IAmTheWalrus wrote:Ok, I have to chime in here because I'm worried this conversation is going to keep going around in circles, which, while entertaining for a time, is not productive.
A few points:
1) There is so much confirmation bias within the Advanced Technique forum that little will be gained by trying to classify vaulters as "PB vaulters" or "<insert model here>." Everyone has their own things they focus on when watching a vault. One person may see a vaulter takeoff inside and immediately assume that he is not a PB vaulter, another may see someone take off free, but bend his trail leg and likewise assume that he is not a PB vaulter. Gibilisco takes off inside and tucks his legs, but he was coached by Petrov. It all comes down to a concrete definition and intent of the vaulter...etc....suffice to say, you are unlikely to clarify things by classifying vaulters as PB or not PB. More likely, you will introcude arguments tangential to the main topic of the post...which I have already forgotten.
2) Science!!! There have been several instances of people trying to support their claims by invoking the righteous name of science in this forum, however, their scientific arguments are often incomplete or full of fallacies. It is difficult to try to describe the vault with a classical mechanical model, and I applaud anyone who tries (not sarcastic at all, I really do mean that). However as is always the case with mathematical models, one must invariably make assumptions or hold certain values constant. In the case of the vault this is especially dangerous, since so many aspects are indeed variable.
Let's take for instance the case of the straight leg swing vs. the tuck. We all know the anecdote of the figure-skater who tucks her leg in to increase angular velocity. Quite often this is assumed to be the same for the vault, and while the same laws of physics apply (obviously) the situation is different, because angular momentum, angular velocity, and the moment of inertia are all variable. In the case of the figure skater the angular momentum is a constant (save for friction), so when she shortens the radius (changes her moment of inertia) her angular velocity MUST increase. With the vaulter this is not the case, which brings me to my 3rd and hopefully final point.
3) We can't forget about the actions of the vaulter. The vaulter is not freely hanging from the pole like the mass on the pendulum shown above, he has several opportunities to add a torque to the system. What makes the situation more interesting is the vaulters physical limitations. a rudimentary understanding of human physiology and biomechanics will tell you that there are limits to the amount of force that can be produced with a particular movement, limits to the speed at which the movement can be produced, and differences in both of these factors depending on the configuration of the vaulters limbs throughout the movement.
My response to why the straight leg swing may be beneficial is as follows: A vaulter (or some vaulters perhaps) cannot increase their swing speed enough by tucking to overcome the change in the vaulter's moment of inertia, resulting in a net loss in angular kinetic energy.
This is a theory, which I have not tested, but I think it is a good theory, based in the mathematics of classical physics which makes the case for the straight legged swing. My point is not to argue for any technical model, only to illustrate how science can be used to support a differing view.
I hope this alternative perspective can help us to move on in our discussion. I will now return to being an observer of this interesting discussion.
Note: I apologize for use of the gender specific pronouns used in this post. The same principles apply for female vaulters and male figure-skaters
1) My contention is that post take off because of the great diversity in body shape and ability the ideal form explodes in that diversity.
2) I have at once applied models and also talked quite a bit about their limitations. It is in fact a critique of the established models. We often simplify things. I have called it akin to linearization. One indeed has to know these limitations.
3) This discussion has in some respects turned into one of morphology diversity as regards to any model.
b) This may be true. And its also compounded by the angular relation of the CoM in the gravity field and its angular displacement and the deceleration of the CoM to PE gain. From the simple pendulum model it doesn't look good to have the CoM out displaced from the top hand in the horizontal. You are losing compressive force on the pole AND having gravity slow the swing rate even more. It's a very very complicated problem. RL seems to keep trying to slow the CoMs horizontal displacement from the top hand and when and where he can reorienting back and under it as much as possible. Does it offset any potential loss in angular KE? I don't know. Also, since energy can't really be lost, where does it go? My contention in part is it goes into the pole or can be directed into it. So manipulating the angular KE can effect the pole. And if energy is going into the pole it's going to bend more and have a shorter chord affecting the pole rotation speed. RL's approach is that he "balls up" under the top hand. Anyone that's been on a high bar understands it's easier from a dead position to "ball up" under their grip. It shortens the lever. Again, this doesn't refute your claim in the possible. It's just something to think about.
Much of this is about trying to divine if there are some boundary constraints based on size. One rarely sees long gymnasts based generally on the physics of longer rotating levers. But we have seen both shorter and taller vaulters where they may be able to satisfy the very necessary boundary state to complete the vault in different ways.
Feynman on Science http://www.lhup.edu/~DSIMANEK/cargocul.htm