Very annoying and now - thanks to science - perfectly explained.
You know it: you are just nice and running and your lace is coming off. Just completely by itself. How is that possible? Researchers at the University of California Berkeley have broken their head and come across the magazine Proceedings of the Royal Society A with the redeeming answer.
Two things appear to play when your laces come off while you run. First of all, the lace is wobbled loose because your foot stomps on the ground a bit hard. In addition, the ends of the laces bump up as you walk around. And that also loosens the knot.
On the treadmill
The researchers base their conclusions on experiments. One of the researchers ran on a treadmill. Her shoes have since been filmed. The images reveal in detail how the laces come off. While the researchers were running, her foot hit the ground with a force seven times greater than gravity. Due to this force, the knot stretches out, to then 'relax' again. This gradually loosens. Meanwhile, the swinging movement of the legs also exerts a force (inertia) on the ends of the lace. And those two forces are therefore the basis for the loosening of a lace. They really have to play at the same time. "You can't get a failing lace without both forces," says researcher Christopher Daily-Diamond.
It may seem like a very playful investigation, but the opposite is true. “When you talk about knotted structures and you start to understand the shoelace, you can also let that knowledge go on other things, such as DNA and microstructures that fail under dynamic forces. This is the first step towards better understanding why certain nodes are better than others and that has actually never been investigated. "