The Physics of Gymnastics

Geoffrey Taucer

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Here's my second blog entry, and the first of a multi-part series about the physics of gymnastics!


In this article, I described several at-home physics experiments; let me know if my descriptions aren't clear, and I'll try to explain them better, or put together a quick sketch to illustrate them.
 
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KineticChris

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Being slightly picky.....

The sentence "The center of mass also acts as the central point around which all rotation occurs" should probably read "The center of mass also acts as the central point around which all rotation occurs when in free flight". You could infer that from previous sentences, but the sentence itself is not accurate.

Similarly "Angular momentum causes the object to rotate around its own CoM" is a bit misleading. Angular momentum is a property of something which is already rotating not the cause of the rotation, it is a force which causes it to rotate, and not always around its CoM. A gymnast performing giants is clearly not rotating round their CoM, neither is a gymnast on their hands mid handspring, but both have angular momentum.

Not big things, maybe, but things which if misunderstood can cause confusion further down the line.
 

JBS

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Awesome... looks like we have some physics freaks out there. If you have questions about the physics of gymnastics... ask them now in this thread!
 
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Geoffrey Taucer

Former Admin
Gold Membership
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Former Gymnast
Jan 21, 2007
4,338
Baltimore, MD
Country
USA
Being slightly picky.....

The sentence "The center of mass also acts as the central point around which all rotation occurs" should probably read "The center of mass also acts as the central point around which all rotation occurs when in free flight". You could infer that from previous sentences, but the sentence itself is not accurate.

Similarly "Angular momentum causes the object to rotate around its own CoM" is a bit misleading. Angular momentum is a property of something which is already rotating not the cause of the rotation, it is a force which causes it to rotate, and not always around its CoM. A gymnast performing giants is clearly not rotating round their CoM, neither is a gymnast on their hands mid handspring, but both have angular momentum.

Not big things, maybe, but things which if misunderstood can cause confusion further down the line.

You are completely correct -- I suppose I was leaving the reader to infer from context that I was referring to what happens while the athlete is airborne, but I didn't specify it.

But then, pretty much anything we could say about classical mechanics as applied to gymnastics would properly have such a long list of clarifications and caveats that if I mentioned them all, the resulting article would be as long as a college physics textbook, so I try to keep the explanations contextually relevant and reasonably succinct and accessible, even if it means omitting some nuance.

For example my next article will discuss conservation of momentum, and how once an athlete is off the ground*, their momentum is conserved**, and they cannot*** change it****.

*Actually, we're assuming that the athlete does not come in contact with a spotter, a piece of equipment, a spotting belt, or an extremely strong gust of wind, all of which could alter their momentum

**Actually, they are constantly losing momentum to air friction, but the effect is negligible in the context of gymnastics

***Actually, the athlete could could alter her momentum by means of expelling some manner of propellant which would push her in the opposite direction, such as if she was wearing rocket boots, or carrying a very powerful motorized fan*****

****Actually, there is a slight tidal effect caused by the fact that not all of her body is exactly the same distance from the Earth, but the effect is negligible in the context of gymnastics******

*****Actually, she could also expel a lungful of air, or she could fart, and the same principle would apply, but the effect would be negligible in the context of gymnastics

******Actually, the way this effects her rotation might change depending on which direction she's rotating relative to the axis of the earth's rotation, the solar system's rotation, and the galactic plane, but these effects would be many orders of magnitude smaller even than the other effects we've already dismissed as negligible*******

*******Actually, all of this is probabilistic rather than deterministic due to the principles of quantum uncertainty, but the odds of simultaneous occurrence of a sufficient number of quantum anomalies to be noticed are so low that on average you'd have to do gymnastics for considerably longer than the expected lifespan of the universe before you'd actually see it happen********

********Actually, while I'm reasonably confident in my grasp of classical mechanics, my understanding of relativity theory is informal, my understanding of quantum mechanics could very generously be described as surface-level, and my grasp of anything beyond that is nonexistent, so we're well past the point where I actually have any clue what I'm talking about, but I suspect an expert physicist could continue even further down this rabbit hole*********

*********.... etc