willrieffer wrote: The timing and rate of the swing angle and its necessary relation to the CoM and gravity vector and thus that vector's effect on the compression and chord shortening of the pole are crucial to the vault.
The more that the vaulter can delay the movement of the CoM forward, the more they can have the gravity vector resolve into the pole and not into swing momentum, the better the vault, that is, if they can do this and cover the pole. That is the trick.
The gravity force I'm talking about adds to the compression rate of the pole, based on the progression of the swing angle to the shortening the chord, and thus by shortening it adds to its rotational velocity.
There has been not one single reply that has addressed this directly in refutation. Not one.
Willrieffer, I THINK you make some good points here, but I'm not sure.
What exactly do you mean by "gravity vector
"? That EXACT term has zero
hits on google.
Unless your terminology is well-understood, your points are lost.
When googling "gravity vector
", Wikipedia points to "scalar-tensor-vector gravity
Googling "gravity vector
", also finds this scientific paper: http://www.hep.princeton.edu/~mcdonald/examples/vectorgravity.pdf
Which of these are you referring to? Or do you have a third definition, perhaps more specific to PV?
Thanks for any clarifications you can make about what you mean. If we can understand what you mean, then we can reply specifically to your point.
First, thank you for this engagement Kirk.http://en.wikipedia.org/wiki/Vector_fieldhttp://en.wikipedia.org/wiki/Vector_calculus
Main article: Vector field
A vector field is an assignment of a vector to each point in a subset of space. A vector field in the plane, for instance, can be visualized as a collection of arrows with a given magnitude and direction each attached to a point in the plane. Vector fields are often used to model, for example, the speed and direction of a moving fluid throughout space, or the strength and direction of some force, such as the magnetic or gravitational force, as it changes from point to point.
The gravity field is a vector field and it is by this we say that gravity has a vector. The gravity vector. In the vault we can generally say it points down. Since the vaulter rotates on the top hand you have a progression of the CoM around the point, and the gravity vector points down. If, for example, a vaulter is practicing on a high bar and they are not swinging, all of the force of gravity is through the CoM and then to the high bar. The bar is supporting all of the weight, or the acceleration of the gravity vector on the CoM and through the body to the bar. Now as the vaulter swings forward what happens is that you have to do a resolution of the gravity vector by analysis. The swing has energy, and one element that can slow the swing is the effect of gravity once the swing is past the vertical. This is what generally decelerates any swinging motion, say of a child swinging on a playground. The angle here really means something because as the vaulter swings forward in time the gravity vector has to be resolved into parts now since it has constant value g, and is now both decelerating the swing AND still pulling down on the vaulter. So as the vaulter swings forward from horizontal it does some of both. At first its still mostly on the pole, but as the vaulter is always swinging forward, it changes to more swing deceleration and less compression force. This is why the swing angle in time and rate are important. And the farther forward the CoM in time, the more gravity has to be resolved into deceleration and not into compression because the force of gravity does not change. But what changes is the vaulters relation to it. The deceleration moment of the swing has to be resolved first, it has to happen, and then whatever force is left is what acts on the pole. This is the scientific reasoning why one needs to "stay behind the pole". This also leads to why the double leg is an advantage and why one needs to consider extension of the lead arm.
Longer levers rotate slower. So anything the vaulter can do to lower the CoM then slows their swing. Think about this. Now over time they are losing less of the gravity vector force in time to swing deceleration. And since the force is constant where must it go? Into the pole, as energy and compression. It effects the compression rate. This shortens the chord faster in time and make the pole rotate faster and farther. Plus it puts more energy in the pole.http://en.wikipedia.org/wiki/File:Oscil ... ndulum.gif
Look at the pendulum gif. The "a" vector is in direct relation to the gravity vector field, and it changes over time(at the point that the pendulum is vertical "a" completely opposes the gravity vector). And the force on the pivot point varies in relation. This is the same reason why a kid on a swing will, if they are swinging fast enough, when they get high up on the swing will "fly away" from the chain tension and show that at that point there is no counter force on the pivot point, which is where the chain attaches to the frame. For the vaulter this means there is no longer any compressive force on the pole from gravity. It also leads to the idea that the shorter the lever the vaulter makes to speed through the late swing when the pole is near or entering decompression has an advantage. Or, the tuck has an advantage if done at the right time(most IMHO are too late with it).
So look at what Lavillenie does. He drops the lead leg and works the trail leg back which both lowers and moves the CoM back in time. Lowering it makes him rotate slower. He actively does things to slow the rotation instead of letting gravity slow the swing! He loses less energy of the swing momentum to gravity and necessarily puts more energy in the pole and thus over time at this point at a faster rate. It is here I will address the lead arm. One cannot compare two vaulters lead arm action. One needs only to think about what happens when any vaulter with a bent arm extends it. By simple and pure geometry the arm gets longer and effects the swing angle as it pushes the shoulder back, followed by the torso, hips, and then CoM. When the arm extends it is longer. It has to push the system back. It is effective of the CoM in time. It pushes it back. And since it is back in time we have the same effect I have outlined above. There is less of the gravity vector resolved into the slowing the swing, and more goes into the pole. Now since Lavillenie has done all of this to "stall" his swing, he now has to radically tuck to speed his mid vault and cover the pole. This again is conservation of energy in rotation, the tuck is faster. Plus its easier to muscularly speed the tuck to cover. It's the difference between tucking to roll up to a high bar and levering up. That levering is harder to do and slower.
I'll ask you Kirk. Do you think these ideas have been countered or argumentatively addressed in any way by anyone here? I don't think so. And so we have again the point to PVStudent which is that I disagree with nothing he's posted or said here. The pics, the take off angles, etc. In fact I've agreed with almost all of it. The force of gravity is down on the pole despite what the left arm is doing. Good. Very good in my book. And yet he still has not addressed my point which I have made again and again and again, repeatedly. It is by this that I call his work peripheral to my point, and so even if it has value, and it does, it remains in my mind a "boondoggle" on my argument. It's barely pertinent, if at all. And so people look at what he is saying and, well, continue to be unable to focus on what I am saying and miss the point and veer off into other things.
Please feel free to ask any other questions.
And thanks for your time and interest.