated angular momentum , what is creating that angular momentum in the first instance? Then it must be the 'Hand Couple' and 'MOF' combined, and if the MOF is negative up to P6 , then it must be the 'Hand Couple' that is generating that positive 'spin angular momentum' like the diagram above shows. DG PS. On reflection, when looking at that diagram , it seems that the wrists and arms must move in such as way as to not impede the 'Hand Couple' effect on generating 'Spin Angular Momentum'. Maybe the uncocking of the lead wrist is one aspect of a biomechanical facilitation required to allow the 'Hand Couple' to do its job efficiently. Personal Notes For My Reference only (relating to the physics). 1. Complex motion of golf club can be reduced to a 'Force' through its COM and a 'torque couple' around its COM (Chasles Theorem) 2. Once you have point 1 , there is a requirement to move that 'Force' going through the COM to a new point to reflect a closer reality to where the golfer would apply that force (Mid-Hand-Point). Leave the 'moment of a couple' around COM unchanged until later. 3. The method for doing point 2 is by using a mathematical method for replacing the original force (applied to its COM) with an 'equivalent force + couple ' applied 'through/around' the mid-hand point . **** But a couple applied anywhere on the golf club will not cause the COM to move**** 4. We can now move the couple around the original COM in point 1 (ie. around the COM) to the mid-hand point (its effect on the golf club remains the same). 5. What we have at the mid-hand-point is a 'Force' + 2 couples (the original in point 1 + point 3) . **** But a couple applied anywhere on the golf club will not cause the COM to move**** Question: So why does the 'Net Force' in SMK's 'Intro Kinetics' video show the COM of the club seemingly aligning with the tail vector of the 'Net Force' ? Theoretically , this cannot happen with the 2 'hand couples. It is the 'Net Force' components that are moving the COM to align with the tail end of the vector while the hand couples are spinning the club around its COM.
|
|
|
Post by dubiousgolfer on Aug 18, 2020 10:10:07 GMT -5
An example that SPIN angular momentum is being created can be demonstrated if you swung as normal and then just threw the club to a target. What would you see happen?
The club spins around its own COM in the air and that is a demonstration of the conservation of angular momentum (which proves that the club had spin angular momentum before it was released into the air- ie. the hand couple).
I'm now also uncertain whether the MOF is also causing 'Spin Angular Momentum' and I refer back to DT's email where he said:
"If we want an orbital motion, we want the club to spin about the hands, not about its CoM. BUT... that requires the CoM to move. Let's impose on this a great truth of Newton's Laws: the laws of forces and torques act on the CoM.
The underlined suggests to me that any 'torque' (including the applied MOF) acts around the COM but I need to investigate this more.
Here's a video showing spin angular momentum as an object is thrown in the air .
DG
|
|
|
Post by syllogist on Aug 18, 2020 11:27:18 GMT -5
Hi DG,
Isn't the moment of force the rotational result of a force acting on an object (angular movement of the object) and the force we're discussing is a force couple? Also, doesn't the moment of force increase during the downswing as the arms and club move farther from the center of rotation (point on the torso)?
S
|
|
|
Post by dubiousgolfer on Aug 18, 2020 13:11:50 GMT -5
Hi S It looks like the MOF does cause the COM of the club to rotate (see Sasho video screen image below). The 'hand couple' we were discussing is responsible for the positive torque from P4 to P6 does not move the COM but rotates the club around its COM as per my previous diagram. The instantaneous CENTRE OF ROTATION of the golf clubs COM is in Dr Kwons website (link below- Fig 4- Green Line) but no graph comparing MOF (about mid-hand point) vs COR. www.drkwongolf.info/technotes/mh_kinetics2.pdfDG
|
|
|
Post by imperfectgolfer on Aug 18, 2020 14:09:26 GMT -5
DG,
You wrote-: "Look at the diagram below where the NET force (I've not shown it or the MOF effect for the sake of simplicity) is responsible for moving the clubs COM down the dotted line. While this is happening imagine a 'Hand Couple' being applied (ie. the F forces) . Can you see how the 'club' is being 'angularly accelerated' around the COM? The 'Hand Couple' is not moving the COM but responsible for spinning the club around its COM."
No! I cannot see that happening.
First of all, the club's COM does not move downwards vertically, but at angle dependent on the shape of the hand arc path and the degree of lag. Secondly, I cannot envisage the club being angularly accelerated around the COM because the proximal end of the club is attached to the hands which prevent it from rotating around the COM. The club handle has to go where the hands are going and any angular momentum gained by the club must come from forces operating at the level of the hands, while producing an effect at the level of the left wrist hinge joint.
Jeff.
|
|
|
Post by syllogist on Aug 18, 2020 16:22:30 GMT -5
Hi DG,
I agree with your diagram in that the center of mass of the club will try to line up in the direction of the force. What makes this challenging for me is that we have a double pendulum that is not only rotating around an imaginary point on the chest but is also rotating around the hands at some point.
To think through a force couple and moment of a force, I visualize a 12" cylindrical bar placed on a table. I push one end of the bar with my hand. My hand acts like a force couple and the push provides the force to rotate the bar around its center of mass (found exactly 6" from the end of the bar). The center of mass does not move.
Since I am pushing the extreme end of the bar, the moment of a force is greater than if I were to push the bar at a point 1" from the center of the bar. The moment of a force does not rotate the bar but describes how easy it is to rotate the bar.
Does the moment of a force mean something different in the double pendulum model?
S
|
|