What is the reason? Is it caused by their narrow shape, the soft material, walking vibration or something else?

  • $\begingroup$ I have to go, but I will leave you with this for now: In March 2009, a group at UCSD published a paper titled "Spontaneous knotting of an agitated string". It is under reference number 30 on Doug Smith's site (linked). Below the paper are links to newspaper articles that discuss it and surely provide a summary. There is also a paper titled "The Biophysics of Knotting" (reference #37), but that is about biophysical examples of knotting (DNA, umbilicus, etc.). $\endgroup$ – Mark C Nov 24 '10 at 0:24
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    $\begingroup$ I've always assumed it was down to entropy; Many more tangled configurations than untangled, but i don't know of any research done with string etc,but there is probably lots pertaining to things like proteins and nanotubes which is probably applicable. $\endgroup$ – reallygoodname Nov 24 '10 at 0:26
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    $\begingroup$ @reallygoodname: that only explains the result (i.e. reaching of thermodynamical equlibrium as dictated by second law) but tells you nothing about the dynamics of how the equilibrium is reached. In particular it doesn't tell you how much time it takes to reach it. It is perfectly possible that for some other materials the relaxation time could be something like few years and so they would effectively never tangle. And the relaxation time also obviously depends on how often you interact with the wires (so the mentioned walking vibration is surely quite relevant). $\endgroup$ – Marek Nov 24 '10 at 0:42
  • $\begingroup$ I think Sod's law explains this phenomenon pretty well! $\endgroup$ – Noldorin Nov 28 '10 at 19:28
  • $\begingroup$ Research into this topic won the 2008 (or was it 2009) IgNobel price in physics where it was quantified just how complex these nodes can get. $\endgroup$ – Lagerbaer Nov 28 '10 at 19:38

Because they are too long for the confined space. Reasoning: A very short string can't clot (say 1mm). So it needs a certain length before it can start clotting.

If they could be placed neatly (say big pocket), they wouldn't clot because the ends are too far apart.

They must be flexible. A steel bar doesn't clot.

So you need certain elements to be just right:

  1. Long enough
  2. Confined space
  3. Flexible
  4. Sticky surface (finger/skin oil, soft material, etc).
  5. Ends must be free to move

In the usual case, the string will be stuffed into the pocket without much consideration, so it will actually start somewhat clotted. If the ends aren't fixed somewhere, they will easily weave with the rest of the string. What makes matters worse is that the ends aren't thin. So you can't untangle everything by simple pulling.

The easiest way to avoid clotting is to fixate the two ends. In my case, I have a clip to pin the volume control to my clothes. If you fixate the two ends with that clip, they don't clot.

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