Re: Unravelling the mysteries of coiling ropes

On Oct 26, 12:14 am, Sam Wormley <sworml...@xxxxxxxxx> wrote:
Unravelling the mysteries of coiling ropes
http://physicsworld.com/cws/article/news/31564;jsessionid=F2B86CF9053...

If you carefully lower a rope onto the floor it will probably form a
neat coil. While most people wouldn't give this a second thought, an
international team of physicists has done a series of experiments and
numerical simulations to work out why. Their new insights into
coiling could shed light on the behaviour of an important class of
materials called "elastic ropes", which includes DNA molecules and
structural reinforcing rods in buildings (Phys. Rev. Lett. 99
154302).

Neil Ribe at the University of Paris-7 and colleagues in Iran and the
Netherlands used a reel powered by an electric motor to feed ordinary
rope or thread down through a hole and onto a glass or paper plate
below. The rate of descent and the distance between the reel and the
plate could be changed, allowing the team to study coiling over a
wide range of speeds and drop lengths. A second set of similar
experiments looked at the coiling of soft strands of spaghetti.

Ribe told physicsworld.com that the team is the first to perform
controlled lab experiments on coiling and their use of different
materials allowed them to build up a comprehensive understanding of
why some ropes coil and others don't.

According to Ribe, one surprise result is that the coiling always
occurred at several different "frequencies" for fixed values of the
feed rate and fall distance. These frequencies correspond to the
vibrational modes of the nearly vertical upper part of the falling
rope. They discovered that coiling occurs when any of these
frequencies matches the angular frequency at which bottom end of the
rope whirls into a coil.

What is a "frequency", and how does it differ from a frequency?

.

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