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Researchers at the University of California, Berkeley have found that the gravitational pull experienced by shoelace knots as they unravel is greater than that experienced by rollercoaster riders. The team used accelerometers to measure the forces involved. They also found that the square knot was more effective than the granny knot, which failed 100% of the time.
It can be so annoying. You put on your running shoes, lace them up tightly and hit the road. In a short time, however, the ties have 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 his shoes to measure the gravitational pull 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 moved up and down were even greater than what a roller coaster rider would experience.
Suitable to be untied:
Using slow-motion video, the researchers observed two distinct phases of knot loosening: gradual slippage as unwinding begins, followed by total knot failure within the next two steps.
The research also demonstrated the superiority of the square knot, which failed about half the time, compared to the granny knot, which failed 100% 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.
