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Physicists have found out why laces are untied



Physicists using high-speed shooting found that the reason for untying the laces are the changing forces when moving the legs. The main role of the scientists was given to the forces of inertia, which are pulled by the free ends of the laces during accelerated movement of the foot, and the reaction to the impact of the foot against the surface. The study is published in the journal Proceedings of the Royal Society A. A summary is available on the EurekAlert website!
"If you deal with laces, you can say a lot about DNA and other systems that decay under the influence of dynamic forces ," says co-author Christopher Daley-Diamond from the University of California at Berkeley.
The aim of the research was to understand the mechanics of the process of unbinding the knot-band on laces under the influence of dynamic forces. Previous work described how nodes are unleashed under continuous loads, but little attention has been paid to dynamic changes in forces and loads. Scientists have found out that the force developed by impact against the surface is seven times greater than the force of gravity. The node is stretched and relaxed in response to the impact. Then, the ascending with the acceleration foot causes the forces of inertia pulling at the free ends, which can quickly untie the weakened knot.

In addition to the dynamic interaction of forces on the node, high-speed photography also showed a large amount of acceleration at the base of the node. "We need both an impulse force at the base of the assembly, and a pulling force at the free ends and loops," Daly-Diamond explains. "Apparently, the node does not untie itself without both components." The authors checked their conclusions by increasing the weight of the ends, and the knot began to untie much faster. 

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