Parents Number of springs in springboard

[Geoffrey Taucer]

I think you're right, but you need to keep in mind the the different acceleration/deceleration, which is going to be very apparent. When you jump on a spring with your full weight, the landing and take off is going to feel a lot softer if the spring compresses more -- this is due to spreading out the application of force over time.

In more formal language, the total amount of kinetic energy (your jump) that is converted into potential energy (a compressed spring) has nothing to do with the amount the spring is displaced -- a fat spring will store more energy for a given displacement than will a thing one. Even so, a stiffer spring is going to be much more jarring even of the total transfer of energy is the same.

Your point about not bottoming out is totally valid. That's a completely different sort of physics problem. The other issue, which I'm sure you know more about than me, to keep in mind is that springboards seem to kind of hop around a bit. That motion is going to cause a vaulter to loss a bit of kinetic energy through movement and friction. Probably negligible for a kid, but I bet you might see a different amount of movement given different spring counts.

The physics of gymnastics is interesting. If I had a second life career, I think I'd try to pursue coaching at a high level.

Ok, so writing as I think....

Our goal is threefold:
1) To maximize the kinetic power the athlete has when leaving the board
2) To optimize the trajectory of the athlete's center of mass when leaving the board
3) To optimize (not necessarily maximize, just optimize) the athlete's angular momentum when leaving the board.

Regarding the first one, some amount of power will always be lost into the floor, into the board's residual bounce after the athlete takes off, etc. My general sense is that this will probably be roughly the same regardless of how stiff or soft the board is, as long as it doesn't bottom out.

Regarding 2 and 3, if the board takes a longer time to compress and decompress, that results in a lower trajectory and more of the energy going into angular momentum rather than linear momentum -- but the athlete can also adjust for this with their angle on board contact, so we may be able to ignore this in the big picture.

So I THINK we can assume that any differences in exit trajectory and angular momentum can be accounted for by adjustments in entry technique, and just focus on maximizing kinetic energy on exiting the board. And I THINK we can assume that the general power loss remains the same regardless of how stiff or soft the board is, as long as it doesn't bottom out.

Which again leads me to thinking that the goal should be to make the board as soft as possible without bottoming out. But then that's leaning pretty heavily on the athlete (and coach) to optimize entry angle, which would probably change depending on the athlete's mass, run speed, and punching power.

 

[JPC13]

Which again leads me to thinking that the goal should be to make the board as soft as possible without bottoming out. But then that's leaning pretty heavily on the athlete (and coach) to optimize entry angle, which would probably change depending on the athlete's mass, run speed, and punching power.

I totally agree. Additionally, I think (at least for kids) that some might hold back on their punching power if they're expecting to hit a super hard board which just reinforces the "as soft as possible" POV. Then you factor in wear and tear on the body, and I think it's probably a no brainer.

From what I've seen, the heavier lower level girls seem to have an easier time on vault. I had always assumed it was just the extra "oomph" from jumping harder, but now I wonder if it's because more compression gives them more time to prepare for their body for preflight.

When my daughter vaults (a 47 pound 9 year old) it seems like a tenth of a second after she touches the vault she's in the air. Her 70 pound team mates seem to vault much much slower.

 

[Geoffrey Taucer]

Ok, so to sum up in practical terms (and again, if you think I'm off on any of this please do call me out):

1) The ideal number of springs for a given athlete is the lowest number that they can use WITHOUT flattening the board completely
2) It is up to the athlete and coach to figure out the ideal entry angle, which will be different for each athlete depending on their mass, run speed, etc.
3) Some amount of power will be lost to the floor, to residual board bounce, etc, but it's probably not worth the trouble of factoring that in when deciding the number of springs to use.

tl;dr: use the lowest-possible number of springs where the athlete won't cause the board to bottom out.

That all sound right?

 

[JPC13]

I think so.

 

[JBS]

@Geoffrey Taucer @JPC13 Got some questions for you both...

1. Hitting the board in different spots would change things right? For example... hitting the board at the very top vs the middle... or hitting in the corner vs the center. I would be getting different amounts of "X" from each spring depending on where the athlete hits the board?
2. Leading me to question 2. An athlete that does both forward entry and backward entry vaults may have different spring settings on each vault as the total force could be different based on where the athlete hits and how the board reacts. What I am getting at is the board a seems to react more like a diving board when you hit it on the very top (Yurchenko style). It reacts differently when hit in the center forward style. I have actually experimented with moving my most powerful Yurchenko vaulter down to the center of the board to get more "X" out of more springs. Is this logical thinking?
3. Sometimes at meets only the back of the vault runway is taped down. As the vault table slides away from the runway a gap is left between the runway and the table base. When the runway is setting on a slippery surface such as concrete... the runway will stretch when the board is hit. It will stretch quite a bit... maybe 3" or 4" on a powerful vaulter... this means the board is not only bouncing... but sliding. This is bad... right?

