MadSci Network: Other

Re: Why do strings tangle and get knots so easy?

Date: Fri Dec 23 04:48:42 2005
Posted By: David Akerman, Staff, R&D Scientist, Clear Edge
Area of science: Other
ID: 1134220986.Ot

Hi there,

The simple answer to your question is that there isn't a "tangling force" responsible for the knots and entanglement.

However, by putting things into the drawer and then opening and closing it you are helping to make the string tangle up. I think there are two reasons for this:

  1. The string is usually not smooth - you can see the ends of lots of fine fibres (or filaments) coming off the main length of the string and these mean that the string is "sticky". The filaments are there because the string is made from thousands of these all twisted together. Lots of twisted filaments are much stronger than one big, solid rod - this applies to every type of fibre, from the cotton in clothes to the metal ropes holding up suspension bridges.

    Anyway, the filaments work like small hooks and catch anything that comes into contact with them. This could be anything in the drawer with the string, or it could be other parts of the same string.

  2. Every time you open (or close) the drawer, you first pull (or push) the drawer and everything in the drawer comes with it, but before the drawer falls out you quickly stop it. This action makes the items in the drawer slide about, bang into each other and generally churns things up. This especially true of the string because it is very light and easily pushed around.
So, now you have a churning action and the sticky string all the time is pressed against lots of things and sticking to them or to itself.

To have a string that didn't knot you'd have to stop either the stickiness or the churning action (or both). Making the string smooth isn't really possible, so you'll have to stop the churning action by opening and closing the drawer much more carefully!

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