BERKELEY, CALIFORNIA — Researchers at UC Berkeley have solved the mystery of why shoelaces come undone when you run.
During running, the foot strikes the ground at seven times the force of gravity, according to a study published in the journal Proceedings of the Royal Society A. This causes the knot to stretch. As the knot loosens, the running legs apply an inertial force on the free ends of the laces. This leads to the unravelling of the knot.
“You really need both the impulsive force at the base of the knot and you need the pulling forces of the free ends and the loops. You can’t seem to get knot failure without both,” study co-author Christopher Daily-Diamond said in a press release.
The researchers think their findings about shoelace knots will help them to understand more complex knotted structures that fail under dynamic forces, such as DNA.
