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

 

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.

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1 specialized   

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   

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   

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   

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   

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   

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。