Bamboo/Steel versus Fiberglass/Carbon

[fx]

Say you are trying to teach a physics class about the pole vault. Naturally you would say that the fiberglass pole gives an advantage because it allows you to get on a longer pole, as the pole "shrinks" when you jump on it (the ends come closer together as it bends). However, you must also bring in the idea that fiberglass poles can store more energy than the wooden poles. How would you explain that the energy being put in through the run up and the jump is stored in the fiberglass pole, but lost in the wood or steel pole? Where does all this force go, if it is lost? Is is lost into the box?

[fx]

Just thought of another part to my question. Ususally softer poles will not shoot you as much or as high as the stiffer ones. Thus, more energy must be being conserved on the stiffer poles. Following this train of thought, I would think that steel or wooden poles, being perfectly stiff, would return energy perfectly.

[theczar]

Following this train of thought, I would think that steel or wooden poles, being perfectly stiff, would return energy perfectly.

you don't store energy in a wooden or steel pole, or not enough to do anything with anyway. The only thing that they would do is make you loose energy by absorbing alot of kenetic energy at the plant... and therefore you wont go as high.

So steel poles would not return energy perfectly, the only thing they are good for is absorbing kenetic energy.

[fx]

But where does this kinetic energy go? Is it actually absorbed by the pole? Also is the difference just about when the energy is returned? It seems like the fiberglass poles wait till you are deeper before it returns the energy, while maybe the stiff poles return energy as soon as you put it in?

[LHSpolevault]

Do the steel/wooden poles even return energy? Given that when you plant, they aren't manipulated to bend or move in any other way than to vertical. So even if they do return energy, it's entirely different from the energy return from a fiberglass/carbonfiber pole (energy is transferred as it unloads).

[theczar]

But where does this kinetic energy go? Is it actually absorbed by the pole? Also is the difference just about when the energy is returned? It seems like the fiberglass poles wait till you are deeper before it returns the energy, while maybe the stiff poles return energy as soon as you put it in?

the kenetic energy goes thru you, into the pole, into the plant box, and intot the ground and becomes absorbed.

[2-15-46]

Do the steel/wooden poles even return energy? Given that when you plant, they aren't manipulated to bend or move in any other way than to vertical. So even if they do return energy, it's entirely different from the energy return from a fiberglass/carbonfiber pole (energy is transferred as it unloads).

I grew up on a bamboo, steel pole, the Don "Tarzan" Bragg era,,,,, I jumped 13-6 in HS on one...... like Don and Dutch Wammerdam and all the the other WR holders of that era, the energy you great on the runway, is absorbed at the plant...the pole was a fulcrum and in order to get to verticle, you had to have speed and super strength to absorb the shock at the plant.... Wammerdamn had 9.7 hundred yard speed.... Bragg was fast , tall and a brute, Richards was fast and strong and a gymnastic guru......... I think Bubka would have ben a 16plus steel vaulter......fiberglass flexible poles allow you to hold higher... grab the stiffest pole you cannot bend and hold on to 13 foot and see what happens!!!!

[master]

Consider the following analogy where the beam relates to the box, the cable to the pole and the weight to the vaulter.

Situation 1) A steel cable is secured to an overhead beam. A solid weight is secured to the free end of the cable. The weight is held up so there is slack in the cable. This provides potential energy. The weight is then dropped (converting the potential energy into kinetic energy), the cable doesn't break and the weight bounces slightly and becomes stationary at the end of the cable. So what happens in this case is the weight is entirely rigid and therefore doesn't stretch and convert kinetic back to potential energy. The beam is very rigid and doesn't doesn't stretch and convert kinetic back to potential energy. The cable, although very strong likely stretched somewhat and converted most of the kinetic energy to potential and then returned it when it rebounded to its origianal length.

Situation 2) Now instead of a solid weight, an automotive innertube is filled with water and secured to the end of the cable. When this "weight" is dropped and it reaches the end of the cable, the inner tube is likely stretched and is what converts and returns almost all of the energy. (Hopefully it was a strong tube and didn't "pull a muscle".)

Situation 3) We keep the solid beam and the inner tube but replace the steel cable with a "bridge jumping" bungie. We drop the weight. The beam continues it's role. The bungie resists the inner tube but yields and stretches. The bungie is strong enough that it doesn't yield without a fight and the inner tube stretches in response. When each of these two elements stretch, they are converting kinetic energy back into potential energy. This is at a maximum when the bungie and the inner tube are at their maximum stretch.

A person can imagine each of these components having a degree of variability. The box (the beam) could be mounted in concrete or it could be a sliding box. The pole (the cable) could be made of steel or fiberglass. Our bodies (the weight) have some range of ability to stretch and rebound without damage, but this is minimal. However, how and when we move our bodies does impact the effective "flexibility" and efficiency of this compenent. Depending on the combination, each component will convert various amounts of the kinetic energy of the run.

