Torsional Waves: The Mystery of the Spinning Chain Sphere Explained

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Discussion Overview

The discussion revolves around the phenomenon observed when a chain is spun rapidly, resulting in the formation of an oval sphere with a tail. Participants explore the mechanics behind this effect, particularly focusing on the concept of nodes and the relationship between rotation frequency and wave amplitude. The scope includes theoretical considerations and comparisons to standing waves and catenary lines.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant notes that spinning a chain creates an oval sphere with a tail, suggesting that the transition point between the sphere and the tail may represent a node.
  • Another participant relates the phenomenon to standing waves on a string, indicating a potential connection to wave mechanics.
  • A different participant expresses confusion regarding the relationship between rotation frequency and amplitude, questioning whether linear quantities in circular motion might play a role.
  • One participant challenges the string model by pointing out the lack of elasticity in a chain, proposing that the catenary line concept could be applied to a rotating frame of reference to explain the observed effect.

Areas of Agreement / Disagreement

Participants do not reach a consensus, as there are multiple competing views regarding the applicability of standing wave theory and the relevance of the catenary line in this context. The discussion remains unresolved with differing interpretations of the phenomenon.

Contextual Notes

Participants mention various physical concepts such as standing waves, elasticity, and catenary lines, but there are limitations in the assumptions made and the mathematical relationships discussed. The exact nature of the node and its calculation remains unclear.

Who May Find This Useful

This discussion may be of interest to those studying wave mechanics, rotational dynamics, or anyone curious about the physical properties of chains and their behavior under rotation.

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
 
Last edited by a moderator:
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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