Why Do My Shoelaces Always Come Untied?

It can be so annoying. You slip on your running shoes, tie them tightly, and hit the road. Before long, though, the laces have come untied. Why does this always seem to happen? Oliver O’Reilly, a mechanical engineer at the University of California, Berkeley, also wanted to know. He and his research team put a test subject on a treadmill and attached accelerometers to her shoes to measure how much gravitational force the knot experienced with each step. The researchers found that as the knot began to unravel, the g-forces working against the knot as it bobbed up and down were even greater than what a rider on a roller coaster would experience.

Fit to be untied:

• Using slow-motion video, the researchers watched two distinct stages of knot loosening -- a gradual slippage when the unraveling begins, followed by total failure of the knot within the next two strides.
• The research also demonstrated the superiority of the square knot, which failed about half the time, over the granny knot, which failed 100 percent of the time.
• The findings were published in the April 2017 edition of the journal Proceedings of the Royal Society A — Mathematical, Physical & Engineering Sciences.