Magazine article Science News

Physicists Untangle Rope's Twists: Twine, String, Cord or Cable, It All Winds Up the Same Way

Magazine article Science News

Physicists Untangle Rope's Twists: Twine, String, Cord or Cable, It All Winds Up the Same Way

Article excerpt

Researchers have unraveled the math that keeps ropes from unwinding.

The trick lies in the number of times each strand in a rope is twisted, say Jakob Bohr and Kasper Olsen, physicists at the Technical University of Denmark in Lyngby. Their paper was posted online April 6 at arXiv.org.

In a traditional rope, each individual strand is twisted as much as possible in one direction. The twisted strands are then wound together in a spiral shape called a helix, which itself rotates in the opposite direction.

The interlocking of these twists and countertwists gives the rope strength so that when yanked, it does not unwind.

By plotting a rope's length against the number of times each strand is twisted, Bohr and Olsen discovered that there is a maximum number of twists--resulting in what is called the "zero-twist point" for the overall rope. A good rope--one that won't unravel when pulled or pushed--is always in the zero-twist configuration. …

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