"All Tied Up"
from The San Francisco Chronicle, April 14, 2017
Submitted by Kathy Powers
Christine Gregg, a recreational runner, had become curious about why her sneaker laces kept coming undone. So, for two years, she and fellow student Christopher Daily-Diamond photographed their shoelaces, videotaped their shoelaces, and got down on their hands and knees to study every last little thing about their shoelaces. They ran on treadmills and ran down the U.C. Berkeley hallways and tied and retied their shoes countless times.
"We spent hours and hours," she said.
Gregg found that shoelaces come undone because a shoe strikes the ground at seven times the force of gravity, stretching and relaxing the knot. The loosened knot is further undone when "the swinging leg applies and inertial force on the free ends of the laces," according to the research.
"The shoelace knot comes untied due to the same sort of motion-the inertial forces of the leg swinging back and forth while the knot is loosened from the shoe repeatedly hitting the ground." On a practical level, however, there was one key finding for all shoelace users. Gregg found that there is a strong shoelace knot and a weak shoelace knot. Many people tie the weak knot because they don't know any better.
To tie the strong knot, hold an end of the shoelace in each hand. Wrap the left end over the right end and pull it through. Make a loop with the right end, hold it in your right hand and wrap the left end around it counterclockwise, before pulling it through to finish the knot.
The resulting knot should align along the width of the shoe. That's a stronger knot, Gregg said, than one that aligns along the length of the shoe-the kind of knot that Gregg used to make before she did the study.
Professor Oliver O'Reilly, whose lab conducted the research, said he so sought nothing less than "understanding knots from a mechanical perspective." But even after two years, he said he did not understand why the clockwise-wrapped knot was stronger than the counterclockwise one.
"We still do not understand why there's a fundamental mechanical difference between those two knots," O'Reilly said.
The study was published in the journal of Proceedings of the Royal Society A of London alongside articles about airbags, tsunamis, and the Japanese art of paper folding. For a more definitive demonstration of the proper way to tie your shoelaces, go to Professor Shoelace, at https://www.youtube.com/watch?v=gVaS6TwzLc8.