It’s a common issue: You tie your shoelaces, but before you know it, they’ve come undone. Why? Engineers at the University of California, Berkeley may have unraveled the mystery.
The researchers asked volunteers to tie their shoes, then walk or run on a treadmill. The team used high-speed cameras and motion sensors to observe how the shoelaces moved. They found that the force, or push, when a person’s foot strikes the ground gradually loosens the knot in a shoelace. And when the leg swings, it creates forces that tug at the lace’s ends.
A stronger knot can help shoelaces stay tied longer, says mechanical engineer Oliver O’Reilly. But “the combination of forces means that most knots will eventually come undone,” he says.