This is Why Shoelaces Unravel

Scientists have finally figured out what causes those pesky shoe strings to unfurl themselves so frequently.

Depending on the type of knot implemented, shoelaces will stay in place with varying amounts of success. The “square knot” is known to withstand the test of time better than the “granny knot.” Both are quite similar, but even the slightest distinctions make all the difference.

To determine why knots unravel, Oliver O’Reilly, a mechanical engineer at Berkeley, and his colleagues conducted a study. They had their test subject tie her shoes using a granny knot to increase the likelihood of it coming undone. Accelerometers were attached to her shoes to measure the g-force impacting the knot with every stride made while walking on a treadmill.

The team discovered two stages of knot slippage using slow-motion video. These were described as gradual loosening followed by catastrophic failure. It only took two strides to completely disband the knot after the initial loosening.

“We were able to see that these two combined effects lead to shoe knots failing,” O’Reilly says. “You need both together.”

A second experiment was conducted to determine the length of time it took for knots to unravel. Similar results were recorded that backed up the original findings of gradual loosening and catastrophic failure.

“If you could actually predict when a knot is going to fail,” he says, “that would have implications beyond shoelaces,” said Colin Adams, mathematician at Williams College in Williamstown, Massachusetts, who was not affiliated with the study.