# Torsional waves?

#### cmdr_sponge

has any one 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 realy hard about this but i cant 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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#### arcnets

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 [Broken]

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#### cmdr_sponge

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.

#### arcnets

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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