|
Post by imperfectgolfer on Jan 7, 2012 18:08:57 GMT -5
I have viewed the BM Anti-Summit II video that is now available, and I think that it's very poor in terms of the quality of presentation, and it was another BM dog-and-pony show.
One of the worst presentations was Steve Nesbit's presentation of his hub path theory.
SN claims that the golfer exerts a "force" at the start of the downswing where the "force" is tangential to the hub path and that it is aligned with the longiitudianl axis of the shaft - orange arrow. I can readily accept that assertion - because the orange arrow is in the general direction of the hand arc path.
Then SN states that the "force" becomes more inwards-directed relative to the path by the early mid-downswing - red arrow. He doesn't describe what produces the "force" and why it becomes more inward -directed relative to the hand arc path.
Then, by the end of the mid-downswing and start of the early downswing (see the blue-dotted section of the hand arc path), SN claims that the "force" gets directed even more inwards - blue arrow. Again, SN doesn't describe what is producing that "force" and he doesn't explain why it is angled more inwards relative to the hand arc path.
Then, near impact, that "force" is directed centrally - green arrow, and it is due the golfer pulling-up on the club.
Now, nmgolfer has previously thought very highly of SN's hub path model, but I think that this is junk science. I think that the only force acting on the grip end of the club is directed in a direction that is parallel (in a curvilinear manner) to the hand arc path, and I believe that the club releases because the hand arc path changes directions constantly (and with a force that is proportional to the sharpness/acuteness of the hand arc path's circular motion - in other words, with a club-releasing force that is inversely proportional to the imaginary radius of the hand arc path).
I would like to see nmgolfer (or any other forum member) defend this SN hub path theory, which BM is now using for his RACP release explanation.
Jeff.
|
|
|
Post by imperfectgolfer on Jan 7, 2012 18:30:03 GMT -5
Later in his presentation, SN produced this explanation.
REMOVED
He produced that graph on the right - time on the X axis and magnitude of force on the Y axis. Vertical line represents impact.
He states that the "force" exerted by the golfer peaks at impact - although he doesn't specify what produces that force.
He then introduces a torque-force graph that peaks well before impact, and he seemingly believes that the golfer is actively torquing the club to induce the release - which fits in with BM's belief that the right hand produces a force-around-the-coupling point in order to get the club to release. Where does he get any "evidence" to support his assertion that a swinger is applying a positive torque around the coupling point in order to get the club to release?
Jeff.
|
|
|
Post by natep on Jan 7, 2012 18:39:06 GMT -5
Are you off your meds or what? Nesbit's forgotten more about science than you'll ever know.
|
|
|
Post by imperfectgolfer on Jan 7, 2012 18:49:42 GMT -5
Natep,
I have zero respect for you - because you have simply launched an ad hominem attack without presenting any comment re: golf swing mechanics/biomechanics. If you believe in SN's hub theory explanation, then you should be able to defend it by providing a counterargument. However, you virtually never present a counterargument that primarily discusses golf swing mechanics/biomechanics, and you have descended to the hysterical behaviour manifested by uncivilized boors like Footwedge.
Jeff.
|
|
|
Post by nmgolfer on Jan 7, 2012 19:30:02 GMT -5
Hi Jeff,
Just back from some skiing... don't you ski? I thought it was the law everyone must skin in Utah anyway...
I can't comment on Nesbit's presentation because i have not seen it nor do I intend to ever see it. But I can comment on what you said (he said).
1) We know exactly what force the club experience based on its motion. I can accept that the very first impetus may be mostly axial (with respect to the club shaft) but it quick starts pointing inward. The vector diagram in that write up I did you once had on your website show that the force MUST point inward.
2) Nesbit has a bio-mechanical model made using the best numeric tool we have for doing that sort of thing that can tell him (by way of back calculating from the kinematics i.e. measured motion (time & space) what the forces and torque were. That model was validate by all of the testing he did on all of those golfers. The math model is telling him what the forces and torques applied at the grip were.
I suspect he's speaking in generalities... Golfers generally apply torque (push pull between hands) early in the ds and by impact they're just holding on or in the case of better golfers pulling up.
|
|
|
Post by nmgolfer on Jan 7, 2012 19:33:15 GMT -5
Curious.... did Nesbit mention the shape of the hand path? Because that is key... it should be a tightening spiral during the last 2 of 3 stages.
|
|
|
Post by nmgolfer on Jan 7, 2012 19:36:47 GMT -5
P.S. The reason the path is an arc in the first place is because force is directed towards the instantaneous center of curvature. It is NEVER EVER simply "parallel" to the arc. This is basic high school physics and know as the "CENTRIPETAL FORCE REQUIREMENT". So sorry Jeff... you're dead wrong on that one.
