【经济学人】鞋带为什么会自己松开？ | 2017.04.15 | 总第876期

ENGINEERING brings great benefit to humanity, from aircraft to bicycles and from bridges to computer chips. It has, though, had difficulty creating a shoelace that does not accidentally come loose. At least in part, this is because no one has truly understood why shoelaces come undone in the first place. But that crucial gap in human knowledge has just been plugged. As they report in the Proceedings of the Royal Society, Christopher Daily-Diamond, Christine Gregg and Oliver O’Reilly, a group of engineers at the University of California, Berkeley, have now worked out the mechanics of shoelace-bow disintegration.

从飞机到自行车，从桥梁到电脑芯片，工程设计研究为人类带来了极大的便利。尽管如此，想要发明一种不会轻易松开的鞋带仍然存在困难。至少在某种程度上来说，这是因为没有人真正清楚为什么系紧的鞋带会自己松开。但如今，人类知识体系中的这一重大缺失已经补全。加州大学伯克利分校的三名工程师Christopher Daily-Diamond、Christine Gregg和Oliver O’Reilly在英国《皇家学会学报》上刊文称，他们已经弄清了鞋带蝴蝶结自然松脱的原理机制。

• Shoelace：n. 鞋带

• Bow：n. 弓；鞠躬；船首；蝴蝶结

A shoelace bow is a type of slip knot that has, at its core, a reef knot. Like conventional reef knots, bows can be mistied as “granny” knots, which come undone more easily than a true reef does. But even a shoelace bow with a true reef at its core will fail eventually, and have to be retied.

鞋带蝴蝶结是一种活结，其本质属于平结。与传统的平结类似，蝴蝶结很容易被误系成顺结，而顺结比真正的平结更容易松开。但是，就算使用真正的平结来系鞋带，最终的结果也会是鞋带松开，不得不重新系扎。

• Slip knot：活结；滑结

• Reef knot：平结；缩帆结

• Granny knot：顺结；十字结

Walking involves two mechanical processes, both of which might be expected to exert forces on a shoelace bow. One is the forward and back movement of the leg. The other is the impact of the shoe itself hitting the ground. Preliminary experiments carried out by Mr Daily-Diamond, Ms Gregg and Dr O’Reilly showed that neither of these alone is enough to persuade a bow to unravel. Both are needed. So they had to devise experiments which could measure and record what was going on while someone was actually walking.

人类的行走动作包含两个机械过程，而这二者都会对鞋带结造成影响。一个过程是腿部的前后运动，另一个是鞋子接触地面产生的冲击。Daily-Diamond先生、Gregg女士和O’Reilly博士开展的初步实验显示，这两个机械过程中的任何一个都不足以使鞋带结松脱，只有在二者同时作用下，鞋带结才会松开。所以，三名工程师设计了各种实验，对步行者的实际行走过程进行测量记录。

• Exert：vt. 运用，发挥；施以影响

• Preliminary：n. 准备；预赛；初步措施

• Devise：vt. 设计；想出；发明；图谋；遗赠

The “someone” in question was Ms Gregg, who endured numerous sessions on a treadmill so that the behaviour of her shoelaces could be monitored. Using cameras, and also tiny accelerometers attached to the laces, the researchers realised that two things are important. One is how the act of walking deforms the reef at the centre of a bow. The other is how the different inertial forces on the straight-ended and looped extremitiesof the bow conspire to pull the lace though the reef in the way a wearer would when taking a shoe off.

Gregg女士亲身上阵充当实验者。她在跑步机上进行了各种实验项目，并通过仪器监测自己鞋带的运动情况。借助摄像头和鞋带上的微型加速计，研究人员有两个重要发现：一是发现行走动作会使鞋带结中心的平结结构变形，二是鞋带结的绳花部分和蝴蝶结绳圈受到的惯性力不同，所以在两类末端的共同作用下，鞋带绳会被从平结结构中拉出，其机制类似于我们主动解开鞋带的动作。

• Treadmill：n. 踏车，跑步机

• Accelerometer：n. 加速计

• Inertial：adj. 惯性的；不活泼的

• Extremities：n. 四肢，骨端；末端，极限

• Conspire：vi. 共谋；协力

• Lace：n. 花边；鞋带；饰带；少量烈酒

The first thing which happens during walking is that the reef itself is loosened by the inertial forces of the lace ends pulling on it. This occurs as a walker’s foot moves first forward and then backward as it hits the ground during a stride. Immediately after that, the shock of impact distorts the reef still further. The combination of pull and distortion loosens the reef’s grip on the lace, permitting it to slip.

在人们行走时，鞋带结会由于鞋带末端惯性产生的拉力而自行松脱。这一情形发生在步行者迈步时，脚部先向前移动然后摆动至后方接触地面的过程中。此后，地面与脚部的冲击力随即使鞋带结进一步变形松散。在拉扯与形变的综合作用下，鞋带结最终无法保持紧绷，松脱开来。

• Stride：n. 大步；步幅；进展

In principle, the lace could slip either way, giving an equal chance of the bow eventually undoing completely or turning into a non-slip knot of the sort that long fingernails are needed to deal with. In practice, the former is far more common. The reason turns out to be that the free ends of the bow can swing farther than the looped ends do. The extra inertial force this causes favours slippage in the direction of the longer of the free ends. To start with, the effect is small. But as the free end in question continues to elongate, the disparity in inertial force gets bigger—and, eventually, only two or three strides are needed to take a shoe from being apparently securely tied to being untied.

原则上来说，鞋带会向两个方向滑动，所以鞋带结不仅有百分之五十的概率完全松脱，还有一半几率变成死结，让指甲不够长的人束手无策。而实际情况却是，鞋带结松脱的情况要远比系死结常见。其原因在于，鞋带绳花部分的摆动距离比蝴蝶结绳圈的摆动距离更长，所以这部分额外的惯性力使鞋带向绳花的方向滑动。起初，这一现象的效果并不明显。期待您的翻译，明天会有针对这句话的长难句解析哟~

• Elongate：vt. 拉长；使延长；使伸长

• Disparity：n. 不同；不一致；不等

Probably, nothing can be done about this differential elongation. But it might be possible to use the insights Mr Daily-Diamond, Ms Gregg and Dr O’Reilly have provided to create laces that restrict the distortion of the reef at a bow’s centre, and thus slow the whole process down. Regardless of any practical benefit, though, the three researchers, are surely contenders for an Ignobel prize. That award is made every year for work which “first makes you laugh, and then makes you think”. Their study of laces looks like a shoo-in.

这种鞋带伸长差异的发现对解决鞋带松脱问题可能没有什么帮助，但是三名工程师由此得到的见解却有助于制造新型鞋带，使鞋带结中心的平结结构不容易变形，从而减慢整个鞋带松脱的过程。且不论其实际意义，开展这项研究工作的三名科研人员肯定是搞笑诺贝尔奖的有力竞争者。每年一届的搞笑诺贝尔奖旨在评选出那些“乍看之下令人发笑，之后发人深省”的研究。而Daily-Diamond先生、Gregg女士和O’Reilly博士的这个鞋带研究课题无疑稳操胜券。

• Contender：n. 竞争者；争夺者

• Ignobel：搞笑诺贝尔奖

• Shoo-in：n. 长胜将军；十拿九稳的必胜者

翻译 ▍陌生、西柚、Serena

审核 ▍云图

图文编辑 ▍澜意

责任编辑丨毛毛