Fiber Facts: The physics of knots... or, why your yarn gets tangled

My mother is a great seamstress and a very crafty lady, and I learned to sew things as a child as part of our crafting. (The first thing I remember making, probably at the age of 5 or so, was a stuffed Grover head made out of old bits of leather my mom had scavenged from someplace--just a round head with no body.) My mom had a saying in German: "Langes Fädchen, faules Mädchen." Loosely translated, this means "Long thread, lazy girl." I swear she said this every single time I attempted to sew something. This refers, of course, to my tendency to use a superlong piece of thread so I could avoid tying off, threading the needle, etc. as much as possible. The problem with a long thread, though, is that it gets tangled and knotted up easily and ends up being just as much a pain in the ass as having to thread another needle. We all know my mom was right--but now scientists have explained why.

Researchers are interested in knots primarily because they hope to understand similar processes at a molecular level--apparently your DNA can get tangled up just like your yarn. But their ideas can tell us something about why we sometimes spend so much time detangling yarn that seems to form knots all by itself.

In a recent issue of the Proceedings of the National Academy of Sciences, Dorian Rymer and Douglas Smith explain that two main factors determine the degree of "knottiness" in a string--agitation and string length. Rymer and Smith tested this theory by dropping a string in a box, rotating and tumbling the box, and then examining the string and the types of knots that were formed. Then, they classified several different types of spontaneous knots (shown below):

(Apparently scientists are interested in knots in part because they look pretty--check out the images on The KnotPlot Site, for instance. )

The authors conclude the longer the string, and the more it is agitated, the more knots you will get. After a certain length, though, the knottiness factor levels off. The scientists also determined that it is the action of the free end of string that does the knotting, mostly by a kind of braiding motion that happens when the string is coiled (as in a skein of yarn, for instance). Unfortunately, they don't offer many tips for un-knotting string. Apparently modern science hasn't gotten that far yet. So the moral of the story is to keep your yarn short--just like my mom said.