PVstudent wrote:Will many thanks for your considered response to my last post. I have prepared some diagrams to try to clarify, for myself and possibly others, what you are meaning specifically when you discuss the changing role of gravity in relation to the action of the lower arm in particular that you believe is not considered in the PB methodology.
First, I DO think that the PB model is effective in this regard. They were highly interested in hip/CoM placement in the early vault and almost all of their methodology in that regards, their concern that the hips not be thrown forward by such effects as pole braking, work in this regard. They keep the hips back initially, re-align back while often "filling" with the left, and also work toward and carry a lot of radial energy in the take off foot and lower leg while also slowing the hips. Much of my ideas actually came from slo-mo viewings of Bubka!
PVstudent wrote:I still do not agree that I have taken liberties with the energy exchange graph. Nor do I accept your argument that there is not a differential increase in the total energy of the vaulter that can be attributed to vaulter's work in the pole bending and recoiling phases.
Ok. Let my try another tack. There are two types of high bar drills we might consider. Swing drills and Bubka's. Swing drills are relatively "flat" or are tied to the horizontal. Bubka's are tied to the vertical and are primarily concerned with "lifting" the vaulters CoM. For this specifically one needs something to pull/push on which in the case of a vault is the pole decompressing to vertical. Their relationship to potential energy are far different. One can enact a swing from a run onto the high bar passively. In fact I do this drill with my vaulters and so the vaulters swing again has elements of its energy come out of the effect of the take off effects, i.e. running momentum and pole braking, again something Petrov was keenly aware of in regard to our concerns here. We also know that some advocate for a more "passive" or natural swing while again we want to recognize Petrov's focus on it in the early swing and being "active" toward it.
The swing phase is very complicated, we know this. What is apparent however is that it has a tolerable window for the vaulter to hold their CoM in during the swings progress in time. If the vaulter "pushes" their CoM outside of this window, the vault fails. This happens all the time with beginning vaulters. They pull up on the pole early and as an example while this increases both their work they are doing and immediately increases their potential energy, it also stops a good vault from happening. Why? Because they have by work pushed their CoM out of the tolerable window set by the relation of the vaulters CoM, the pole, and gravity. Most notably in losing their relationship between gravity and the bending pole they have lost the resolution of the gravity vector into the pole compression rate. This happens as well when any vaulter take off "under" in the normal sense. Their swing CoM leaves the window for a good vault by being progressed which again puts the vaulter in a position where gravity adds less to pole compression while also draining more energy from the swing. Think about it. Think about a person on a normal backyard swing. The farther forward they swing, the more they slow down, and the more gravity is pulling them back toward earth. Of course this is the source of potential energy, but it is also everything a vaulter is fighting against! One of the other effects that can be seen in this common backyard swing system is "flying". The swinger "flies" when the forces of centripetal acceleration and gravity reach zero against their chains and they rebound into a moment of free fall. This only happens when the swinger slows near the top of the swing and when gravity is pulling perpendicular to their chains. If one "catches" a swinger only part way through their swing, they will not "fly" as gravity will still pull them down into the seat as well as along the chains. These are the effects I'm concerned with an I hope now you can see why. But these relations are terribly terribly complicated in a vault. The vaulter generates compression in the pole by means of several forces. Take off velocity and vector. Centripetal acceleration of the swing which is probably maximized when they cross the chord. And finally by the gravity vector being resolved and added to compression. And, while the vault is going on ALL of these values are changing! Its a mathematical nightmare involving a system of differential equations!
PVstudent wrote:Also I do not yet understand how an inanimate object such as a vaulting pole can be bent vastly beyond the range of deflection due to that induced by pole weight force and the moment it produces without an external agent producing that deflection increase. The external agent has got to be the vaulter! The other factors influencing the pole bend are trivial in comparison and on this we agree.
The agent IS the vaulter, but the force of gravity never ceases to act on the vaulter during the vault. Therefore it cannot be left out of any energy consideration including pole compression. Gravity does work, through the vaulter on pole compression and must be considered at all times in the energy relation. In the same way vaulting has changed from straight poles to flexible ones think of the difference between spring board diving and platform diving. IN both diving forms divers routinely do jumps and pre-jumps. If we consider the divers bodies as being equally capable of energy generation in both forms, we then consider the results where springboard divers are returned greater heights and far more potential energy capacity. Why? The flexible nature of the board with the effect of gravity grants greater acceleration through decompression! The pole vault is similar...and also different in that its much more complicated!
PVstudent wrote:Also how do you account for the kinetic energy decrease of the vaulter followed by the increase in kinetic energy? The energy has to have gone somewhere and some of it regained by the vaulter during initial pole recoil. The vaulter has more energy at pole release than at take-off. How do you account for this? How did the pole bend if not from the vaulter exchanging energy with it. The vaulter's weight obviously has a contribution as does his muscular useful work on the pole.
I think we will have to agree to disagree here and move on.
I don't think we have to disagree, although I'm not sure what is in contention! It's a complicated movement with varying rates of speed. The whole act of the vault is to redirect energy from the horizontal to the vertical. In this I find it no surprise that the vaulter first slows and then speeds up on a first compressing and then decompressing pole. The rates of all of these movements are very very important. A slight change in rate in pole compression or swing moment will doom a vault!
Vaulters do add to the energy. Have to. Must be so! A "Bubka" on a high bar radically alters a vaulters relation to gravity and thus potential energy.
PVstudent wrote: The simplification in the diagrams is deliberate and is done to try to be obvious. I am happy and aware that in this case I am taking liberties in regard to the actual complexity of the situation described.
You've looked at the diagrams right! Really, you are 100% correct and I still have humor tears in my eyes!
That's a lot of work, sir. A lot. Thank you. I know I did not address them specifically. Just there is ALWAYS a gravity vector addition to the vault. It has to be resolved with a vector diagram (which I must admit I have not done in....decades) into its pole compression (and decompression) element versus its swing slowing element...which is changing all the time!
Look, let me try and get to the basic idea I've put forth before. In looking at a lot of beginning vaulters enact bad vaults I just started to notice things based on my physics schooling. They usually go out of the CoM "window" by either going above it, i.e. they pull on the pole, or in front of it, i.e. taking of under and/or "hugging" the pole. Both things make them what I call "swing progressed" where gravity now is not adding at a high enough rate to pole compression while also draining at a faster rate from swing momentum. The vault is doomed. If that is the case, then should we not look at the opposite as being beneficial to the vault? That is would not advanced vaulters want to push the envelope toward the lowest and furthest back area of the window where they can still enact the vault? I think so. How is that accomplished? Well, they simply have to press back and down early on and try and retard the swing as much as possible while still enacting the vault. If you go back and watch the evolution of the vault you will see this effect take place! While not saying so specifically, the Petrovian's were aware of this relationship, and acted on it in their approach to the take off and early swing. Moving the take off back can and often does have a positive effect on this relationship. I watch Bubka and he is a master of reorienting back (a retardation of the CoMs forward motion that, yes, generates energy in the system and in the pole), keeping the hips quiet and smooth while all the while generating and carrying a high amount of radial energy in his take off foot and leg throughout the swing as is necessary if you are at all going to retard the CoM in the swing. These vaulters store more energy in the pole and swing extremities only to reclaim it later.
That's it. This is not old school american max pole bend OR free swing stuff. Its an orientation to gravity methodology that in fact owes a lot to Petrov's ideas and is in many ways I think, an extension of them, not in the particular, but in the general. It owes its generation to what causes bad vaults more than to what has seemed to create good ones, and a lot of thought experiments in physics. I hope that helps.