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科学美国人60秒:茶壶为什么会嗖嗖叫?

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This is Scientific American — 60-Second Science. I'm Wayt Gibbs. Got a minute?

这里是《科学美国人》的60秒科学,我是韦特·吉布斯。准备好了吗?

British physicist Lord Rayleigh is best known for his discovery of argon and for explaining, in 1871, why the sky is blue. But he also puzzled over this: [sound of a kettle whistling].

英国物理学家瑞利勋爵(Lord Rayleigh)因发现了氩,以及在1871年解释了天空为什么是蓝色而闻名于世。但他也对一个问题感到困惑:茶壶为什么会嗖嗖叫?

Rayleigh knew that a kettle makes that sound when steam jets through the hole in a thick lid that has a gap in the middle. He speculated that the jet becomes unstable inside that gap, setting up an acoustic feedback loop within the gap. But he couldn’t prove it.

瑞利知道,当急速的蒸汽从有夹层的厚茶壶盖盖眼中喷出时,就会发出声响。他推测,气流会在夹层中变得很不稳定,从而形成一个声反馈回路。然而,他没法证明这个推测。

Now two engineers at Cambridge University claim to have solved the puzzle—and proved Rayleigh wrong. The work is in the journal Physics of Fluids. [R. H. Henrywood and A. Agarwal, The aeroacoustics of a steam kettle]

两位剑桥大学的工程师宣布他们解决了这个茶壶盖谜题——还证明了瑞利是错的。这一论文发表在《流体物理学》(Physics of Fluids)期刊上。

The engineers found that a kettle actually whistles in two distinct ways. It starts off with air vibrating in the gap between the layers of the lid, like when you do this [blow over an empty bottle] and this [whistle].

两位工程师发现,壶盖其实有两种截然不同的发声方式——刚开始时,是由于空气在夹层中的上下振动,就像你对着空瓶子吹气和吹口哨时一样。

But as the pressure builds, vortices of steam peel off from the jet exiting the lid. Each vortex creates sound waves at a frequency that depends on the length of the spout and the pressure inside it. Rising temperature means rising pressure, which produces a rising whistle. Which means it’s time for tea.

但当压力不断增大,喷出壶盖的气体会剥离出一股股涡流,并发出声音。声音的频率取决于喷口的长度与其中压力的大小。升温意味着加压,从而会提高音调,也意味着——你可以来一杯热茶了~

Thanks for the minute for Scientific American — 60-Second Science. I'm Wayt Gibbs.

感谢收听《科学美国人》的60秒科学。韦特·吉布斯报道。

This is Scientific American — 60-Second Science. I'm Wayt Gibbs. Got a minute?

British physicist Lord Rayleigh is best known for his discovery of argon and for explaining, in 1871, why the sky is blue. But he also puzzled over this: [sound of a kettle whistling].

Rayleigh knew that a kettle makes that sound when steam jets through the hole in a thick lid that has a gap in the middle. He speculated that the jet becomes unstable inside that gap, setting up an acoustic feedback loop within the gap. But he couldn’t prove it.

Now two engineers at Cambridge University claim to have solved the puzzle—and proved Rayleigh wrong. The work is in the journal Physics of Fluids. [R. H. Henrywood and A. Agarwal, The aeroacoustics of a steam kettle]

The engineers found that a kettle actually whistles in two distinct ways. It starts off with air vibrating in the gap between the layers of the lid, like when you do this [blow over an empty bottle] and this [whistle].

But as the pressure builds, vortices of steam peel off from the jet exiting the lid. Each vortex creates sound waves at a frequency that depends on the length of the spout and the pressure inside it. Rising temperature means rising pressure, which produces a rising whistle. Which means it’s time for tea.

Thanks for the minute for Scientific American — 60-Second Science. I'm Wayt Gibbs.


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