Shoestring theory

November 1, 2017
This article appeared in Berkeley Engineer magazine, Fall 2017

diagram of shoestring coming untiedWhy do shoelaces keep coming untied? It’s a question everyone asks, often after stopping to retie their shoes, yet one that nobody had investigated. Now, a study conducted in the lab of Oliver O’Reilly, professor of mechanical engineering, suggests the answer is that a double whammy of stomping and whipping forces acts like an invisible hand, loosening the knot and then tugging on the free ends of your laces until the whole thing unravels. The study is more than an example of science answering a seemingly obvious question. A better understanding of knot mechanics is needed for sharper insight into how knotted structures fail under a variety of forces. “When you talk about knotted structures, if you can start to understand the shoelace, then you can apply it to other things — like DNA or microstructures — that fail under dynamic forces,” says Christopher Daily-Diamond, who co-authored the study with fellow graduate student Christine Gregg. “This is the first step toward understanding why certain knots are better than others, which no one has really done.”