This Is Why Your Shoelaces Come Untied
According to science.
BY Scott Christian | Apr 17, 2017 | Fashion
Life is nothing if not loaded with minor frustrations. Traffic, long lines at the supermarket, crappy Internet service. But perhaps none of those is more annoying than when a shoelace comes untied. It's like the paper cut of minor inconveniences. Small, but with an incongruous amount of (admittedly existential) pain.
Luckily, a group of mechanical engineers at the University of California, Berkeley have begun to unravel the mystery of why it happens. Beginning back in 2005, after a TED talk in which Terry Moore discussed how to properly tie shoes, the researchers wanted to understand why a knot failed at all.
They hypothesised a few different causes—that, among other things, the swinging leg causes the free strings to feel a force in the opposite direction, that the impact of the shoe hitting the ground causes the knot to deform, and that the repetition of those two makes the knot looser.
To test their hypotheses, the researchers built an experimental treadmill equipped with a super slow-mo 900 frame-per-second camera so that they could observe someone walking in a pair of those (woefully uncool) toe shoes. Using different knots and setups—some of which included a rope-driven pendulum attached to an accelerometer—they found that "catastrophic knot failure" was, in fact, due to the combination of the striking motion and swinging action.
The results, which were published yesterday in the journal Proceedings of the Royal Society Series A, also found that a "weak knot" always came untied before a "strong knot" (which seems fairly intuitive). If you're wondering what the difference is, you can re-watch Terry Moore's TED talk about it—but suffice it to say, if you tie your laces and they fall parallel to your foot, you've tied a weak knot, if they fall perpendicular, you've tied a strong knot.
Apart from tying a "strong knot," you can also just double-knot your laces, although that doesn't guarantee that they won't come untied. It just makes the knot a more complex problem to unravel.
Perhaps the most interesting thing about this research, though—beyond it helping us no longer feel like seven-year-olds who can't properly tie our shoes—is that physicists believe the findings could eventually help them understand how knotted structures like proteins and DNA untie themselves without breaking. In the meantime, no longer having to bend down on a crowded sidewalk to re-tie our laces is definitely a win.