A cord of three strands…

Solomon said a cord of three strands isn’t easily broken, but these days we know much more about rope, including that one with three strands is always 68% the length of its component strands.

Despite rope’s obvious geometric properties, the art of rope making has been strangely neglected by mathematicians over the centuries. Today, Jakob Bohr and Kasper Olsen at the Technical University of Denmark put that right by proving the remarkable property that ropes cannot have more than a certain number of turns per unit length, a number which depends on the diameter of the component strands.