How ropes coil and knot

Two papers featured this week, both relating to behavior of macroscopic “soft” matter – namely ropes, threads, spaghetti and other linear elastic and flexible objects.

coiling.jpg

The first one is a PRL by Habibi et al., “Coiling of elastic ropes” Phys. Rev. Lett. 99, 154302 (2007).
If you drop a rope on the floor (also works for spaghetti), it tends to coil up. The authors investigate how this coiling comes about, what conditions lead to simple circular coiling, as opposed to figure 8 coling, etc.

dsmith.jpgThe second paper is a PNAS publication by Reymer and Smith “Spontaneous knotting of an agitated string” PNAS 104, 16432 (2007).

If you throw a long rope in a box and tuble it around (think about a rope in a dryer), it tends to tangle up in a knot. The authors did series of experiments for various lengths and types of ropes, analyzing resulting knots, in addition to complex mathematical simulations. It is a test of self-avoiding random walk theory, except applied to real objects with finite flexibility.

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