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Post by imperfectgolfer on Sept 13, 2020 10:54:00 GMT -5
See this Jon Sinclair video at - What is causing the peripheral clubshaft to bend forward during the later stage of his arm straightening action? Jeff.
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Post by dubiousgolfer on Sept 14, 2020 19:11:32 GMT -5
Dr Mann
In that particular video JS does apply some positive torque on the grip . This will cause the shaft to bend and deform from its initial rest position (ie. shaft bent backwards).
As JS stops his hand moving forward , there is still an existing restoring force (because of the elasticity of the deformed backwards bent shaft) which will cause the clubs COM to overshoot its neutral position and this will cause forward bend.
In simple terms this would be a 'rebound' effect .
DG
ps. Note that as soon as the shaft bends forwards , it also means that his hand is applying a negative torque.
What point is JS trying to prove in that video? Does it relate to the ongoing dispute with Jacob/Manzella claim that positive torque is applied by the hands approaching impact?
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Post by dubiousgolfer on Sept 15, 2020 7:08:36 GMT -5
I am suspecting JS's video is related to this 'dispute' going back and forth between the 2 camps .
I actually found another video by JS including comments from Brian Manzella and Jacobs.
DG
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Post by imperfectgolfer on Sept 15, 2020 16:30:56 GMT -5
Dr Mann In that particular video JS does apply some positive torque on the grip . This will cause the shaft to bend and deform from its initial rest position (ie. shaft bent backwards). As JS stops his hand moving forward , there is still an existing restoring force (because of the elasticity of the deformed backwards bent shaft) which will cause the clubs COM to overshoot its neutral position and this will cause forward bend. In simple terms this would be a 'rebound' effect . DG ps. Note that as soon as the shaft bends forwards , it also means that his hand is applying a negative torque.What point is JS trying to prove in that video? Does it relate to the ongoing dispute with Jacob/Manzella claim that positive torque is applied by the hands approaching impact? I can understand a rebound phenomenon causing the peripheral clubshaft to bend forward during the later phase of the right arm straightening action, but how can you imply a negative torque at the level of the club handle if the right triceps muscle is still contracting and causing straightening of the right arm that causes his right hand to still be moving away from his right elbow (albeit at a much slower speed)? Jeff.
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Post by dubiousgolfer on Sept 15, 2020 16:57:58 GMT -5
The clubheads angular velocity is moving faster than his right hand, even while its straightening , therefore its passively restricting the angular velocity of the club (ie. negative torque).
DG
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Post by imperfectgolfer on Sept 15, 2020 17:50:33 GMT -5
The clubheads angular velocity is moving faster than his right hand, even while its straightening , therefore its passively restricting the angular velocity of the club (ie. negative torque). DG I can understand the "idea" that a negative torque phenomenon exists with respect to the clubhead end of club, but the golfer is still applying a positive torque to the club handle. Jeff.