|
|
|
Post by imperfectgolfer on Jan 7, 2012 19:42:25 GMT -5
nmg, I am fully aware of the CP-requirement (centrally directed force) that causes the hands to move in a circular direction rather than a linear direction, and the tighter the hand arc path curve (smaller the imaginary radius of the hand arc path) the greater the CP-requirement force. However, in the Nesbit hub path diagram, the radius of his hand arc path is remaining constant between P4 and P7, and yet he claims that the inward directed force is getting greater as the downswing progresses and that it is entirely directed centrally at impact. How do you explain that assertion? Secondly, here is your explanation. perfectgolfswingreview.net/New%20Millennium%20Golf%20Science.htmHere is your diagram. The blue arrow in your diagram represents the hand acceleration force (which causes the change in hand velocity vector from one instantaneous point in the hand arc path to the next instantaneous point). Surely, the hand acceleration force is directly proportional to the change in the radius of the hand arc path - the tighter the hand arc path curve (the smaller the imaginary radius of the hand arc path) the greater the magnitude of your blue arrow. Finally, the blue arrow in your diagram represents the CP-requirement force, while SN's arrow in his diagram seemingly represents the total force acting on the club (linear force + CP-force). Why should the total force become more inward-directed as the downswing progresses and eventually only be directed centrally at impact? Jeff.
|
|
|
Post by nmgolfer on Jan 8, 2012 0:06:08 GMT -5
CP = V^2/R velocity squared term requires the force to increase as the hands speed up even if radius is constant (which its not).
CP Force is inversely proportional to instantaneous radius and proportional to velocity squared. Consider for a second the one armed golfer. There is but one force acting on the grip so don't get confused by CP, linear and total force. There is ONE force a component of which is the centripetal force requirement.
I argue the force is NEVER directed at the center of curvature (which is contantly moving... it not fixed). This is why I say we should forget the concept of parametric acceleration because it implies something different happens in the last stages before impact. NO! Parametric acceleration is happening throughout the last two of three stages of the ds.
|
|
|
Post by imperfectgolfer on Jan 8, 2012 0:37:36 GMT -5
nmg,
You don't seem to understand what I have written.
You wrote-: "CP Force is inversely proportional to instantaneous radius and proportional to velocity squared. Consider for a second the one armed golfer. There is but one force acting on the grip so don't get confused by CP, linear and total force. There is ONE force a component of which is the centripetal force requirement."
I agree that there is only one force in an one-armed golfer and that is the "force" generated by the central torque generator that makes the left arm rotate about the fulcrum point of the left shoulder socket (which is not fixed in space but moves along its own small arced path). The left hand is simply the peripheral end of the rotating left arm, and it pulls the grip end of the club in a circular direction, and the movement of the left hand produces the downswing hand arc path. That "force" that moves the left hand along its hand arc path in the downswing is surely directed along the path of the hand arc path. That "force" can be divided into two conceptual forces - a CP-force directed centrally and a linear force that is tangential to the hand arc path. So, what exactly is the "force" that SN is talking about and how it can change direction as previously described.
By the way, SN did talk about the hub path getting smaller in radius nearer impact due to parametric acceleration - biomechanically due to elevation of the left shoulder socket. SN stated that this was a minor force that could accelerate the club just prior to impact - like cracking a whip by pulling up on the handle of the grip. SN also stated that in his hub path model, he included this parametric acceleration, but he also stated that in his study of individual golfers that some golfers significantly manifested this phenomenon while other golfers had very little parametric acceleration. Either way, the parametric acceleration phenomenon is a minor element in SN's hub path model (that only occurs near impact) and it does not explain what is causing/happening with respect to the SN-described "force" that the golfer generates to move the club throughout the entire downswing, and you have not explained why SN believes that it becomes progressively more inward directed during the later downswing and then directed centrally at impact. In fact, you previously mocked BM when he proposed this explanation - but I have now discovered that it comes directly from SN.
Jeff.
|
|
|
Post by nmgolfer on Jan 8, 2012 11:07:23 GMT -5
Jeff I have not seen the video nor do I ever intend to waste my time watching it therefore I cannot comment on what SN did or did not say.
You're right ... I probably don't understand what you are trying to say but whose fault is that? Not mine. There is one force at the grip. At the top when hand velocity is practically nil it can be predominantly axial (in the shaft direction) but as hand velocity increase that force MUST become proportionately large and directed inward. This is because cp is proportional to hand velocity squared.
The Parametric Accel deception:
With regards to parametric acceleration... The only way to increase the angular acceleration of the club is to have a component of THE FORCE that is not directed at the center of rotation. Where the club fully released (lined up) and you apply force in the direction of the center of rotation, it would have NO EFFECT other than to lift the club. It WOULD NOT acceleration clubhead or increase angular acceleration. Therefore speaking of parameteric acceleration is stupid because it implies something different is happening near impact. NO... we apply parametric acceleration for MOST OF THE DOWNSWING.
On calling a spade a spade:
I will continue to mock the BM when its clear to me he does not understand something which is most of the time. It makes no difference if he is parroting Dr. Nesbit or not. That said I would be surprised if SN is "confused" but I would not be surprised if he's not communicating effectively the to the laymen audience.
