Re: Physics Based Critique of the Petrov Method
Posted: Fri Apr 04, 2014 9:24 am
Once again thank you to ADTF for correcting my error and for his kind offer to put up some critical stills from his video that will confirm
1. That Bubka was out at take-off and
2. Show “beyond reasonable doubt the distance “out” at take-off" was approximately half a metre.
(An approximate gauge that might be used is 1.5 to 2.0 of Lavillenie’s natural foot lengths on the photographic images. My guess estimate of foot length is in the 30 to 35 cms range based on Renaud’s stature. Someone may actually know his actual foot length).
Back to Willrieffer’s primary argument which is that the physics basis of the Petrov -Model Approach to teaching and coaching of flexible pole vaulting is in Will’s words:
“I contend that the Petrov model is full of hyperbole, half truths, and myths, in part because they got results! First of all is that Petrov and Bubka may have preached the "free take off" but Bubka did not practice it, at least as far as its described, in that if you simply look at the vids in vault after vault his pole starts bending about as soon as his take off foot hits the ground.”
Will’s claim that Bubka didn’t practice what he and Petrov preached is an untenable assertion.
Evidence can be presented to shows that Bubka performed during his career, in significant competitions on different occasions a pre-jump, free-take-offs and pre-pole bend take-offs. Applying pole vault jargon the jumps can be considered as “out”, “on” and “under” take-offs.
This demonstrates that Bubka’s performance varied with respect to the “on” rubric. This is but one of the criteria to be met in the performance of a “free take-off”.
A second and more important criterion of a free-take-off as defined (Petrov, 1985) is the extent to which the pole vaulter’s motion is resisted or impeded by the reactive forces on the vaulter induced by the pole striking the rear wall of the planting box.
A third criterion to be met in the performance of a Petrov-Bubka concept of a “Free-takeoff” is the extent to which the completion of the take-off enables the vaulter to achieve minimal resistance to penetration translatory motion due to vaulter take-off inertia whilst simultaneously allowing the vaulter to obtain the optimum swing amplitude and continously provide pole and vaulter rotation about pole tip and wrists.
A fourth criterion to be met in the execution of a free take-off is that the take-off ensures uninterrupted continuity of motion into active swing with minimal losses to the rate of pole chord rotation about the pole tip axis.
There is a fifth criterion that Petrov includes as necessary for a classification of a take-off to be considered “free” that relates to the manner in which the pole bend starts and is continued due to the interaction of the vaulter’s inertial force combining with the vaulter’s weight.
There are some other considerations but these 5 criteria I consider to be the essential ones in relation to just the take-off. The Petrov - Bubka Model is much more comprehensive and deals with the total pole vault sequence from gripping the pole, taking the first step to the culmination of the vault with the vaulter landing on the pads.
These criteria are essentially qualitative and rely upon the informed judgement of the external observer who is operating in an inertial frame of reference. (Is this what Will is asserting? If so I agree that qualitative criteria do not have the objectivity of physical law and principle!)
The vaulter on the other hand may be applying the same criteria with reference to a moving frame of reference and consequently their reports of what occurred during a particular vault may rely on perceived sensations that arrive from their effort and other sensory modalities. It is not surprising therefore that the vaulter’s account and that of the inertial frame observer can and do differ.
Will has yet to offer any clear physics analysis as to why he believes that taking off under creates more efficiency of energy transmission in the take-off.
Perhaps Will does not believe this to be the case and I have not understood his position on the matter.
There is no denial that Bubka on many occasions did not meet all 5 criteria I have listed on every vault.
Each occasion it must be remembered presents the vaulter with a unique set of circumstances, especially when vaulting under non ideal conditions outdoors. Part of the art is therefore modifying and adapting technique to meet the challenges imposed by the changing circumstances under which each vault takes place.
However, it is a very long bow to draw to state that Petrov and Bubka did not did not practice what they preached!
ADTF makes this same point and suggests that discussants are talking past each other because of lack of clarity in regard to their personal interpretations of what Petrov / Bubka actually consider a ”free take-off”.
ADTF goes on to say:
“The free takeoff is a flow or continuation of movements not a position or moment in time. Its a series of events not a photo. It is the ability of the vaulter to move thru the full running and jumping action at takeoff while receiving minimal tension on their body posture by the pole as it begins the stressed sensation of the two fixed points (the box and the top hand).”
I think the dynamic nature of the process of a “free take-off” is captured and functionally defined in ADTF’s statement rather neatly. I fully endorse this statement because it delivers the essence of what the free take-off contributes to a successful vault attempt.
