Kuwait Times

Catastroph­ic failure: Why shoelaces come undone

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A mystery as old as laced shoes was unraveled yesterday by experiment­s that reveal how shoestring­s come undone when we are on the move. “The failure of the knot happens in a matter of seconds, often without warning, and is catastroph­ic,” scientists reported in the journal Proceeding­s of the Royal Society A. The researcher­s meant “catastroph­ic” in a technical sense of complete, or total collapse-once the loosening begins, there’s no stopping it.

But while the cost of a straggling shoelace is rarely higher than a scraped knee or the time it takes to bend down and retie a bow, sometimes the consequenc­es can be devastatin­g. Lacerelate­d accidents dot local media around the world: the van driver who killed a motorcycli­st when his shoestring-wound tight around the accelerato­r prevented him from lifting his foot off the gas; the boy whose leg got pulled into the gears of an escalator; the cyclist who went head-over-handlebars into traffic.

Millions of shoelaces surely come unfurled every day, and yet the mechanics of that process had never been thoroughly examined. To tackle the enigma, a trio of mechanical engineers at the University of California at Berkeley filmed a knot-on the shoe of a researcher running on a treadmill-coming undone in extreme slow motion. The images suggested a two-pronged attack on the knot’s integrity.

A double whammy

“When running, your foot strikes the ground at seven times the force of gravity,” stretching and relaxing the knot, said co-author Christine Gregg, a graduate student. And then-as the knot relaxes-the legs swings into motion, applying additional force. “A double whammy of stomping and whipping forces acts like an invisible hand, loosening the knot and then tugging on the free ends of your laces until the whole thing unravels,” the researcher­s explained in a statement.

Follow-up tests with a mechanical foot-andleg showed that some laces were better than others, but none were impervious to failure. Of the two most commonly used knots to tie shoes, one is “weak” and the other “strong,” the study found. The strong version is based on a square knot, which is more symmetrica­l, while the socalled “false” knot twists when tightened rather than lying flat. Both fail in the same way, but one takes longer than the other.

“We were able to show that the weak knot will always fail and the strong knot will fail at a certain time scale,” said Professor Oliver O-Reilly, whose lab conducted the experiment­s. “But we still do not understand why there’s a fundamenta­l mechanical difference,” he added, leaving another knotty mystery to be solved.—AFP

 ??  ?? MANILA: This file photo shows a member of the Smokey Mountain baseball team tying his shoelace during practice at the former dumpsite in Manila. —AFP
MANILA: This file photo shows a member of the Smokey Mountain baseball team tying his shoelace during practice at the former dumpsite in Manila. —AFP

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