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Post by dubiousgolfer on Sept 15, 2020 19:24:28 GMT -5
I suspect one can test it out by holding a long flexible stick in one's hands and bending its peripheral end 'forward' on some door frame . 1.Your hands will feel a positive torque being applied by the handle (ie. in a real golf swing this would be due to the fact that the handle is moving at a faster angular velocity than the hands). 2.The handle (if it had any feelings) would feel a negative torque being applied by the hands Points 1 and 2 are a rotary analogue of Newtons Third Law. If object A (handle) exerts a torque on object B (hands) about a given axis, then B(hands) exerts an equal but opposite torque on A (handle) about the same axis. This is explained by DT's image below. DG
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Post by imperfectgolfer on Sept 15, 2020 20:52:17 GMT -5
I suspect one can test it out by holding a long flexible stick in one's hands and bending its peripheral end 'forward' on some door frame . 1.Your hands will feel a positive torque being applied by the handle (ie. in a real golf swing this would be due to the fact that the handle is moving at a faster angular velocity than the hands). 2.The handle (if it had any feelings) would feel a negative torque being applied by the hands Points 1 and 2 are a rotary analogue of Newtons Third Law. If object A (handle) exerts a torque on object B (hands) about a given axis, then B(hands) exerts an equal but opposite torque on A (handle) about the same axis. This is explained by DT's image below. DG I disagree with your reasoning. How can one bend the peripheral clubshaft forward using a door frame - other than by applying a torque on the club handle in a negative direction against the resistance of the door frame? However, that scenario does not apply to what is happening in a golf swing where there is no door frame present. I also don't like your reasoning regarding Newton's 3rd law. You state that the club handle exerts a force on the hands after P6 - but that is only due to the fact that the COM end of the clubshaft has gained a lot of momentum before P6 that causes the peripheral clubshaft to bend forwards after P6. I think that you are not considering the other major force in play - the hands exerting a force on the club handle. During the P6 => P7 time period, when the peripheral clubshaft is bent forwards, the hands are still pulling the club in a targetwards direction and exerting a MoF torque that is positive. When viewed from the perspective of what is happening at the level of the hands on the club handle - I think that one is still trying to apply a positive torque, even though the released COM end of the clubshaft being bent forward implies that a negative torque scenario applies when one thinks of the relationship between the peripheral clubshaft and the proximal clubshaft. From the "feel" perspective of the club handle, I can imagine it "feels" a negative torque if the peripheral clubshaft is bent forward.
Jeff.
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Post by dubiousgolfer on Sept 15, 2020 22:26:10 GMT -5
The stick/doorframe example is to prove that the forward bend requires a negative torque applied by the hands (whether in a static position or dynamically like a golf shaft's leading bend approaching impact).
I think SMK's pragmatic MOF explanation does not reflect the reality of all the forces required to move the COM of the club around the 'mid-hand-point'. So do you believe that the Koike and Choi graphs (which show net negative torque in the hands approaching impact) are flawed? They reflect the data measurements using an instrumented grip and not 'feels'.
DG
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Post by imperfectgolfer on Sept 15, 2020 23:55:06 GMT -5
The stick/doorframe example is to prove that the forward bend requires a negative torque applied by the hands (whether in a static position or dynamically like a golf shaft's leading bend approaching impact). I think SMK's pragmatic MOF explanation does not reflect the reality of all the forces required to move the COM of the club around the 'mid-hand-point'. So do you believe that the Koike and Choi graphs (which show net negative torque in the hands approaching impact) are flawed? They reflect the data measurements using an instrumented grip and not 'feels'. DG I will repeat what I have already stated - the club handle will measure a negative torque between P6 => P7 because the peripheral club is traveling faster than the club handle, even though the hands are still applying a positive MoF during that same time period. By the way, I don't believe that the club's COM rotates around the mid-hand point, and I believe that it rotates around the fulcrum point of the left wrist joint. Jeff.
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Post by dubiousgolfer on Sept 16, 2020 7:01:30 GMT -5
Dr Mann
Yes, that makes sense. SMK said the same in his 'In Plane Couple' video that even though there is negative torque measured in the hands , the 'in plane' MOF component caused by the 'Net Force' will still be angularly accelerating the clubhead.
I no longer try to visualise the SMK MOF concept because I do not think its wholly correct from a physics standpoint. I disagree with SMK that a linear force alone applied at the 'mid-hand-point' (or the via the 'fulcrum point of the left wrist') can cause a rotation (torque effect) of the clubs COM (about that fulcrum point or mid-hand-point). His concept might make it easier and more pragmatic to explain the golf swing to non-physicists (just like DT uses the 'Centrifugal' force concept) but it doesn't appeal to me anymore.
The fact that I cannot find any mention of this MOF , that replicates his 'Intro Kinetics' video, anywhere on the web causes me to doubt its accuracy (solely from a physics standpoint).
DG
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Post by dubiousgolfer on Sept 16, 2020 9:39:34 GMT -5
Dr Mann
Don't you have some doubts about SMK's MOF concept?