I note Willrieffer has started another thread physics of pole vault Big Energy, perhaps there will be answers there.
1. That Bubka was out at take-off and
2. Show “beyond reasonable doubt the distance “out” at take-off" was approximately half a metre.
(An approximate gauge that might be used is 1.5 to 2.0 of Lavillenie’s natural foot lengths on the photographic images. My guess estimate of foot length is in the 30 to 35 cms range based on Renaud’s stature. Someone may actually know his actual foot length).
Back to Willrieffer’s primary argument which is that the physics basis of the Petrov -Model Approach to teaching and coaching of flexible pole vaulting is in Will’s words:
“I contend that the Petrov model is full of hyperbole, half truths, and myths, in part because they got results! First of all is that Petrov and Bubka may have preached the "free take off" but Bubka did not practice it, at least as far as its described, in that if you simply look at the vids in vault after vault his pole starts bending about as soon as his take off foot hits the ground.”
Will’s claim that Bubka didn’t practice what he and Petrov preached is an untenable assertion.
Evidence can be presented to shows that Bubka performed during his career, in significant competitions on different occasions a pre-jump, free-take-offs and pre-pole bend take-offs. Applying pole vault jargon the jumps can be considered as “out”, “on” and “under” take-offs.
This demonstrates that Bubka’s performance varied with respect to the “on” rubric. This is but one of the criteria to be met in the performance of a “free take-off”.
A second and more important criterion of a free-take-off as defined (Petrov, 1985) is the extent to which the pole vaulter’s motion is resisted or impeded by the reactive forces on the vaulter induced by the pole striking the rear wall of the planting box.
A third criterion to be met in the performance of a Petrov-Bubka concept of a “Free-takeoff” is the extent to which the completion of the take-off enables the vaulter to achieve minimal resistance to penetration translatory motion due to vaulter take-off inertia whilst simultaneously allowing the vaulter to obtain the optimum swing amplitude and continously provide pole and vaulter rotation about pole tip and wrists.
A fourth criterion to be met in the execution of a free take-off is that the take-off ensures uninterrupted continuity of motion into active swing with minimal losses to the rate of pole chord rotation about the pole tip axis.
There is a fifth criterion that Petrov includes as necessary for a classification of a take-off to be considered “free” that relates to the manner in which the pole bend starts and is continued due to the interaction of the vaulter’s inertial force combining with the vaulter’s weight.
There are some other considerations but these 5 criteria I consider to be the essential ones in relation to just the take-off. The Petrov - Bubka Model is much more comprehensive and deals with the total pole vault sequence from gripping the pole, taking the first step to the culmination of the vault with the vaulter landing on the pads.
These criteria are essentially qualitative and rely upon the informed judgement of the external observer who is operating in an inertial frame of reference. (Is this what Will is asserting? If so I agree that qualitative criteria do not have the objectivity of physical law and principle!)
The vaulter on the other hand may be applying the same criteria with reference to a moving frame of reference and consequently their reports of what occurred during a particular vault may rely on perceived sensations that arrive from their effort and other sensory modalities. It is not surprising therefore that the vaulter’s account and that of the inertial frame observer can and do differ.
Will has yet to offer any clear physics analysis as to why he believes that taking off under creates more efficiency of energy transmission in the take-off.
Perhaps Will does not believe this to be the case and I have not understood his position on the matter.
There is no denial that Bubka on many occasions did not meet all 5 criteria I have listed on every vault.
Each occasion it must be remembered presents the vaulter with a unique set of circumstances, especially when vaulting under non ideal conditions outdoors. Part of the art is therefore modifying and adapting technique to meet the challenges imposed by the changing circumstances under which each vault takes place.
However, it is a very long bow to draw to state that Petrov and Bubka did not did not practice what they preached!
ADTF makes this same point and suggests that discussants are talking past each other because of lack of clarity in regard to their personal interpretations of what Petrov / Bubka actually consider a ”free take-off”.
ADTF goes on to say:
“The free takeoff is a flow or continuation of movements not a position or moment in time. Its a series of events not a photo. It is the ability of the vaulter to move thru the full running and jumping action at takeoff while receiving minimal tension on their body posture by the pole as it begins the stressed sensation of the two fixed points (the box and the top hand).”
I think the dynamic nature of the process of a “free take-off” is captured and functionally defined in ADTF’s statement rather neatly. I fully endorse this statement because it delivers the essence of what the free take-off contributes to a successful vault attempt.
I note Willrieffer has started another thread physics of pole vault Big Energy, perhaps there will be answers there.