How shoelaces come undone

ENGINEERING brings great benefit to humanity, from aircraft to bicycles and from bridges to computer chips. It has, though, had difficulty creating a shoelace that does not accidentally come loose. At least in part, this is because no one has truly understood why shoelaces come undone in the first place. But that crucial gap in human knowledge has just been plugged. As they report in the Proceedings of the Royal Society, Christopher Daily-Diamond, Christine Gregg and Oliver O’Reilly, a group of engineers at the University of California, Berkeley, have now worked out the mechanics of shoelace-bow disintegration.

A shoelace bow is a type of slip knot that has, at its core, a reef knot. Like conventional reef knots, bows can be mistied as “granny” knots, which come undone more easily than a true reef does. But even a shoelace bow with a true reef at its core will fail eventually, and have to be retied.

Walking involves two mechanical processes, both of which might be expected to exert forces on a shoelace bow. One is the forward and back movement of the leg. The other is the impact of the shoe itself hitting the ground. Preliminary experiments carried out by Mr Daily-Diamond, Ms Gregg and Dr O’Reilly showed that neither of these alone is enough to persuade a bow to unravel. Both are needed. So they had to devise experiments…Continue reading
Source: Economist