Linthorne Paper

[powerplant42]

Copy and paste the link minus the dashes.
--------http://people.brunel.ac.uk/~spstnpl/Publications/polevault(Linthorne).pdf--------

What is wrong in here?

[dj]

hey

thanks powerplant42.. i'll read my hard copy and hope to through out some thought...

two quick thoughts came to mind when i read the first few pages...

one… he said a lower or flatter takeoff angle is better with fiberglass. I don’t think there has been a “correct” explanation of how we determine that angle (how it is measured) or how it is actually created.

Number two he indicated that he did not agree with the premise that the shortening of the radius of the cord of the fiberglass pole had anything to do with the “benefit” of using fiberglass over steel..

Somewhere in this discussion I would like to “suggest” that any scientic discussion concerning the physics of the vault has to include and meet a “test” with these items receiving fair consideration.

One.. right off the top, the “amount” (percentage of bend based on grip) of pole bend.. should be included in all scientific work on pole vaulting.

Two.. the speed or time it takes to complete the whole vault from Takeoff to maximum height.. and this item can be broken into parts of: 1. time it takes to reach maximum bend, 2. maximum bend to inversion and 3. inversion to maximum height off the top.

To me these items need to be matched with the “picture” we see of every vault. In other words we term vaults the Petrov Model, the Tuck, the Tuck and Shoot Model, etc… we really don’t get the complete picture unless we know the “time x distance”… which will tell us if the vaulter delayed at one point and had to tuck (shorten the radius) just to catch back up with the pole, or if the amount of bend is important at all?

More later

dj

[powerplant42]

Some of the problem with it is that a lot of it is based on computer models that consist of God knows what...

[KirkB]

Some of the problem with it is that a lot of it is based on computer models that consist of God knows what...

What - you don't trust his assumptions re the Laws of Physics?

The main one that I question is the assumption that:

world-class male pole vaulters ... have a push height of about 1.00 m.

It's a stretch to assume that all elite vaulters have the same pushoff. He's just making this assumption to eliminate a variable that he can't pin down to any specific mathematical formula. But it does vary quite widely.

I think the rest are reasonable. You have to make SOME assumptions, or the formulae quickly become unwieldly.

Kirk

[KirkB]

... the speed or time it takes to complete the whole vault from Takeoff to maximum height.. and this item can be broken into parts of: 1. time it takes to reach maximum bend, 2. maximum bend to inversion and 3. inversion to maximum height off the top.

DJ, the issue of timing is a good point to raise.

As you may know - depending on how closely you read my Bryde Bend thread - I didn't catch this important issue back in my vaulting days. In 1971 (and the 2 years prior), I built my technique by self-discovery, day by day, and I tried to elaborate on it and enhance it to the extreme.

So much so that (without realizing it) I went past the "perfect balance" of how much to stretch into the Split position, how much to bend the pole, how early to invert, and how heavy of a pole to use. My premise was that if something was good, more of it would be even better.

It was only last October that I realilzed that later in 1971 - after the Pac-8 Meet - I was pausing too much in the Split (I now realize that ANY pause is already too much), and I was crushing the pole too much. By pausing in the Split, I wasn't following the "continuous chain" completely from top of runway thru to bar clearance.

Even last October (2008), when I came to my realization of these technical errors, I didn't quite understand why. Yes, pauses are BAD. But WHY? What's so important about the "Continuous Chain Theory"?

Today, after reading your post, I'm thinking that the answer is ... GRAVITY! Could that be it? It sounds almost too simple to be true! But maybe that's it!

I don't know how to explain this in physics terminology, but essentially, gravity is working AGAINST you from takeoff to bar clearance. (It then works FOR you, as you land in the pit.) So the less time you take on your way up, the less gravitational pull against your body. The force of gravity is approximately 9.8 meters per second squared. This defines the rate of acceleration of a mass (e.g. your body) in free fall towards the earth - after clearing the bar. BEFORE this, from the moment of takeoff to the moment of reaching your max CoM above the bar, gravity is working AGAINST you - at the rate of 9.8 m/s squared. However, you're hanging onto the pole, and fighting gravity thru your body manouvers (swing, extension, etc). This complicates the formula, but the physics principle is still there. As you're exerting UPWARDS force, gravity is exerting DOWNWARDS force.

Side bar: Interestingly, this force is identical for any weight of vaulter. Galileo proved this when he [reportedly] dropped a one-pound weight and a ten-pound weight from the Tower of Pisa, and they both hit the ground at the same time!

So ...

If you delay any part of your vault (e.g. pause in the Split), then you're giving gravity a chance to pull you down. But with the continuous chain in action, you're constantly moving on to the next vault part before gravity grabs ahold of you and drags you down. You're MINIMIZING the affect of gravity!

I'm trying to think of a good analogy for this. Maybe there's a better one, but what comes to mind is the skipping of a rock across a calm lake. The rock is heavier than the water, so if placed on the water's surface, you would expect it to sink. The water has some surface tension, so some things can float on it, even if they're heavier than the water. e.g. small leaves and insects. The rock is much heavier than a small leaf or insect, yet it can skip along the water without breaking thru its surface because you propel the rock at a fairly high speed. This speed is not only longitudinal, but also rotational. i.e. Like a spinning discus cutting aerodynamically thru the air, the spinning of the rock gives it even more resistance to sinking into the water. Eventually - depending on how well you threw it - the rock will slow down and sink into the water. That's when gravity finally wins out.

Perhaps the detail about the spinning of the rock isn't a necessary detail for this analogy to hold water? (big pun intended here!)

And maybe the detail about the surface tension of the water isn't necessary either?

I dunno, I'm just throwing it out here for greater minds to ponder. These two factors are simply additional factors (in addition to the horizontal speed of the rock) that work in favor of the rock staying "afloat", and AGAINST gravity.

The speed of your run/takeoff equates to the speed of the rock. If your speed at takeoff is too slow, you'll "sink". If you pause in the Split, you'll "sink". If your swing is too slow, you'll "sink". If you rock back and pause whilst the pole rolls to vertical, you'll "sink". If you extend passively (i.e. if you ride the pole), you'll "sink".

Maybe I'm the last one to figure this all out, and you all "got it" long ago?

Let me know if I'm on the right track, or if I'm "all wet". (another intentional hydro-pun!) Haha!

This question is not just for DJ - it's for anyone that has any thoughts about this.

Kirk