You just remember that this time they tied up and tightened the laces. But once again they after a while untie and irritatingly dangle with each movement. Why are the laces constantly untied? This question is so urgent that scientists decided to conduct a whole study, publishing its detailed results.
It turned out that during running or ordinary walking on the shoelaces there are much more forces than we assumed earlier. The study of the recordings of a high-speed camera that took off the occupation of a person on a treadmill showed that two forces are involved in untying the laces: the first occurs when the foot strikes the ground and evenly stretches the laces along their entire length, weakening the knot. At the same time, the overload with the impact of the foot on the ground during running was up to 7g. The second force is manifested by the movement of the foot, acting only on the ends of the lace, as if sipping them with an invisible hand.
Ultimately, the combination of the two forces leaves no chance for the usual knot, and after a while the laces are untied.