Science & Technology

Scientists Just Discovered How Shoelaces Come Untied, and It's Weirder Than You'd Think

Science has uncovered some Earth-shattering mysteries, but that means that sometimes the everyday ones get lost in the shuffle. Shoelaces, for instance. Why do they come untied? Sure, you can make some safe assumptions as to why, but scientists had never put those assumptions to the test. Until 2017, that is, when a team of Berkeley mechanical engineers took slow-motion footage of shoelaces coming undone — and the results weren't what they expected.

The Rabbit Goes Around The Tree ...

According to Scientific American, when mechanical engineer Oliver O'Reilly was teaching his daughter to tie her shoes, he realized he didn't actually know why shoelaces come untied. When he tried to find the answer, he came up empty. Apparently nobody had ever studied the phenomenon before. O'Reilly looped a couple of Ph.D. students in on the mystery, and the three of them — O'Reilley, Christine E. Gregg, and Christopher A. Daily-Diamond — got to work.

But strangely, they didn't actually know how to make shoelaces come undone in the first place. As The New York Times reports, "Ms. Gregg said she spent hours sitting on a table, swinging her legs to see if the movement had any effect on the knot. It didn't, and neither did merely stomping her feet." Finally, running on a treadmill seemed to do the trick. The researchers aimed a slow-motion camera at the treadmill and placed an accelerometer on the shoes, one step closer to uncovering the mystery.

Watch Shoelaces Untie in Slow Motion

Real-World Data

The results? Contrary to what they expected, the knot didn't unravel slowly. As the researchers write in the 2017 study published in The Proceedings Of The Royal Society A, "the failure of the knot happens in a matter of seconds, often without warning, and is catastrophic." And as Gregg found earlier, it's not one thing, but many elements that cause that "catastrophic" failure: repeated impacts loosen the knot, while the repeated change in direction pulls out the laces. In all, these combined forces total 7gs, or roughly the force of an Apollo spacecraft on reentry, as Scientific American puts it.

If it sounds silly to put all this scientific brilliance into an inconvenience as minor as untied shoes, answer us this: How many things involve knots? Surgery stitches need them, high-speed network cables are challenged by them, and even computer animators can learn from them. When you understand how shoelace knots behave, you understand a lot more than just shoelaces. Simplicity can be deceiving.

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Learn more everyday physics in "Storm in a Teacup: The Physics of Everyday Life" by Helen Czerski. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Written by Ashley Hamer April 21, 2017

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