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up vote 34 down vote favorite
7

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

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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. – reallygoodname Nov 24 '10 at 0:26
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@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). – Marek Nov 24 '10 at 0:42
I think Sod's law explains this phenomenon pretty well! – Noldorin Nov 28 '10 at 19:28
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. – Lagerbaer Nov 28 '10 at 19:38
@Lagerbaer It was 2008. To be nitpicky, the paper is about string and not earphones with three ends. The paper was entitled "Spontaneous knotting of an agitated string": ncbi.nlm.nih.gov/sites/ppmc/articles/PMC2034230 – Russ Jan 5 '11 at 14:30

2 Answers

up vote 31 down vote accepted

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.).

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Any papers on how hairs manage to thread themselves through clothing? – endolith Nov 24 '10 at 1:21
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Thank you for these interesting articles. Now I notice that the three free ends play an important role in this specific example. – gerry Nov 24 '10 at 1:37
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Hairs have one-way movement (or a preffered direction at least) and therefore with agitation will move in that direction, even if it threads through clothing. Don't know if there's any papers on it though. – Dom Nov 24 '10 at 10:00
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physics.ucsd.edu/~des/AnnReviewKnots.pdf clickable link to #37 mentioned above. – Alex C Nov 24 '10 at 12:57
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It would be nice to give perhaps a short summary or idea of what is written in the referenced papers. That way we can decide whether or not to delve into that ourselves or not. Also it would improve the quality of answers in general. – Gerard Nov 24 '10 at 15:51
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up vote 8 down vote

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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