#leotardsanity explains

mybffnastia asked me to physics. So here are some physics I guess.

Okay, here's a fun fact about torque. It's... frustrating. I've always found it one of the most difficult concepts in physics, certainly in mechanics, and I've put a lot of what I knew about it aside as it's really not a thing in chemE.

Also, vault is really quite poorly suited to discussions without getting heavy on the biomechanics because, in spite of being the quickest event, physically it's one of the most complicated. Everything happens so quickly and is so cross-dependent that it's difficult to isolate anything after the takeoff for the board. The gymnast punches, drives her heels and blocks off the vault almost as one action, and the mechanics are as much dependent upon her shoulders and back or abs as they are the pure physics with the gymnast considered as a point body or simple object.

With that said, there are some decently simple isolations you can do that relate to angular momentum, the conservation thereof, and torque.

1) Entries. Straight entries (Yurchenko, handspring) are more powerful than twisting entries (Y 1/2 and full on, tsuk, hand full on). The twist of the entry robs angular momentum from the flip of the vault because the axes of these rotations are ideally at normal. Note that for accurate comparison you have to go by the direction of the block, not the direction on the springboard, as it affects the vault in an unrelated way- Yurchenkos, tsuks and Y 1/1s are considered back, handsprings, Y 1/2s and hand full ons are considered front. To simplify as much as possible I'd probably do FTY versus Y full on full off (FOFO? as both of these entries are still competed, whereas hand full on has kinda gone the way of Korbut.)

2) This concept can also be applied to the flight of the vault- you'd have to use men's as the example, but twisting double salto vaults are more difficult than twisting single salto vaults. This is not just due to having to fit an extra salto in, but also to the fact that the twist robs the salto of momentum and makes it more difficult to get around.

3) You can compare body positions- how the more vertically compact tuck makes flipping easier, but the more horizontally compact (relative to its other dimesions) layout makes twisting easier. This is related to the r in t=rxF BUT it's also got a lot to do with the gymnast's ability to generate force (F) which is related to this one and this gets way complicated and probably isn't the best for a 5 min presentation.

4) You can talk about how gymnasts control their twisting. Specifically, when a powerful gymnast does a vault that's easy for her, she will throw out her arms in a T or inverted V as her twist ends to slow it down. Observe on Kim Zmeskal's (STELLAR) FTY. This spreads out the gymnast's mass, which affects the moment of inertia in the rotation (essentially turning her from a point object to a rigid rotor if you consider only the two dimensions in which the rotation occurs.)

So you may remember my post from a few months back where I explained why some gymnasts maybe don't dance at the top of their abilities in competitions because of troubles with phasing and hearing the music in the arena. Now I'm going to talk about another thing that gets a lot of complaints: twisting form.

So a lot of female gymnasts go to do a laid-out twist and rather than looking like a log rolling through the air, well...

Pictured: A helicopter.

Why do some gymnasts do this? And why is it so much more common in WAG than MAG? A few months ago, someone (Vik?) made a post saying that it required more energy to hold the gymnast's body in the laid out position than to let it slop. While this is true, it's far from the biggest factor at work here.

Any object that is not perfectly spherical has what is known as a center of mass or center of gravity. Basically, if you throw the object or otherwise interact with it in a vacuum with no outside forces, the object will behave as if it is a sphere centered around the center of mass. Therefore, if you want to get something moving a certain way, the easiest way to do that is to get its center of mass moving that way.

Okay, that was the physics. Now for the anatomy. On a typical physically fit, full grown man, the center of gravity is generally located somewhere in the area of the breastbone (sternum) as a man's mass is concentrated mostly in his shoulders and chest. Therefore, to get his entire body twisting, all a man really has to do is roll his shoulders to the appropriate side, the tendency of his spine to remain attached to itself will do the rest.

With women, it's a bit more complicated. After puberty, a typical woman's mass is concentrated lower in her body, with her center of gravity near her navel. So to be able to twist quickly, she must start her hips rolling. The easiest way to do this is to just bring her leg over in the direction of her twist and use it to yank her hips around. Another method (try it laying on the floor or floating in the pool!) is to slightly pike the layout position and then open it up with a push to one side- and piked layouts are another common twisting form flaw in WAG. The faster the twist needs to be, the harder the gymnast must pull her weight around- and so these form errors are loads more common on skills with a large number of twists, such as the Amanar vault as compared to the DTY or 1.5TY, and the triple twisting laid out salto as compared to a 2.5 or smaller number of twists.