Anyways... love reading this conversation.

 

[CoachPow]

It’s been a long time since I took a dynamics class, but the force of a compressed spring is equal to K*X, where K is a constant dependent on the nature of the spring (thickness, material, etc) and X is the amount of displacement from resting.

Given that, from a force perspective I don’t think the number of springs would matter at all — assuming that you’re hitting them hard enough to displace them all.

What I think would be different is the deceleration on your body. You’d be much much more likely to hurt yourself vaulting on a board that barely moves than you would on one that displaces more. This is because your deceleration upon hitting the board would be much higher with less spring displacement.

The above assumes we’re talking about ideal springs, which we probably aren’t. The above expression only holds away from the extreme ends of compression (too little and too much). I don’t think I’ve ever seen an expression for a non ideal spring.

Given that, I think “just enough springs so you don’t get too close to bottoming out” is probably the right call. Just from an injury perspective, if nothing else.

The x is squared (I teach Physics as well as coach HS gymnastics) But I go with the almost bottom out the board theory. You can hear a distinctly different sound when a kid bottoms out the board. We will throw in the last spring for those, but it doesn't happen very often. Size of the gymnast is a general factor, but you will occasionally have a smaller kid who hits the board incredibly hard and bottoms it out. I agree with JBS above that it takes a significant amount of hand strength to swap springs, so unless I (or one other coach who does crossfit are at vault, the springs don't change, so the girls have to swap boards.

 

[CoachPow]

Ok, so just spitballing here, but

My understanding (and let me give a disclaimer that my education in mechanics is entirely informal) is that if an athlete puts in X amount of energy to compressing the springs, it doesn't really make a difference whether I'm slightly compressing a stiff springboard or significantly compressing a soft one, as they'll both put the same amount of power back out for a given amount of power put in, right?

But we're making some underlying assumptions here. First, we're assuming the springs don't bottom out; if they do, then any residual power goes into the floor under the board, and is (I suspect) dissipated rather than returned to the athlete. Second, we're assuming the athlete puts the same amount of power into a soft or stiff board.

I feel like an athlete is likely to punch more aggressively on a soft springboard than on a stiff springboard.

If I'm correct on all of this so far (and again, I'm just throwing ideas here and not claiming any real confidence in them), then the ideal solution would be to make the board as soft as possible (to encourage the athlete to punch as aggressively as possible) without bottoming out (which would dissipate excess energy into the floor).

@JPC13 does this sound right to you, or am I way off base?

The other thing to consider is the amount of distance the springboard has to recoil to launch the kid. More displacement distance means more time to fully rebound-which can influence their vault. Sort of like soft vs hard floor springs, or more springs on the tramp. On the other side, a harder board is tougher on their joints, so.......

 

[CoachPow]

@Geoffrey Taucer @JPC13 Got some questions for you both...

1. Hitting the board in different spots would change things right? For example... hitting the board at the very top vs the middle... or hitting in the corner vs the center. I would be getting different amounts of "X" from each spring depending on where the athlete hits the board?
2. Leading me to question 2. An athlete that does both forward entry and backward entry vaults may have different spring settings on each vault as the total force could be different based on where the athlete hits and how the board reacts. What I am getting at is the board a seems to react more like a diving board when you hit it on the very top (Yurchenko style). It reacts differently when hit in the center forward style. I have actually experimented with moving my most powerful Yurchenko vaulter down to the center of the board to get more "X" out of more springs. Is this logical thinking?
3. Sometimes at meets only the back of the vault runway is taped down. As the vault table slides away from the runway a gap is left between the runway and the table base. When the runway is setting on a slippery surface such as concrete... the runway will stretch when the board is hit. It will stretch quite a bit... maybe 3" or 4" on a powerful vaulter... this means the board is not only bouncing... but sliding. This is bad... right?

Anyways... love reading this conversation.

You hit a raw nerve with this one. I HATE when runways aren't properly taped down and you can see them slide and/or bunch up behind the board. We've got some powerful kids, and I've taken to bringing along mat tape and securing the runway during warm-ups (some probably see this as pretentious) so the runway doesn't move so much. If you're going to host a meet, spend the extra $12 on another roll of tape...

As to your other points, we always try to keep our girls on the center of the board. The way I see it, the rebound of the board itself and the positioning of the springs are designed to maximize the rebound from the curve, not the end of the board. I guess that's by observation, and not really from any formal direction. May be completely wrong.

 

[Geoffrey Taucer]

@Geoffrey Taucer @JPC13 Got some questions for you both...

