This is Scientific American — 60-Second Science. I'm Christopher Intagliata.
Knuckles cracking. You may not mind the sound. You may despise it. Or you could study it.
Couple years back, Vinny Suja was taking a biomechanics class at the French Polytechnic School, outside Paris. And he was on the hunt for the perfect class project.
"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 one day and that's when I realized—'Huh, that's interesting.'"
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.
Or so they thought—because in 2015 shots were fired, in the form of MRI visualization of the knuckles post-cracking.
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 a model could help people better understand the origin of this sound."
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.
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.
(more cracking sounds)
Thanks for listening for Scientific American — 60-Second Science. I'm Christopher Intagliata.
这是扳指关节的声音 。你可能不在意这种声音，也可能会鄙视这样的声音 。或者你可以研究这种响声 。
几年前，威尼·苏加在巴黎郊外的法国理工学院攻读生物力学课程 。他当时在寻找完美的研究课题 。
“尽管他们提出了许多研究课题，可是我还没找到既实用又能在课堂框架内完成的课题 。当时我很沮丧，有一天我在扳指关节时意识到，‘哈，那很有意思 。'”
一个研究课题就这么诞生了：扳指关节的物理学原理 。这实际上是一项严肃的科学调查 。早在1971年，科学家就已经了解了扳指关节的原理：指关节周围液体中的气泡破裂发出响声 。
事实上，指关节扳响后气泡依然存在 。整个过程发生得太快，以致于影像技术无法实时显示，我们要以每秒1200帧的速度进行拍摄，这一速度比市面上最好的X光机和核磁共振仪器快10倍 。“那时我们意识到，一种模型可以帮助人们更好地理解这种声音的来源 。”
因此，苏加和同事阿卜杜勒·巴拉卡特利用数学模型发现，气泡局部坍塌就能产生同样大小的响声，这也许可以解释2015年研究人员在关节响后仍能看到气泡的原因 。详细情况发表在《科学报告》期刊上 。
谢谢大家收听科学美国人——60秒科学 。我是克里斯托弗·因塔利亚塔 。
1. even though 即使；尽管；纵然；
We lost the game, even though everyone played well.
2. in fact 事实上，其实；
In fact, things could get worse in the short run.
3. in real time 实时地；及时的；实时的；
So the data is shared in real time, and the problem of data staleness is eliminated.
4. on the market 在出售；
Commodity prices remain stable and there are plenty of goods on the market.