「涨知识」“掰指关节”为啥会发出咔咔声？
我们知道，在手指疲劳的时候，对指关节进行推拿会产生“哒哒哒”的爆裂声，但究竟是什么造成了这种声音的产生呢？
但由于发声时间短，科学家们一直未能给出一个确切的答案，最近又有科学家通过研究给出了解释。
Math Cracks a Knuckle-Cracking Mystery
破解“掰指关节”发出声音的奥秘
<<knuckle-cracking sound>>
Knuckles[1] cracking[2]. You may not mind the sound. You may despise[3] it. Or you could study it.
掰指关节时会发出咔嗒声。你可能没有注意到它的声音，你可能会讨厌这种声音，再或者你可以研究它。
[1]knuckle ['nʌk(ə)l]
one of the joints in the hand where your fingers bend, especially where your fingers join on to the main part of your hand 指节；（尤指）掌指关节
[2]crack (v.)：to make a sudden, short noise, or to cause something to make this noise （使）噼啪作响；（使）发出爆裂声
He's always cracking his knuckles (= pulling the joints of his fingers to make a noise).
他总是把自己的手指关节弄得噼啪作响。
[3]despise [dɪ'spaɪz]
to feel a strong dislike for someone or something because you think that that person or thing is bad or has no value 鄙视，蔑视；厌恶
The two groups despise each other.
这两个团体相互鄙视。
Couple years back, Vinny Suja was taking a biomechanics class at the French Polytechnic School, outside Paris. And he was on the hunt for[4] the perfect class project.
几年前，Vinny Suja在巴黎郊外的法国理工学院攻读生物力学课程。他正在寻找完美的课程项目来进行科研。
[4]hunt (n.)：a search for something or someone 搜寻，寻找
Police are on the hunt (= searching) for the kidnappers.
警方正在搜捕绑匪。
"Even though they suggested many projects, I couldn't find one which was both practical and that I could complete within the framework of this class. So in frustration, I was cracking my knuckles[2] one day and that's when I realized—'Huh, that's interesting.'"
“尽管他们提出了许多项目，但我找不到一个既实用又能在本课程框架内完成的项目，所以在挫折中，有一天我在掰着自己的指关节发出了声响，突然我意识到 - '呃， 有意思！'”
And so a project was born: the physics of knuckle cracking. It's actually a subject of intense scientific investigation. Back in 1971, scientists figured they knew how it worked: the cracking sound was caused by bubbles popping within the fluid surrounding the knuckles.
所以一个项目终于诞生了：掰指关节声响的物理学。它实际上是一项深入科学调查的课题。早在1971年，科学家们就发现了它产生的原理：发出的声音是由指关节周围流体内的气泡爆裂引起的。
<<cracking sound>>
Or so they thought — because in 2015 shots were fired, in the form of MRI* visualization of the knuckles post-cracking.
或者只能说是他们所认为的原理 - 因为在2015年对掰指关节后进行核磁共振成像的结果显示的并非如此。
*MRI也就是磁共振成像，英文全称是：Magnetic Resonance Imaging。
<<cracking sound>>
In fact, the bubbles were still there. The whole process happens too fast for imaging technology to visualize in real time—you'd need to shoot at 1,200 frames per second, 10 times faster than the best x-ray and MRI machines on the market. "And that's when we realized that a model could help people better understand the origin of this sound."
事实上，气泡仍然存在。 整个过程发生得太快，影像技术无法实时显示 - 您需要以每秒1200帧的速度进行拍摄，比市场上最好的X光机和MRI机器快10倍。 “那就是，当我们注意到一个模型，可以帮助人们更好地理解这种声音的起源。”
So, using mathematical models, Suja and his colleague Abdul Barakat found that just a partial collapse of the bubbles could cause cracking sounds of the same degree, which might explain why the 2015 researchers still saw bubbles after the crack. The details are in the journal Scientific Reports [V. Chandran Suja & A. I. Barakat, A Mathematical Model for the Sounds Produced by Knuckle Cracking].
因此，Suja和他的同事Abdul Barakat使用数学模型发现，气泡部分破碎的话，可能会产生同样程度的声音，这也许可以解释为什么2015年的研究人员在掰完指关节后仍看到气泡。
Further modeling of bubble behavior, both pre- and post-pop, will be needed, they say, before they're confident that they've truly cracked the case.
他们表示，在他们确信自己真正破解了这一谜团之前，需要对气泡破裂前和破裂后的一系列“行为”进一步建模。
英文来源：科学美国人
翻译部分来源：http://t.cn/RnB0OEL 仅供参考