Wednesday, April 7, 2010

A New Theory of Rope

Sometimes it appears that that common phenomena are no longer mysterious and that all fundamental discoveries in physics can only occur deep in cosmic space or in high energy accelerator labs. But recently a pair of physicists from the Technical University of Denmark have come up with a new theory that explains rope.

Rope? What's to explain about rope? Rope seems to be made of helical coils like springs. But springs stretch and rope doesn't. What Jacob Bohr and Kasper Olsen have discovered are the mathematical conditions that must be satisfied so that rope doesn't stretch, conditions that had been discovered by trial and error centuries ago by ancient rope makers. Here's the abstract of Bohr and Olsen's paper "The Ancient Art of Laying Rope" as it appeared in today's physics arXiv.

We describe a hitherto overlooked 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 we show that it is a geometrical feature not a material property. This geometrical insight explains why nearly identical appearing rope can be made from very different materials and it is also the reason behind the unyielding nature of ropes. 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 rope.


Anonymous said...

Second Law of Mechanical (and Civil) Engineering: You can't push on a rope.

Anonymous said...

Published version can be found here: