Chord Angle

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powerplant42
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Chord Angle

Unread postby powerplant42 » Sat Aug 29, 2009 4:43 pm

I have an interesting question...

When using the Petrov model, what is the ideal angle for the chord to be when the trail-leg passes it? Why?
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Re: Chord Angle

Unread postby baggettpv » Sat Aug 29, 2009 9:26 pm

45 degrees. First half is predominently forward the second half is predominently upward.

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Re: Chord Angle

Unread postby powerplant42 » Sat Aug 29, 2009 11:03 pm

Hmm. It just seemed to easy to me to say "45"...

How could we use chord angle (when the leg passes) as a video review tool?
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Re: Chord Angle

Unread postby baggettpv » Sun Aug 30, 2009 12:38 am

Back in the '80's I would position the camera on a tripod perpindicular to the takeoff. Upon replay of the tape on the TV screen I would tape an overhead sheet to the screen. Draw the runway, location of the box and a 45 degree line out from the box. Now I use IMovie on my Mac..... with a projector onto a white board.

When replaying the jumps you should ideally see the top hand, shoulders, hips and trail leg passing thru the 45 degree angle line at the same time. Ok, so now give us the reasons and quick solutions to these situations:
*Hips/Legs before the top hand
*Hips/Legs after the top hand

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Re: Chord Angle

Unread postby ADTF Academy » Sun Aug 30, 2009 1:32 pm

powerplant42 wrote: How could we use chord angle (when the leg passes) as a video review tool?


Call it what you want petrov or a swing based model.


Easy: Two Big ones that come to my mind quick.

1. Are you still long, meaning fulling extended body at this point are did you start to fold already ie foot leading butt sitting.

2. Position of trunk in relation to "45" to the box. Is the body behind this point, either staying back to long (locking out or staying on the bottom to long) on the plant or over excissive rowing of the hands towards the pits which would cause 1 to happen as well. Is the body infront at this point, mainly from taking off way under.

#2 shouldn't be an issue if your doing things correctly off the ground. The big one is #1 are you patient enough in the bottom of your swing to set up enough angular momentum to go upside down with ease or are you folding at the waist to acheive artifical rotational velocity with the foot which sadly causes the butt to sit in a chair.

I am sure there are more things you could fine tune look for but these would be the major ones that you can see with any equipment for replay.

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Re: Chord Angle

Unread postby Capt Caveman » Fri Sep 11, 2009 11:36 pm

The measure of a central angle is the same as the measure of the intercepted arc.
The measure of an inscribed angle is half the measure of the intercepted arc.
A segment connecting two points on a circle is called a chord.
A line passing through two points on a circle is called a secant.
A line external to a circle, passing through one point on the circle, is a tangent.

OR

chord1  /kɔrd/ Show Spelled Pronunciation [kawrd] Show IPA
Use chord in a Sentence
See web results for chord
See images of chord
–noun 1. a feeling or emotion: His story struck a chord of pity in the listeners.
2. Geometry. the line segment between two points on a given curve.
3. Engineering, Building Trades. a principal member of a truss extending from end to end, usually one of a pair of such members, more or less parallel and connected by a web composed of various compression and tension members.
4. Aeronautics. a straight line joining the trailing and leading edges of an airfoil section.
5. Anatomy. cord (def. 6)

With that in mind, is there such a thing as a chord "angle" or are you asking about chord LENGTH. Chord length would be based on grip height and how much your shorten, or bend, the pole. There is no angle in a chord? Or did I miss your point all together? What angle are you referring to at what point in the chord lengh of what, the pole or the athlete? There is a chord length of the athlete (tuck or long swing) or the chord length of the pole (grip height @ take off vs chord length @ max bend, distance from top hand to tip @ max bend).

I want to understand your question and possibly learn from it but baggetpv's reply of 45 degrees confuses me when I dont understand how a chord has an angle instead of a length.
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Re: Chord Angle

Unread postby master » Fri Sep 11, 2009 11:53 pm

Capt Caveman wrote:With that in mind, is there such a thing as a chord "angle" ...

