Torsional Waves: The Mystery of the Spinning Chain Sphere Explained

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The discussion centers on the phenomenon observed when spinning a chain, which creates an oval shape with a tail. The key point is the relationship between the speed of rotation and the resulting shape, where a faster spin increases the horizontal radius of the sphere-like formation. Participants explore the concept of 'standing waves on a string' to explain this effect, noting that as the rotation frequency increases, the amplitude of the standing wave also increases, which differs from typical behavior seen in linear motion. The discussion also touches on the catenary line, suggesting that principles of minimum potential energy could apply to the rotating chain scenario. The challenge remains in accurately determining the 'node' where the sphere completes and the tail begins, indicating a need for further exploration of the physics involved in this phenomenon.
cmdr_sponge
has anyone ever noticed that if u hold a chain at one end and spin it round real fast u get a kind of oval shpere produced but with a tail at the end. the faster you spin the chain the greater the horizontal radius of the 'shpere'. i thought really hard about this but i can't work it out.

atm i think tht the point where the shpere is completed and the tail begins is some kind of node.

how can you explain this effect and work out where the 'node' will be produced?
 
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Hi cmdr_sponge,
I think the phenomenon you refer to, can be basically described as 'standing waves on a string'. Here's a nice site:

http://id.mind.net/~zona/mstm/physics/waves/standingWaves/standingWaves1/StandingWaves1.html
 
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i have studied standing waves. the only thing that confued me was that when the frequency of rotation increased the 'amplitude' of the standing wave increased, rather than when the amplitude of the driver is increased. i know that linear physical quanties (momentum etc) have related quantities in circular motion, could this have nething to do with it.
 
Maybe the 'string' model is not so good since a string has elasticity and a chain has not.
I had another idea. You know the 'catenary line'? It's the form a chain suspended at both ends, takes on. It has minimum potential energy and can be exactly calculated (it's basically ex + e-x).
Maybe if you apply this principle to a rotating frame of reference, you get what you want.
 

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