科学美国人60秒 SSS 鞋带易结也易解（在线收听）

Shoelace Study Untangles a Knotty Problem 鞋带易结也易解

You’re strolling down the street or maybe hauling that load of laundry down a flight of stairs when all of a sudden. [sound fx] Your laces come undone. If you’ve ever pondered what precipitates this pedestrian wardrobe malfunction, you might want to tie your shoes and beat a path to the Proceedings of the Royal Society A.

你在街上散步,也或许是在搬一大堆的衣服,突然……!!你的鞋带松了!如果你从未想过这种行人衣柜出的故障，或许你会绑好鞋带，开辟一条路去《英国皇家学会学报》。

In that journal, researchers have trotted out data that show that a combination of whipping and stomping forces is what causes laces to unravel without warning.

在这本杂志上，研究人员已经分析了数据，这些数据显示，甩来甩去以及跺脚这些结合的因素会导致鞋带毫无警告的松动。

The investigators noted that shoelace knots frequently fail when people are walking. But not when they are, say, sitting on the edge of a table and swinging their legs. Laces also stay tight when marching in place with no forward motion.

调查人员注意到，当人们在行走的时候，鞋带结经常松动。但是当他们坐在桌子的边缘，左右摆动双腿的时候却不会呢!当没有向前运动的时候，鞋带是不会松动的。

That led the gumshoes to suspect that stepping and swinging somehow work together to foil footwear security. But how? To untangle this knotty problem, the researchers made a slo-mo video of a student running on a treadmill, thus recording the literal steps that lead to catastrophic knot failure.

这导致行业们怀疑，踏步以及摇摆会阻止鞋子的安全性。但是是怎样的呢?为了解开这个棘手的问题，研究人员做了一个慢动作的视频，视频是关于学生在跑步机上跑步，因为这就记录了导致打结失败的一步步。

Here’s what they slowly saw: When the foot strikes the ground, the force of that impact causes the knot at the center of the lace to deform and stretch. And when the foot swings forward, the ends of the shoelace fly forward. That whipping motion pulls the knot open a bit more, which allows the free end of the lace to slip through a tiny bit. With each cycle of impact and whip, the free end slides a little more, until enough of it has come through that the knot finally unravels.

这是他们所慢慢看到的：当脚着地的时候，这种冲击力会使得鞋带结中心的变形、拉伸。当脚步向前的时候，鞋带也会向前飞。这就甩动的动作会导致鞋带结被再打开一点，进而导致鞋自由的一端在滑耸动一点。伴随一次次的冲击以及甩动，自由的一端变得一点点松动，最终从打的结中滑落出来。

The researchers confirmed that some knots are stronger than others. The granny knot that most of us use on our shoes is fairly weak and prone to failure, perhaps because the knot winds up twisted when pulled tight. A square knot, on the other hand, held up well in the treadmill test. To get that knot to buckle, the researchers had to attach weights to the free end to aid in the tugging of those whipping tips.

研究人员证实,有些结比较坚固。我们大多数人在鞋子上打的松8字结相当薄弱,容易滑落。也许是因为当我们拉紧的时候，这个结变形。而另一方面，方结，在跑步机上的测试则结果良好。为了得到这个结扣，研究人员必须在鞋带自由端增加一定的质量。

The researchers did not determine whether different types of laces are more likely to produce ties that bind. So though this initial study has made great strides in our understanding of shoelace mechanics, we still have a long way to go before this research is all tied up.

研究人员不能决定是否不同类型的鞋带会造成这种捆绑的。尽管最初的研究，让我们在理解鞋带的机理上取得了巨大的进展，但是，在研究全部结束之前，我们还有很长的路要走。