Friday, June 11, 2010

Making Rope

The ancient art of laying rope
We describe a geometrical property of helical structures and show how it accounts for the early art of ropemaking. Helices have a maximum number of rotations that can be added to them -- and it is shown that for an $N$-ply this is a geometrical feature, not a material property. This geometrical insight explains why nearly identically appearing ropes can be made from very different materials and it is also the reason behind the unyielding nature of ropes. The maximally rotated strands behave as zero-twist structures. Under strain they neither rotate one or the other way. The necessity for the rope to be stretched while being laid, known from Egyptian tomb scenes, follows straightforwardly, as does the function of the top, an old tool for laying ropes. The repetitive structures of twisted metal wires in Viking arm and neck rings are discussed in the light of the new insight arising for the understanding of zero-twist structures. They are maximally rotated structures.

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