1. Hitting the board in different spots would change things right? For example... hitting the board at the very top vs the middle... or hitting in the corner vs the center. I would be getting different amounts of "X" from each spring depending on where the athlete hits the board?
2. Leading me to question 2. An athlete that does both forward entry and backward entry vaults may have different spring settings on each vault as the total force could be different based on where the athlete hits and how the board reacts. What I am getting at is the board a seems to react more like a diving board when you hit it on the very top (Yurchenko style). It reacts differently when hit in the center forward style. I have actually experimented with moving my most powerful Yurchenko vaulter down to the center of the board to get more "X" out of more springs. Is this logical thinking?
3. Sometimes at meets only the back of the vault runway is taped down. As the vault table slides away from the runway a gap is left between the runway and the table base. When the runway is setting on a slippery surface such as concrete... the runway will stretch when the board is hit. It will stretch quite a bit... maybe 3" or 4" on a powerful vaulter... this means the board is not only bouncing... but sliding. This is bad... right?

Anyways... love reading this conversation.

First, let me once again reiterate the disclaimer that my expertise in the mechanics is informal and there are likely other people who can give a more reliably accurate and formal answer than I can. I'm just writing my thoughts as I picture it and think in through.

1) The ideal place to hit the board, it seems to me, would be the one where the force is spread as evenly as possible over all the springs. Or at least, that would be the case if all the springs were of equal length and started at equal compression, which they don't. The back row of springs is shorter, and even if the middle and front springs are the same length when taken out of the board, the middle row starts out more compressed and has less range of possible movement than the front row. The front of the board has much more room to compress and recoil than the middle or the back, so it's almost certainly better to hit further up than the middle row. But if you're too far forward, then you don't really get the benefit of the back and middle springs. I suspect figuring out the actual optimum spot would require us to factor in the elastic properties not only of the springs, but of the top part of the board, and I wouldn't begin to know how to do evaluate that. Or perhaps we can just treat the combined elasticity of the springs and the top of the board as a single variable?

My gut feeling is that the ideal spot would be roughly 2/3 to 3/4 of the way up the board.
EDIT: The more I think about it, the more I feel like 3/4 of the way up is too far forward. So 2/3 is where I'd aim.

2) As I see it, the biggest mechanical difference between a forward entry vault and a yurchenko entry is that in a forward entry vault, the athlete has no (or negligible) angular momentum as she contacts the board, and must generate all her rotation from the board; in a yurchenko entry, the athlete already has angular momentum when she arrives at the board. Which means that an athlete performing a yurchenko vault doesn't need to focus on generating nearly as much angular momentum with the punch, and should optimize much more for linear momentum. Which (I think) means that an athlete doing a yurchenko should hit the board at a lower angle... and might benefit from a slightly stiffer board, or from hitting farther back on the board than she would for a front entry vault?

I'd love to hear the other mechanists' thoughts on this.

3) Anything that allows the board to move (other than spring compression) when the athlete contacts it will likely result in a loss of power. In theory, the way to get the most powerful vault should be to bolt the board to the floor, but obviously that's not practical.

I suppose in theory if the vault runway stretches forward as the athlete first contacts the board, but then springs back into place before the athlete leaves the board, it could give the athlete additional angular momentum, but I doubt any vault runway will actually have the sort of elastic properties that would make that work in the real world.

 

[raenndrops]

Not one I'll claim any sort of confidence in. My gut intuition is that the ideal number of springs is whatever number results in the board almost-but-not-quite bottoming out when the athlete punches it, but I wouldn't be able to give any sort of detailed breakdown of why.

Lol, I was going to say the number of springs needed will leave the gymnast somewhere between NOT even engaging the springs and bottoming out.
Personally, I get a little kick out of a little "powerhouse" gymnast bottoming out the board with the same number of springs that bigger gymnasts use just fine (no bottoming out). In the 15 years I have been involved with team, I have seen 6 gymnasts with that type of power (mostly in Old L4/Current L3). Add another spring, add another 8-incher to the mat stack, and watch her fly!

In practice, we go by vault height. Coach does spring changes if needed, but the girls each move the hurdle line for the next one up.

 

[raenndrops]

Not one I'll claim any sort of confidence in. My gut intuition is that the ideal number of springs is whatever number results in the board almost-but-not-quite bottoming out when the athlete punches it, but I wouldn't be able to give any sort of detailed breakdown of why.

Bottoming out results in less momentum (physics word, lol). The springs are full of potential energy. When you jump on the springboard you are activating all of that energy and the kinetic energy propels the gymnast upward. If the gymnast is bottoming out the board, less kinetic energy can be expended on the rebound because some of it was absorbed by the body.

 

[cowfish36888]

it is so interesting. I do not know vault has to measure of the springs. My DD has the problem with vault score and I did not ask her about numbers of the springs. I will review with my DD.
Again, thanks for sharing.