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美国国家公共电台 NPR Why Some Rope Knots Hold Better Than Others

时间:2020-01-06 03:15来源:互联网 提供网友:nan   字体: [ ]
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AILSA CHANG, HOST:

Knots have been used by people since ancient times. There are thousands of different kinds of knots, everything from simple knots used to tie shoes to the far more specialized1 ones used by, say, mountaineers. Scientists have now come up with some basic rules that can be used to predict how a knot will perform. NPR's Nell Greenfieldboyce reports.

NELL GREENFIELDBOYCE, BYLINE2: There's a whole field of mathematics that studies knots theoretically to explore abstract properties of idealized curves.

VISHAL PATIL: But that's not what you care about if you're, for example, a sailor or a climber and you need to tie something which holds.

GREENFIELDBOYCE: Vishal Patil is a graduate student at MIT. He's interested in the mechanics of real-world knots. He says, take two simple knots - the reef knot and the granny knot. They look very similar but behave very differently.

PATIL: So if you pull on the reef knot, it tends to hold. And if you pull on the granny know, it tends to slip quite easily.

GREENFIELDBOYCE: He says there's been no theoretical framework, no set of rules to explain why these knots do what they do. But then he heard of something new, a special kind of fiber3 developed by colleagues at MIT. This fiber changes color when it's under strain.

PATIL: And we thought that this was a good opportunity to learn more about real physical knots using their system.

GREENFIELDBOYCE: The research team tied a couple of different knots in this fiber, and the color changes let them see how forces and strain were distributed inside the knots. They used this information to fine tune4 some computer simulations of knots. After that, they took what they'd learned and came up with a system for identifying strong knots and weak knots.

Patil says one key thing - the thing that separates the reef knot from the granny knot - is twist.

PATIL: Twist is quite important in how knots behave.

GREENFIELDBOYCE: He says when you have lots of twists going in opposite directions along the knot, it locks the knot.

PATIL: But if lots of twists are going in the same direction, then the whole thing can roll out.

GREENFIELDBOYCE: Other key features include the amount of friction5 in the knot and its overall complexity6. To see how well their system could predict a knot's behavior, they took six different knots and assessed how stable they should be. Then they tested that experimentally.

PATIL: We tried tying different knots and loading them with weight and seeing how much weight we needed to get them to slip.

GREENFIELDBOYCE: Their predictions were right. The research is reported in the journal Science, and it could someday be used to design new kinds of knots that are custom-made for certain jobs.

Nell Greenfieldboyce, NPR News.

(SOUNDBITE OF NEW JACKSON SONG, "PUT THE LOVE IN IT")


点击收听单词发音收听单词发音  

1 specialized Chuzwe     
adj.专门的,专业化的
参考例句:
  • There are many specialized agencies in the United Nations.联合国有许多专门机构。
  • These tools are very specialized.这些是专用工具。
2 byline sSXyQ     
n.署名;v.署名
参考例句:
  • His byline was absent as well.他的署名也不见了。
  • We wish to thank the author of this article which carries no byline.我们要感谢这篇文章的那位没有署名的作者。
3 fiber NzAye     
n.纤维,纤维质
参考例句:
  • The basic structural unit of yarn is the fiber.纤维是纱的基本结构单元。
  • The material must be free of fiber clumps.这种材料必须无纤维块。
4 tune NmnwW     
n.调子;和谐,协调;v.调音,调节,调整
参考例句:
  • He'd written a tune,and played it to us on the piano.他写了一段曲子,并在钢琴上弹给我们听。
  • The boy beat out a tune on a tin can.那男孩在易拉罐上敲出一首曲子。
5 friction JQMzr     
n.摩擦,摩擦力
参考例句:
  • When Joan returned to work,the friction between them increased.琼回来工作后,他们之间的摩擦加剧了。
  • Friction acts on moving bodies and brings them to a stop.摩擦力作用于运动着的物体,并使其停止。
6 complexity KO9z3     
n.复杂(性),复杂的事物
参考例句:
  • Only now did he understand the full complexity of the problem.直到现在他才明白这一问题的全部复杂性。
  • The complexity of the road map puzzled me.错综复杂的公路图把我搞糊涂了。
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TAG标签:   NPR  美国国家电台  英语听力
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