Knot physics: My Times Year in Ideas piece
A couple of weeks ago, the New York Times Magazine published its 2007 "Year in Ideas" issue -- their annual compendium of the year's most interesting and offbeat research. I wrote up five of their scientific and technological entries. The entire issue is online here for free, but I'm also archiving my pieces here for posterity's sake.
This one is about a pair of scientists that investigated the mystery of how laptop cords get tangled up so quickly when you leave them loose in your bag. Heh.
Knot Physics
When Doug Smith pulls the power cord for his laptop out of his bag, he inevitably finds that -- whoops! -- it has somehow tangled itself into a dense knot. This is, of course, a common complaint of the high-tech age (and before, with other types of cord). Most of us simply shrug. But Smith is a physics professor at the University of California, San Diego, and he wanted to know precisely why the knots form in the first place.
So he devised a clever experiment. Working with his research assistant Dorian Raymer, he took some string -- about the thickness of a computer-mouse cord -- and dropped it into a small square plastic box. They spun the box around for 10 seconds, then opened it up. Sure enough, they found “this really monster, complex knot,” Smith says. Then they repeated the experiment a dizzying 3,415 more times, using strings of different lengths and boxes of larger sizes, to see whether there were any rules that governed how badly the string knotted.
In the end, one law emerged: The longer the string, the more likely it is to form a knot. String that was 1.5 feet or shorter never got tangled up. But “as the string gets longer, the probability of a knot forming goes up and up,” Smith says, at least to 18 feet. Flexibility matters, too. The more pliable the string, the more likely it is to knot spontaneously.
Smith and Raymer then worked out the physical principles that explain why the knots form. When they programmed a computer model with these rules, it produced knots that predicted the results they got from the real-world box. In October they published their results in Proceedings of the National Academy of Sciences with a title worthy of Wallace Stevens: “Spontaneous knotting of an agitated string."
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I used to do electrical work for theaters and while I was always diligent about properly coiling my cables, I always wondered how cables so easily tangled themselves up with such little effort. I wonder what effect the strand makeup of the cord has on its propensity to knot. Most cords are made up of multiple strands twisted in various ways around each other, so is it really this factor that affects knotting, as the flexibility of the cords are largely determined by the strand makeup and twist?
Posted by: Trotsky's Ghost at January 10, 2008 3:48 PM
The first team of people to reverse-engineer this research and use it to create headphone cords which are less likely to tangle will end up very rich indeed.
Posted by: Tony at January 11, 2008 9:52 AM
Ghost, yeah, I've heard the same thing from roadies on rock-band tours. The cables are like their living nightmare. That's an awesome question about the stranded-ness of the cords ... the study I wrote about recorded the flexibility of the cords they used, so one could presumably figure out if it applies to the type of cords one uses in theater. And their finding was, as you'd expect, that the more flexible the cord, the more knots you get.
Tony, good lord yes!
Posted by: Clive at January 14, 2008 3:02 PM
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I used to do electrical work for theaters and while I was always diligent about properly coiling my cables, I always wondered how cables so easily tangled themselves up with such little effort. I wonder what effect the strand makeup of the cord has on its propensity to knot. Most cords are made up of multiple strands twisted in various ways around each other, so is it really this factor that affects knotting, as the flexibility of the cords are largely determined by the strand makeup and twist?
Posted by: Trotsky's Ghost![[TypeKey Profile Page]](http://www.collisiondetection.net/nav-commenters.gif)
at January 10, 2008 3:48 PM
The first team of people to reverse-engineer this research and use it to create headphone cords which are less likely to tangle will end up very rich indeed.
Posted by: Tony![[TypeKey Profile Page]](http://www.collisiondetection.net/nav-commenters.gif)
at January 11, 2008 9:52 AM
Ghost, yeah, I've heard the same thing from roadies on rock-band tours. The cables are like their living nightmare. That's an awesome question about the stranded-ness of the cords ... the study I wrote about recorded the flexibility of the cords they used, so one could presumably figure out if it applies to the type of cords one uses in theater. And their finding was, as you'd expect, that the more flexible the cord, the more knots you get.
Tony, good lord yes!
Posted by: Clive![[TypeKey Profile Page]](http://www.collisiondetection.net/nav-commenters.gif)
at January 14, 2008 3:02 PM