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# Ballerina Wrist Weights

Iridium bracelets for faster spins
 (+17) [vote for, against]

Some extra strength training is probably a necessary part of this Idea. I'm aware that small weights are already in use JUST for strength-training purposes.

In this Idea, we want the weights to look like part of the costume. Not clunky, that is. Bracelets are about the only thing that can work. Which means if they are to offer significant weight, while looking delicate, they must be made of the densest materials available. Those are osmium and iridium (but osmium is a metal that quickly reacts with oxygen to make osmium tetroxide, a gas that both smells bad and is toxic, so that's out -- while iridium is more chemically inert than platinum).

Anyway when a ballerina goes into a spin, she starts with her arms outspread. After starting, she pulls in her arms and the spin rate increases. In terms of Physics, there is a Law of Conservation of Angular Momentum. When her arms are outspread, the total amount of Angular Momentum is divided in different ways between her arms and the rest of her body. Her hands are physically moving fastest of all, due to making the largest circle in the same amount of time as her body makes a much smaller circle. Since Momentum is associated with speed, when the ballerina pulls her arms in, the only way the Total Momentum can stay the same is if the spin increases.

Well, Momentum also depends on the total amount of mass that is moving. A ballerina that loses her hands in some horrible accident can never spin as fast as before, because she has lost the mass of those hands. But a ballerina that dons boxing gloves that have been illegally loaded with lead shot is going to have a LOT of mass moving fast in that large circle. If she has the strength to pull those heavily weighted hands in, then her top spinning speed will go up considerably.

The iridium bracelets (iridium is just about twice as dense as lead) represent a compromise, to add enough weight for a significant spin-speed boost, while not visually detracting from the performance.

 — Vernon, May 25 2006

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 Thanks, the last paragraph was all that I needed.

Sounds knackering.[+]for the visual of a ballerina imitating Taz.
 — skinflaps, May 25 2006

Yet another good reason to mine asteroids.
 — Shz, May 25 2006

 Vernon? Is that you? Only five paragraphs? Can't possibly be you.

Ribbing aside, though, I like this. If she's strong enough to pull her arms in with the extra mass, it would work. It may help figure skaters as well, as a faster spin would allow more turns during a jump. Quadruple spins? How about quintuple or sextuple spins?
 — Freefall, May 25 2006

[Freefall], excellent suggestion!
 — Vernon, May 25 2006

 Would this not, to a large degree, require her to have the power to accelerate the additional mass up to something approaching her non-mass-accentuated speed? Is her level of strength not what prevented her from spinning faster without the bracelets?

(I assume there's possibly some non-linearity at work that could make the idea work as stated, but don't recall the specifics of the calculations. Awaits re-education...)
 — half, May 26 2006

 here it is [half]:

 if the spinning starts while the arms are spread, the increase of speed is easy to accomplish, being limited by the ballerina's total mass.

 The total mass only has a slight percentage increase, but her hands, which actually give the spinning-speed-increase effect when lowered, have a more significant percentage mass increase.

Basically, the arms-spread-spinning-speed would be slightly smaller, but its increase when arms lowered would be significantly greater.
 — sweet, May 26 2006

So even though the total initial energy input to the system (initial momentum) is the same she'll spin faster with the addition of the mass.
 — half, May 26 2006

[half], part of the reason I opened the main text with a sentence about some EXTRA strength-training was to ensure that the ballerina could get a normal or near-normal intial arms-spread spin. Because as you pointed out, the Physics of Conservation of Momentum is such that if she can't start a spin with more than the normal initial momentum, then she can't end up with a faster spin. For proof, just compare the arms-in situation, with and without the bracelets. Even if the spins are the same speed, the with-bracelets scenario involves more momentum, because of the extra moving mass. For this Idea to be most obviously effective, then, the ballerina needs to try to make her initial arms-out spin speed, with bracelets, as near as possible to the without-bracelets norm.
 — Vernon, May 26 2006

 How can I have missed this? I especially like the compassion for the handless ballerina, as well as the / ballerina that dons boxing gloves that have been illegally loaded with lead shot is going to have a LOT of mass moving fast in that large circle./ I was unaware that there were regulations on what ballerinas could load into their boxing gloves.

"Whachu got in those gloves missy?" "Nothing. Not even hands since the biting goat trouble".
 — bungston, Sep 16 2016

Throwing the weighted arms to control entry into the spin will also have an advantage so long as the strength is there. Hammer spin up would be an extreme example.
 — wjt, Sep 16 2016

You don't need exotic materials, just securely bracelet fifteen pound lead weights on semi-flexible foot-long lines. Add a string pull mechanism to pull them in. Male and stronger female dancers can use longer lines and heavier weights not limited to actual hammer-throw hammers. Bonus: Sufficiently heavy weights can be used to pull the dancer into the air a bit longer via momentum transfer, and as a modification to center of gravity.
 — Voice, Sep 19 2016

Yo-Yo dancers.
 — wjt, Sep 20 2016

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