Why Your Shoelaces Untie Themselves?

Why Your Shoelaces Untie Themselves?

Isn't the worst feeling walking up the stairs or being in the middle of the game when you realize your shoelaces have came untied, only to trip on them seconds later? Well, scientists have looked for the meaning of this inevitability, and they have found it all has to do with physics. In their newest studies, researches at the University of California, Berkley determined the exact cause of our shoelaces becoming untied. Interestingly, "they found that the repeated impact of a shoe hitting the ground when we walk or run loosens the knot. Then, as we swing our legs, the whipping motion of the laces’ free ends pulls them apart. Within seconds, the knot untangles."

Also, these researchers said that shoelaces become untied quicker when a person is running. As the feet of a runner hit the ground harder, it makes the knot become stretched and relaxed. This impact from a runner hitting the ground is about 7 times the force of gravity. As the knot loosens, it can take up to about two more strides for the laces to completely untangle. 

The team of Berkley researchers teamed up with Christine Gregg and Christopher Daily-Diamond, a PhD students in mechanical engineering, and their professor Oliver O'Reilly. They figured it out by using physics and knowledge about materials and motion to design, develop, build and test devices. 

Their Tests
The team began by studying Gregg, who is a runner. They group watched her as she ran on the treadmill. "We noticed that nothing happened for a long time — and then the laces suddenly came untied," says Daily-Diamond. Again she repeated the process, but this time they videoed her shoes. They review the tape frame-by-frame. The team slowed down the action, which allowed them to watch the knot’s action in slow motion. They used a super-high-speed camera that takes 900 images, or frames, per second. Most video cameras record only about 30 frames per second. Our eyes don't see movement at 900 frames per second. We see in less detail. That's why it seems as if our shoelaces are firmly tied, and then suddenly aren't. "The researchers showed that both the stomping motion and the swinging ends of those laces are needed for a knot to untie. When Gregg sat on a chair and swung her legs back and forth, the knot stayed tied. The knot also stayed tied when she stomped on the ground without swinging her legs."


They also tested the best way to tie your shows. There are two common ways to tie shoelace. One is stronger than the other. 

The weaker bow is based on what’s called a granny knot. Here is how you do it: Cross the left end over the right end, then bring the left end under and out. Make a loop in your right hand. Wrap the other lace counter-clockwise around the loop before you pull it through.

A stronger bow is based on what’s called a square knot. It begins the same way — by crossing the left end over the right end, and bringing the left end under and out. But after making the loop in your right hand, you wrap the other lace clockwise around it.

Both types of bows will eventually come undone. But during a 15-minute running test, Gregg and her team showed that the weaker bow failed twice as often as the stronger one.



Other than just shoelaces this study can have a bigger impact of the science community. Study co-author Christopher Daily-Diamond explains in a statement: “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."

Sources

ChrobakApr. 11, 2017 , 7:15 PM, Ula. “Why Do Shoelaces Untie Themselves? This Team May Have the Answer.” Science , Science Magazine , 26 July 2017, www.sciencemag.org/news/2017/04/why-do-shoelaces-untie-themselves-team-may-have-answer.

 Oosthoek, Sharon. “Why Your Shoelaces Untie Themselves.” Science News for Students, Royal Society A, 21 July 2017, www.sciencenewsforstudents.org/article/why-your-shoelaces-untie-themselves. 

 Osborne, Hannah. “Your Shoelaces Are Doomed to Come Untied When You Walk.” Newsweek, Newsweek Media Group, 17 Apr. 2017, www.newsweek.com/shoelaces-untied-physics-582755. ]

Siegel, Ethan. “There's A Physics Trick To Keep Your Shoes From Coming Untied.” Forbes, Forbes Magazine, 13 Apr. 2017, www.forbes.com/sites/startswithabang/2017/04/13/theres-a-physics-trick-to-keep-your-shoes-from-coming-untied/#787add0b4830.

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