Physics of the Vault: Big Energy

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Physics of the Vault: Big Energy

Unread postby willrieffer » Fri Apr 04, 2014 5:57 am


Heck, I have to take a breath to even start.

The vault is an exercise in energy manipulation, with two major sources. One is the vaulter, and the other is gravity. All other energy considerations are magnitudes different and while cannot be ignored in terms of the ideal vault also cannot take precedence over these two factors. Gravity, during the vault is more or less a constant, pulling down, and the end enemy in keeping the vaulter from height. Against this the vaulter has several means of impetus. Most notable is take off energy foremost as kinetic energy derived from their approach run where KE = mass times velocity squared. This is why any physicist would tell you that take off velocity is a, if not the, dominant factor in vault height theoretical, if not actual. Even small differences in take off velocity, as they are squared, make for big differences in energy potential for the vault.

Flexible poles, able to store energy, have made gravity less of an enemy, at least throughout the full vault. That is to say that during compression vaulters can orient themselves so that gravity is more of a friend and less of an enemy. They might "mine" energy from gravity in the early vault and then "escape" its clutches at a later point! And since gravity is such a large and constant factor in the vault, the vaulters constant relation to it is of paramount importance. This relation is neither obscured from most coaches, nor well understood.

Let's do some thought experiments.

Imagine a vaulter basically fully extended in their swing, parallel to the ground, rotating on their top hand, but at this point exerting no force on the pole. What is happening with gravity? Well, its full effect is in slowing the swing through the vaulters CoG. It is robbing the vaulter of energy. Now extrapolate back. As soon as the vaulter is progressed from the perpendicular this effect is taking place. And the further forward the vaulter is, the more energy that gravity is sapping from the swing. Ok. Think on that and lets think we might want to manage that relation...

Now imaging another situation. Imagine that the vaulter has just taken off, the pole is bending, and they are perpendicular to the ground and thus the gravity vector. In this situation gravity is not pulling any energy out of the swing at all! Also, its vector is being placed on the vaulter straight down, and in contrast to the pole, which is taking on energy as it resists the vaulters motion both forward AND down. These relations are why swing progression is a killer to the vault. It most often comes from being under where the torso generally takes off swing progressed, but can also come from "rowing" into a progressed torso, premature shortening of the rotational moment(pulling up the legs), or even throwing the head back. Also note that to let gravity alone control the swing moment is akin to giving up. The purely "free" swing is less then ideal.

In great vaulter after great vaulter one can see a re-orientation post take off from the C position. They work the pole forward and their hips and torso back in line with the top hand, in fact they retard the swing moment in the torso and hips. They do this with both arms and hands. They in fact do impart a "row" impetus down the pole axis, but are also not progressing the torso/closing the shoulder angle to the torso, but are working the torso hips back. It is a subtle but highly important difference. Most all of them also then initiate and carry a notable amount of their rotational momentum at the extreme of their rotation radius, that is the take off foot and lower leg. I would have to say that generally hip/torso swing moment has been stressed over lower leg rotation in many if not most, where the opposite should be the case.

The vault can be considered in the two phases of the pole. Compression, and Decompression. For the purposes of a vaulter and vaulting we need to add a third phase, transition. For this I will explain. For the Compression phase the vaulter wants to maximize the positive effects of gravity for as long as possible. They want to max the compression value of the gravity vector, while minimizing gravity pulling energy from the swing. This is necessarily behind the natural or "free" swing. For this they must slow the CoM. This action also moves the pole forward further for a good safe vault. Of course there is a catch. Too much action retarding the hips here will leave the hips stuck and end in a bailed vault. This makes the action of the hands necessarily complex. They need to re-orient, and yet not get caught and also not preform a "rowing" action that progresses the torso and hips forward. Also, the lower leg impetus and rotation cannot be ignored or minimized as the nature of rotational mechanics puts a paramount on radially distant action. Now, as the vaulter approaches transition, if they have retarded themselves from the natural swing, they need to progress through both the point of pole transition as well as past the parallel point where gravity will have the potential to rob the most energy from the swing. What do they do? As a figure skater does in generating a fast spin from a slow one by pulling in their arms and legs, most vaulters shorten there rotation axis in some way by pulling in the legs, more or less, and/or shortening the spine. I know the Petrov, in some instances, eschews this, but in practice most of the notable vaulters in that system, including Bubka, did not vault completely "straight legged". In particular I find that Tradenkov, one of, if not the slowest vaulter in that system, had to use more leg/rotational manipulation as to me, to keep up, he had to slow/elongate his early swing and to get out had to more or less "tuck". This idea finds its current end in Lavillenie who slows his early rotation by the addition of a quasi double leg swing and to get out has to effect a drastic "tuck" in transition to speed his rotation to get on top of the vault, all of which makes sense from a physics viewpoint.

This is also why ideal take off posture in most instances trumps the idealized take off point. That is, where ever the vaulter takes off, if they can get to the proper relation to gravity within a window of time, they will enact their swing pattern and vault. Advanced vaulters, masters, can more or less adjust to their actuality in take off over their idealized take off as whether they are in, out, pole bend, or free, they can initiate a posture and attitude to gravity that will enable a good vault. This of course, has limits with each and every vaulters. Beginning and novice vaulters have more problems as they have less experience in adjusting even if they have generally good take off posture. They will more often lean back, tilt the torso, ect, enter the vault "swing progressed", and will allow gravity to immediately and more effectively sap energy from their swing and escape addition to pole compression. They end up "yanked" up, have to bail, or end a vault dangerously short in or over the box.

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Re: Physics of the Vault: Big Energy

Unread postby vault3rb0y » Sun May 25, 2014 3:40 am

So what you're saying is that you have to finish your take off before you begin your inversion? Groundbreaking.
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