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更新时间:2017-4-15 23:33:29 来源:纽约时报中文网 作者:佚名

Do Your Shoelaces Keep Coming Undone? Engineers Explain Why

Researchers at the University of California, Berkeley, have unraveled one of life’s enduring mysteries: Why do shoelaces come undone?


Forces at work


The researchers — Oliver M. O’Reilly, a professor of mechanical engineering, and Christine E. Gregg and Christopher A. Daily-Diamond, students who are pursuing a Ph.D. in mechanical engineering — reported that the force of your foot striking the ground and the motion of your leg combine to help loosen and ultimately untie the knot.

研究人员——机械工程教授奥利弗·M·奥莱利(Oliver M. O'Reilly),以及正在攻读博士学位的机械工程专业学生克莉丝汀·E·格里格(Christine E. Gregg)和克里斯托弗·A·戴利-戴蒙德(Christopher A. Daily-Diamond)——发布报告说,脚踩地面的力量,和你腿部的运动加在一起,导致了鞋带变松并最终解开。

When running, the foot hits the ground at about seven times the force of gravity. That impact is transmitted to the knot, which stretches and relaxes in response. As the knot loosens, swinging legs apply an inertial force on the free ends of the laces and — voilà! — pretty soon your laces are flopping around, looking like overcooked spaghetti.


Knots matter


The researchers identified “strong” knots, those commonly associated with square knots, and “weak” ones tied in the style of a “granny” knot.


For a quick way to know which is which, look at the loops of your laces. A weak knot will typically have one loop pointing toward the toes and one toward the ankle. A stronger knot typically has the loops oriented on opposite sides of each other, Mr. Daily-Diamond said.


For the shoelace-challenged, there are, of course, other options, such as loafers or sneakers with Velcro fasteners.


About the research


“We spent countless weekends walking up and down the hallways and staring at shoelaces, watching them coming apart,” Ms. Gregg said.


Initial experiments involved so-called barefoot running shoes, dress shoes, running sneakers and hiking boots.


Ms. Gregg said she spent hours sitting on a table, swinging her legs to see if the movement had any effect on the knot. It didn’t, and neither did merely stomping her feet.


Variables and unknowns


The force of her feet hitting the floor when she was walking or hitting the treadmill when she was running, combined with her gait, eventually caused the shoelaces to come undone. In an article published on Wednesday in The Proceedings of the Royal Society A, the researchers wrote that the unraveling was “a sudden and catastrophic phenomenon.”

在跑步时,她的双脚撞击地板或跑步机的力量,与步态相结合,最终导致了鞋带的松开。本周三在《英国皇家学报A》(Proceedings of the Royal Society A)上发表的一篇文章中,研究人员写道,这种松开是“突如其来的灾难性现象”。

The researchers used a high-speed camera to record Ms. Gregg running, and an accelerometer was attached to the knots to measure the forces on her feet.


Many variables, such as shoe and lace types as well as the tightness of the knot, were not assessed. “If you do a whole bunch of other variables, it just explodes,” Mr. O’Reilly said.


Coming up with the hypothesis and testing it took two years. Mr. O’Reilly added that the work was a “labor of love” that took place on nights and weekends after the researchers were done with their full-time jobs.


How does this research matter beyond the inconvenience of having to retie your laces? It has practical applications to things such as improving surgical sutures, he said.


Daughter inspired research


Mr. O’Reilly said the project began to germinate when he was teaching his daughter, Anna, now 14, how to tie her shoelaces when she was about five.


He said that for just about all of his 52 years, his laces have come undone. “I didn’t want her to inherit my problems,” said Mr. O’Reilly, who wears Converse sneakers.


So, after his extensive research, how have his laces been?


He said with a laugh: “It’s catastrophic. Every day.”