Around last week, I watched a ballet production at the Melbourne Arts Centre, and boy was I amazed! These people dressed up in costumes were spinning on their toes in all kinds of ways, and I was wondering how they did it; i.e. what were the physics behind it.
It's called a pirouette, I think, and I went here to learn more about it. The lady there says that males in particular can do up to ten pirouettes, and as the lady demonstrates, this is done on her toes. She also says that the number of turns one does depends on the skill of the dancer. This is not specific and does not give information on the physics behind the pirouette.
I know there must be centripetal force created. She said the arms open up, and as she turns, she closes them again, so this must be a drive for momentum. Her right leg is also turned outwards with her foot to her knee (some position called passe) so this might also cause momentum if she is pushing her knee back (which is what it looks like to me). Otherwise the lifted knee would send her leaning towards where it is, but when she turns, she is perfectly straight.
However, bringing the arms together and her foot on her knee concentrates a lot of force on just a small base area to work with; that is, the toes. Also, wouldn't torque be playing a role here?
If you get a rag and hold it from both ends, it will be pretty loose; but if you stretch it and try to move it, it will be tight and rigid. Maybe the ballet dancer is doing that to control torque? Pushing downwards and lifting upwards at the same time? Newton's third law?
Also, why does she start in fourth position for a pirouette? How does she know how much momentum to apply for one and two pirouettes? Why can males do ten?? That's crazy! Does this mean males are more skilled than females?
I think a key thing here is weight distribution. This would make a lot of sense, but I am not too sure.
What is the physics behind a pirouette?
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