Getting to root cause:
One more point. I focus on the Club... how does a golfer get that clubhead to impact with the most clubhead speed and as efficiently as possible? To the end I don't care what the body does. I do care what forces torques paths and velocitiy profies the body applies to the club. The answer is a sprial with some judiciously applied torque and no slowing prior to impact. How the body accomplishes that is up to each golfer and each method teacher to decide.
|
|
|
Post by nmgolfer on Jan 8, 2012 11:23:29 GMT -5
OK Jeff,
Having re-read your posts several times let me add this... Yes... it is the component of force that is tangent to the path the accelerates the club "along" the path. Then there is the fact that the "line of action" of the force at the grip is not directed through the center of gravity of the club which causes angular acceleration. So there are two pieces which result in club head velocity.
Vclubhead = Vhands + Vrel where
Vrel is relative velocity = Club length * angular velocity.
Its the torque (torque = force * perpendicular distance to the club CG) that the force (not being directed through the CG) which increases angular velocity which is the predominate source of clubhead speed.
Frankly it sounds to me like Nesbit is saying it right. I think you still do not understand it. (I tried like hell to explain the mechanics of release to you years ago and am dismayed to see that it apparently never sunk in... I give up)
|
|
|
Post by imperfectgolfer on Jan 8, 2012 11:36:33 GMT -5
nmg,
You wrote-: "Frankly it sounds to me like Nesbit is saying it right. I think you still do not understand it. (I tried like hell to explain the mechanics of release to you years ago and am dismayed to see that it apparently never sunk in... I give up)"
I am glad that you are giving up - because I think that you seemingly have nothing useful to contribute other than your original idea about the hand release (which I think is rational).
Jeff.
|
|
|
Post by imperfectgolfer on Jan 8, 2012 12:10:45 GMT -5
Here are more reasons why I reject the SN hub path model, which is purely a theoretical model. BM is holding the golf club - positioned in the early downswing, and SN is holding the yellow arrow to signify that the "force" is pulling the club at a tangent to the hand arc path and in the general direction of the axis of the clubshaft. Note that BM is at the start of the mid-downswing. Now SN is pointing the arrow more inwards - stating that the "force" is directed more inwards, although he doesn't explain why the "force" is directed more inwards (relative to the hand arc path). This more inwards-directed "force" is not representing the CP-component of the "force" moving the grip end of the club (as nmg has implied in his post) Next, SN claims that there is a torque force around the coupling point being produced by the right hand pushing against the aft side of the club. The red dot represents the coupling point, and the blue arrow shows a torque force being exerted around the coupling point by the right hand. Note in the background, there is small arrow on his diagram showing the "force" directed inwards, but there is no torque force yet drawn in the diagram. Then, SN modified his diagram to show the torque force. Note that he has drawn the torque force working around the coupling point (labelled T) which he claims is being exerted by the right hand pushing on the club in order to induce the club to release. He claims that this torque force reaches its maximum value at P6.5 and then drops to zero by impact. At impact, he states that the only force acting on the club is the "force" that is now directed inwards. He states that there is no forward force needed to accelerate the club anymore because golfers maximize their clubhead speed at impact. This hub path model (which is purely theoretical) may partly explain a swing-hitter's action, but it doesn't explain a swinger's action. The blue arrow represents the release of PA#4 - and it causes the left arm to swing in a circular manner around the fulcrum point of the left shoulder socket (which moves in space to a finite degree during the downswing). That is the only "force" moving the left hand, which follows the path represented by the red arrows. The club passively responds to the hand arc path and it passively develops angular momentum - according to nmg's explanation (Vclubhead = Vhands + Vrel). The right hand does not actively push against the aft side of the club in order to induce, or facilitate, the release of the club in a swinger's action. The only "force" acting on the grip end of the club is due to the left hand's motion along its hand arc path. That "force" (which is due to the active release of PA#4) does not end at impact. It ends at P7.5 - note that I have drawn the end of the blue arrow as going past the impact position to the P7.5 position. That means that a swinger is still exerting a forward-pulling force on the grip end of the club from P7 to P7.5. That "force" is not designed to accelerate the clubhead after impact because the clubhead has reached its maximum speed at impact, and it is designed to allow a golfer to maintain an intact LAFW/FLW from P7 to P7.5 and thereby avoid post-impact flipping while the club is still traveling in the immediate impact zone (which extends to P7.2). The same principle applies to a back-handed tennis stroke action - which mimics a swinger's action. Roger Federer is stroking the ball and the forward momentum of his right hand doesn't stop at impact (image 4) but it continues non-stop to image 5. That allows Roger to avoid flipping of his lead wrist. Jeff.
|
|
|
Post by natep on Jan 8, 2012 16:15:58 GMT -5
Look at this diagram from Miura's parametric acceleration papers, showing hand force vectors and the tangential and radial (or what BM calls "normal") components. He is reporting force vectors exactly like Nesbit. I suppose this is junk science as well, right Jeff?
|
|