I believe what is meant is: the angle the chord of the pole makes with the horizontal.
This is usually used when talking about the point in the vault when the vaulter's body passes the chord of the pole, and at that point, what is the angle the chord of the pole makes with the horizontal.

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Re: Chord Angle

Unread postby baggettpv » Sat Sep 12, 2009 12:14 am

a 45 degree angle between the runway and the chord of the pole (a straigth line between the top hand and the box). Geez guys just lay it out with some drafting tools on a piece of paper. Try goung to stabhocksprung.com and print out a sequence shot of the vaulters there. then put a 45 degree triangle to the pics and see what the relationships are.

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Re: Chord Angle

Unread postby Capt Caveman » Sat Sep 12, 2009 1:11 am

Thanks for the clairification. Since the "topic" was the chord angle, and there is no such thing, your answers make a lot more sense.

My follow up question would be - why is a 45 degree angle of the chord (straight line measurment from the tip to the top hand) optimum? If the pole speed is a variable to be considered could that angle not be greater for a big bender(grips high and bends the pole a lot - pole speed is low) or less for a vaulter that grips low (does not bend the pole much but but swings really fast and keeps the pole speed high, like Brian Mondschien - sp?)? How do you address the big bender vs the little bender with relation to the appropriate angle when the chord of the body passes the chord of the pole?
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Re: Chord Angle

Unread postby master » Sat Sep 12, 2009 1:32 am

Capt Caveman wrote:My follow up question would be - why is a 45 degree angle of the chord (straight line measurment from the tip to the top hand) optimum?

I believe this has been answered elsewhere in better detail than I will be able to provide, but I'll do what I can. I think this "measurement" of a good vault is more a characteristic rather than what you tell a vaulter to try to achieve. If you analyze enough vaults, you will likely find that if the vaulter passes the chord before it reaches 45 degrees that vault will most likely come up short of vertical. If the vaulter passes the chord after it reaches 45 degrees the vaulter will not have been able to successfully get inverted in time to clear the bar. Of course, there are various amounts of being off of 45 degrees. So for example, if a coach watches his vaulter pass the chord before it is at 45 degrees, it is a good indication the vaulter is hurrying his take off and swing. Having the vaulter adjust that will change the angle of the chord at the time the vaulter passes the chord and will likely improve the vaulter's jump.

That is what I understand the logic to be. There may likely be provable kinesthetic reasons for 45 degrees, but that is far beyond my knowledge.

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Re: Chord Angle

Unread postby baggettpv » Sat Sep 12, 2009 11:25 pm

Let's see how I can present this.
The top hand before the chord will be traveling mostly forward and some upward. At the 45 degree point the top hand will be traveling mor upward than forward. The point is that for a properly timed swing to handstand the body needs to go thru the same point of travel. The chord of the pole is the transition point from H>V to H+V to V>H
That help?

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Re: Chord Angle

Unread postby Capt Caveman » Mon Sep 14, 2009 3:13 pm

Yes Rick that does make more sense, thank you. It makes me wonder the next logical question in all of this. I go to my sons high school meets and hear one coach say "that kid needs to lower his grip" and another comment on the same jump "he could raise his grip". Since the chord lenth determines how much a pole is bent and the 45 degree angle you suggest is when the pole should start unbending - how much pole should there be with any given chord length? Lets use a 10 foot chord length as an example. If you measured a 10 foot chord length @ that 45 degree mark is there a grip height that you would expect to see based on that Chord? I am wrestling with how high is too high and how low is too low. I have read on this site bend being refferd to in "degrees" and in "percentages". I can grasp the % idea and how it relates to how high someone is gripping (and it makes sense with this topic). I am confused on how to measure the amount of angle a pole is bent and what is that angle related to? If the angle is just drawing a straight line through the bottom and top of the pole to form an angle (just my guess) and measuring that angle then I get it but I have tried using video to do this and it is difficult.

So 2 questions (one of them having 3 parts)
- how do you measure the "angle" a pole is bent to? what angle would you want to see if the chord is 10 feet? is there a way to determine grip height from this?
- what grip height would you expect to see if the chord length @ 45 degrees is 10 feet?

I hope this makes sense.
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