For example:
1. The only force that can be applied to the club is via the hands. 2. If you regard the point about which the 'Net force ' is applied being the 'fulcrum point of the left wrist' then that means you are assuming that the MOF (caused by a component of that Net force within the swing plane) is somehow causing a positive torque on the club via the hands. What else is in contact with the club? 3. Yet we have a contradiction here , because the clubshaft is in forward bend , so the hands must have a net 'negative torque' .
How can we have point 2 and 3 happening at the same time? This is why I do not believe that the SMK MOF concept is wholly accurate to explain the kinetics of the golf swing.
DG
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Post by imperfectgolfer on Sept 16, 2020 9:51:54 GMT -5
Dr Mann Don't you have some doubts about SMK's MOF concept? For example: 1. The only force that can be applied to the club is via the hands. 2. If you regard the point about which the 'Net force ' is applied being the 'fulcrum point of the left wrist' then that means you are assuming that the MOF (caused by a component of that Net force within the swing plane) is somehow causing a positive torque on the club via the hands. What else is in contact with the club? 3. Yet we have a contradiction here , because the clubshaft is in forward bend , so the hands must have a net 'negative torque' . How can we have point 2 and 3 happening at the same time? This is why I do not believe that the SMK MOF concept is wholly accurate to explain the kinetics of the golf swing. DG If you do not believe in the MoF concept, then what force/torque do you believe is causing the club to catch up to the left arm between P6 => P7? I think that the MoF concept is the same as the D'Alembert principle from an explanatory perspective, but it is more sophisticated because it can operate in two different directions (clockwise between P4 => P5.5 and counterclockwise after P5.5) and it can be quantified if one knows where the club is positioned at every moment of the downswing. Jeff.
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Post by imperfectgolfer on Sept 16, 2020 10:02:30 GMT -5
Dr Mann Don't you have some doubts about SMK's MOF concept? For example: 1. The only force that can be applied to the club is via the hands. 2. If you regard the point about which the 'Net force ' is applied being the 'fulcrum point of the left wrist' then that means you are assuming that the MOF (caused by a component of that Net force within the swing plane) is somehow causing a positive torque on the club via the hands. What else is in contact with the club? 3. Yet we have a contradiction here , because the clubshaft is in forward bend , so the hands must have a net 'negative torque' .
How can we have point 2 and 3 happening at the same time? This is why I do not believe that the SMK MOF concept is wholly accurate to explain the kinetics of the golf swing. DG Regarding the bold-highlighted statements, I think that the left hand is still pulling the club along the hand arc path between P6 => P7 thereby generating a positive MoF. However, the peripheral clubshaft is traveling faster than the club handle so the overall net torque must be negative. If a golfer's left hand slows down more than usual between P6 => P7, then the MoF will be less and the overall net torque will be greater. If the golfer can keep the hands from slowing down between P6 => P7 so that the club handle can better keep up with the peripheral clubshaft, then the overall net torque should be less and the degree of forward bend of the clubshaft should be less. Jeff.
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Post by dubiousgolfer on Sept 16, 2020 11:29:53 GMT -5
Dr Mann
"If you do not believe in the MoF concept, then what force/torque do you believe is causing the club to catch up to the left arm between P6 => P7?"
I cannot prove what forces are responsible but my initial feeling is that the clubheads COM is being accelerated primarily via 'Linear forces' applied to the handle from P6-P7. The 'Net force' and a PP1 type force are mainly responsible and it is not due to angular acceleration by a 'Net force induced MOF'.
I agree that the left hand is applying a pull linear force from P6-P7 and that (with the help of PP1) is accelerating the clubhead (not via the SMK Net Force Induced MOF). It accelerates the clubs COM in a targetwards direction such that the hands cannot keep up and the peripheral end bypasses the hands as the shaft aligns with the left arm (some of which is due to shaft rebound effect) . This causes forward shaft bend and a passive reactionary 'net' negative torque in the hands.
The MOF in the inverse dynamics equations tallies with D'Alembert principle , but they are not equivalent to SMK's MOF concept in his intro kinetics video. The important difference being that when using 'Inverse Dynamics/D'Alembert' the COM is not accelerated but in SMK video , it is accelerated.
DG
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