Another important part of the discussion is the efficiency of the flexible parts of the system. If these are perfect components, no energy is lost. But they aren't. (If this were possible you could create a perpetual motion machine.) The lost energy is usually given up as heat from internal friction or external (with the air) friction. Modern poles I believe are very efficient, meaning most of what you put in you get back out. Using it efficiently (transferring the run kinetic energy into bending the pole and being positioned to use that energy when it unbends) is what makes vaulting a competitive sport.

- master

PS I modified this post, removing the word absorb and replacing it with what I think to be a more correct description.

[vaultwest]

Master, that was an instructional and fun analogy.

But also we must all remember that the majority of the energy in the vault is about rotating the pole/vaulter system from the plant position to the verticle.

The same basic physics rule whether you are using a straight/stiff pole or a bent/flexible pole. Where the energy hopefully mostly goes is in rotating this system to the verticle.

The bent pole shortens the radius of rotation thus allowing the vaulter to effectively hold higher. If one looks at the push off heights (the distance from the top hand hold minus the box to the bar height) one finds that there really isn't that much difference between straight/stiff pole vaulting and bent/flexible pole vaulting.

Thus the benefit is mostly in higher hand holds with the flexible pole and the conservation or storing of energy by the bending pole and consequentioal shortening of the pole is where the true advantage comes from.

Vault On

[master]

The bent pole shortens the radius of rotation thus allowing the vaulter to effectively hold higher. If one looks at the push off heights (the distance from the top hand hold minus the box to the bar height) one finds that there really isn't that much difference between straight/stiff pole vaulting and bent/flexible pole vaulting.

Thus the benefit is mostly in higher hand holds with the flexible pole and the conservation or storing of energy by the bending pole and consequentioal shortening of the pole is where the true advantage comes from.

So true!

- master

[2-15-46]

Consider the following analogy where the beam relates to the box, the cable to the pole and the weight to the vaulter.

Situation 1) A steel cable is secured to an overhead beam. A solid weight is secured to the free end of the cable. The weight is held up so there is slack in the cable. This provides potential energy. The weight is then dropped (converting the potential energy into kinetic energy), the cable doesn't break and the weight bounces slightly and becomes stationary at the end of the cable. So what happens in this case is the weight is entirely rigid and therefore doesn't stretch and convert kinetic back to potential energy. The beam is very rigid and doesn't doesn't stretch and convert kinetic back to potential energy. The cable, although very strong likely stretched somewhat and converted most of the kinetic energy to potential and then returned it when it rebounded to its origianal length.

Situation 2) Now instead of a solid weight, an automotive innertube is filled with water and secured to the end of the cable. When this "weight" is dropped and it reaches the end of the cable, the inner tube is likely stretched and is what converts and returns almost all of the energy. (Hopefully it was a strong tube and didn't "pull a muscle".) ;)

Situation 3) We keep the solid beam and the inner tube but replace the steel cable with a "bridge jumping" bungie. We drop the weight. The beam continues it's role. The bungie resists the inner tube but yields and stretches. The bungie is strong enough that it doesn't yield without a fight and the inner tube stretches in response. When each of these two elements stretch, they are converting kinetic energy back into potential energy. This is at a maximum when the bungie and the inner tube are at their maximum stretch.

A person can imagine each of these components having a degree of variability. The box (the beam) could be mounted in concrete or it could be a sliding box. The pole (the cable) could be made of steel or fiberglass. Our bodies (the weight) have some range of ability to stretch and rebound without damage, but this is minimal. However, how and when we move our bodies does impact the effective "flexibility" and efficiency of this compenent. Depending on the combination, each component will convert various amounts of the kinetic energy of the run.

Another important part of the discussion is the efficiency of the flexible parts of the system. If these are perfect components, no energy is lost. But they aren't. (If this were possible you could create a perpetual motion machine.) The lost energy is usually given up as heat from internal friction or external (with the air) friction. Modern poles I believe are very efficient, meaning most of what you put in you get back out. Using it efficiently (transferring the run kinetic energy into bending the pole and being positioned to use that energy when it unbends) is what makes vaulting a competitive sport.

- master

PS I modified this post, removing the word absorb and replacing it with what I think to be a more correct description.

great way of putting it....

[achtungpv]

Thus the benefit is mostly in higher hand holds with the flexible pole and the conservation or storing of energy by the bending pole and consequentioal shortening of the pole is where the true advantage comes from.

Vault On

Agreed.

I believe it was the Track & Field OmniBook that quoted a study that the average push off of 18' vaulters was only 4" greater than the pushoff of the best steel pole vaulters. Poles don't "throw" you.