Shoe-String Theory: Engineers Unravel The Secrets Of Why Your Shoes Get Untied On Their Own


Time to solve the greatest and most annoying mystery of all time, why do our shoelaces untie on their own? Besides being a pain and sometimes an embarrassment, untied shoe laces can actually be pretty dangerous in case they trip you up.

The question was taken up by a group of mechanical engineers at the University of California, Berkeley, and they think the answer lies in a bunch of physical factors, unfortunately all going against us.

Originally the problem was identified by the engineers when they stumbled upon a 2005 TED talk by Terry Moore about how they can tie their shoes more effectively,

“It seems like no matter how hard you tie them they become untied,” graduate student and study co-author Christopher Daily-Diamond spoke. “That intrigued us. Why is it happening?”

The kept on working on the problem for years, and have come up with an interesting shoe-string theory. The team thinks that the knot opening comes mainly from the fore and after acceleration of the leg swinging, which makes the free strings undergo a force in the opposite direction leading to resistance against the knot and the consequential loosening. Adding to the woes is the impact of the shoes on the ground, which deforms the knot and decreases the hold of friction on the strings, making them slide out. The repetition of the impacting and deforming in combination with the swinging motion eventually gets the better of it. Also, the inertial force of the free string forces the loop side to get smaller and smaller, pushing through the knot until the whole knot unravels.

The researchers also verified this by using an experimental treadmill and filming a person in a pair of silly toe shoes, at super slow-mo 900 frames per second. The team also added a rope-driven pendulum to the accelerometer repeatedly banging it against the floor while also put on some weights to the aglets (end part of the shoelaces) to see when the knots fail. The findings have been published in the journal Proceedings of the Royal Society A today.

You can view the phenomenon of the untying shoes in the famous TED talk by Moore below, which also includes a way to ensure your laces don’t get themselves untied ever again.



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