There was a mystery that why shoelaces come untied. Now, the Mechanical Engineers at UC Berkeley have found an answer to it. The answer is, a double whammy of stomping and whipping forces acts like an invisible hand. It then looses the knot and drags on the free ends of your laces until the whole thing unravels.
It is essential to properly understand the mechanism of knots for sharper insight into how knotted structures fail under a variety of forces. In this study, scientists used a slow-motion camera and number of experiments to show that shoelace knot failure happens in a matter of seconds. It can be triggered by a complex interaction of forces.
Study co-author, Christopher Daily-Diamond said, “When you talk about knotted structures, if you can start to understand the shoelace, then you can apply it to other things, like DNA or microstructures, that fail under dynamic forces. This is the first step toward understanding why certain knots are better than others, which no one has really done.”
There are two ways to tie the common shoelace. One is based on square and stronger than the other. At the other hand, the weak version is based on a false knot that causes the knot to twist instead of lying flat when tightened. But, the problem is both ways fail in the same way.
Through this study, scientists want to develop a baseline mechanism of how shoelaces come untied under dynamic forces. They primarily record the process of a shoelace knot untying in slow motion. Then they laced up a pair of running shoes and ran on a treadmill while her colleagues filmed her shoes.
They found that your foot strikes the ground at seven times the force of gravity while running. This stretches knot and relaxes in response to that force. As the knot loosens, the swinging leg applies an inertial force on the free ends of the laces. This causes failure of the knot in as few as two strides after inertia acts on the laces.
Scientists also found a large magnitude of acceleration at the base of the knot. To find out more, scientists used an impacting pendulum to swing a shoelace knot. Through this, they tested knot mechanics using a variety of laces.
Gregg, a Berkeley Chancellor’s Fellow said, “Some laces might be better than others for tying knots, but the fundamental mechanics causing them to fail is the same, we believe.”
When a person is walking or running, his shoelaces don’t always come untied. Tightly tied laces require more impact cycles and leg swinging to cause knot failure.
Still, more research is required to find all the variables in the process.
Gregg said, “The interesting thing about this mechanism is that your laces can be fine for a really long time, and it’s not until you get one little bit of motion to cause loosening that starts this avalanche effect leading to knot failure.”