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练习 | 科学美国人：鞋带为什么会松

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鞋带为什么会松？

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科学美国人60秒: 鞋带为什么会松

燕山大学刘立军宋崴编写

◆TRANSCRIPT

This is Scientific American - 60-Second Science. I'm Karen Hopkin. This will just take a minute.

You're strolling down the street or maybe hauling that load of laundry down a flight of stairs when all of a sudden. 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.

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.

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.

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.

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.

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 ends to aid in the tugging of those whipping tips.

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.

For Scientific American - 60-Second Science. I'm Karen Hopkin.

Adapted from 鞋带为什么会松

◆VOCABULARY

1. haul v. to pull sth./sb. with a lot of effort （用力）拖，拉，拽。例如：
○The wagons were hauled by horses. 那些货车是马拉的。
○He reached down and hauled Liz up onto the wall. 他俯身把利兹拉上墙头。

2. ponder v. ponder (about/on/over sth.) (formal) to think about sth. carefully for a period of time 沉思；考虑；琢磨

○She pondered over his words. 她反复琢磨他的话。
○They were left to ponder on the implications of the announcement. 他们被留下来琢磨这项宣告的含义。

○The senator pondered the question for a moment. 这位参议员考虑了一下这个问题。

○They are pondering whether the money could be better used elsewhere. 他们正在斟酌能否把钱花到其他更适当的地方。

3. precipitate v. to make sth., especially sth. bad, happen suddenly or sooner than it should 使…突然降临；加速（坏事的发生）。例如：His resignation precipitated a leadership crisis. 他的辞职立即引发了领导层的危机。

4. whipping n. an act of hitting sb. with a whip , as a punishment 鞭打，鞭笞（作为惩罚）

5. stomp v. (informal) to walk, dance, or move with heavy steps 迈着重重的步子走（或跳舞、移动）。例如：She stomped angrily out of the office. 她怒气冲冲，重步走出办公室。

6. unravel v. if you unravel threads that are twisted, woven or knitted, or if they unravel , they become separated （把缠或织在一起的线）解开，拆散，松开。例如：I unravelled the string and wound it into a ball. 我把绳子解开并绕成一个球。

◆QUESTIONS
Read the statements. Then listen to the news and check (?) the true or () false statements.

1. Researchers found that a combination of whipping and stomping forces is what causes laces to unravel without warning.

2. The investigators noted that shoelace knots frequently fail when people are walking and sitting on the edge of a table and swinging their legs.

3. Researchers come to the conclusion that stepping and swinging somehow might work together to foil footwear security.

4. The researchers confirmed that some knots are stronger than others. The granny knot is fairly weak and prone to failure, perhaps because the knot winds up twisted when pulled tight.

5. The researchers could determine whether different types of laces are more likely to produce ties that bind.

◆KEY

√1. Researchers found that a combination of whipping and stomping forces is what causes laces to unravel without warning.

×2. The investigators noted that shoelace knots frequently fail when people are walking and sitting on the edge of a table and swinging their legs.

√3. Researchers come to the conclusion that stepping and swinging somehow might work together to foil footwear security.

√4. The researchers confirmed that some knots are stronger than others. The granny knot is fairly weak and prone to failure, perhaps because the knot winds up twisted when pulled tight.

×5. The researchers could determine whether different types of laces are more likely to produce ties that bind.

时长：2.3分钟

语速：173wpm

来源：刘立军、宋葳 2017-09-27

练习 | 科学美国人：鞋带为什么会松

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