科学美国人60秒 打响指的惊人物理现象（在线收听）

The Surprising Physics of Finger Snapping

打响指的惊人物理现象

Karen Hopkin: This is Scientific American’s 60-Second Science. I’m Karen Hopkin.

Doing science isn’t easy. It takes an enormous amount of time and energy to collect and analyze data. At least, that’s the way it usually works.

凯伦·霍普金：这是《科学美国人》的60秒科学。我是凯伦·霍普金。

做科学并不容易。收集和分析数据需要花费大量的时间和精力。至少，这是它通常的工作方式。

Saad Bhamla: This is one of those examples that we joke that we can snap our fingers and get data.

萨阿德·巴姆拉：这是我们开玩笑说我们可以折断手指获取数据的例子之一。

Hopkin: That’s because Saad Bhamla and his students just wrapped up a study of the physics of finger snapping. They found that the right amount of friction is key to a successful snap. Their work appears in the Journal of the Royal Society Interface. [Raghav Acharya et al., The ultrafast snap of a finger is mediated by skin friction]

霍普金：那是因为萨阿德·巴姆拉和他的学生刚刚完成了一项关于手指折断的物理研究。他们发现适当的摩擦力是成功抓拍的关键。他们的研究成果发表在《皇家学会杂志》上。

Bhamla’s lab at Georgia Tech focuses on ultrafast motion in nature.

Bhamla: Organisms can achieve really, really fast motions, and we are curious about how they’re able to do this and how we may extract those principles for perhaps synthetic systems.

巴姆拉在佐治亚理工学院的实验室专注于自然界的超快运动。

巴姆拉：生物体可以实现非常非常快的运动，我们很好奇它们是如何做到这一点的，以及我们如何为可能的合成系统提取这些原理。

Hopkin: Their science may be hard-core. But their lab meetings include time to be a bit more playful.

霍普金：他们的科学可能是核心。但是他们的实验室会议包括时间变得更有趣一点。

Bhamla: We have something called Super Happy Fun Time. And in this, we’ll talk about something typically nonscientific just to kind of defuse the situation after a typically intense scientific discussion that a student presents.

巴姆拉：我们有一种叫做“超级快乐时光”的活动。在这篇文章中，我们将讨论一些典型的非科学的东西，只是为了在一个学生典型的激烈的科学讨论之后缓解这种情况。

Hopkin: A couple years back, their talk turned to the movie Infinity Wars. In the climax of this Avengers flick, supervillain Thanos forever alters the Marvel Cinematic Universe with a snap of his massive, metal-clad fingers. But something about the scene left Bhamla scratching his head.

霍普金：几年前，他们的话题转到电影《无限战争》。在这部《复仇者》电影的高潮中，超级反派塔诺斯用他那硕大的金属手指的一瞬间永远改变了奇迹般的电影世界。但现场的一些情况让巴姆拉抓挠着头。

Bhamla: And I said, “You know what? I’m willing to make a bet that if you had metallic gauntlets like Thanos has, I would suspect that it’s actually very difficult to store energy in a controllable way.”

巴姆拉：我说，“你知道吗？我愿意打赌，如果你有像塔诺斯那样的金属护手，我会怀疑以可控的方式储存能量是非常困难的。”

Hopkin: Energy that then has to get quickly released if you really want to snap. So Raghav Acharya, a student in Bhamla’s lab, set up an experiment.

霍普金：如果你真的想抓拍的话，能量必须很快释放出来。因此，Bhamla实验室的学生Raghav Acharya进行了一项实验。

Bhamla: He put some reflective dots on his fingers so he could automatically track the finger movement when you take a side view video with a high-speed camera—just to be able to extract out the velocities and accelerations.

巴姆拉：他在手指上放了一些反射点，这样当你用高速摄像机拍摄侧视视频时，他就可以自动跟踪手指的运动，以便提取速度和加速度。

Hopkin: Because the first thing they wanted to know was: Just how fast is this jazzy hepcat gesture?

霍普金：因为他们想知道的第一件事是：这个爵士赫普卡特手势有多快？

Bhamla: We discovered that the finger snap takes about seven milliseconds. To put that into context, that’s 20 times faster than the blink of an eye. A blink of an eye is glacially slow: it’s like about 150 milliseconds.

巴姆拉：我们发现手指抓拍大约需要7毫秒。把它放在上下文中，比眨眼快20倍。眨眼的速度非常慢：大约150毫秒。

Hopkin: Even more impressive than its speed was its acceleration, which was three times faster than the throwing arm of a big-league baseball pitcher.

霍普金：比它的速度更令人印象深刻的是它的加速度，它比大联盟棒球投手的投球臂快三倍。

Bhamla: So here we have a snap done by scientists. So we’re no professional athletes; we barely go to the gym. And we’re about almost three times in acceleration faster. So that kind of led to this question: How are we able to perform this seemingly extraordinary feat of acrobatics and human dexterity?

巴姆拉：这里我们有一个由科学家拍摄的快照。所以我们不是职业运动员；我们几乎不去健身房。我们的加速度快了将近三倍。这就引出了一个问题：我们如何才能完成这个看似非凡的杂技和人类灵巧的壮举？

Hopkin: To find out, they started to fiddle with friction. First, Raghav and his grad student mentor Elio Challita used some moisturizer to make their fingers a little more slippery. And they found the resulting snaps were not so snappy. So then they went the other way.

霍普金：为了找到答案，他们开始玩弄摩擦。首先，Raghav和他的研究生导师Elio Challita使用了一些润肤霜，使他们的手指更加光滑。他们发现结果的快照并不那么快。于是他们走了另一条路。

Bhamla: Counterintuitively, we thought, “Oh, friction is great. Let’s put some high-friction rubber pads”—thinking, “If I increase the friction, I’m going to get a louder snap perhaps.”

巴姆拉：与直觉相反，我们认为，“哦，摩擦很好。让我们放一些高摩擦橡胶垫”——想，“如果我增加摩擦，我可能会得到更大的响声。”

Hopkin: But that also squelched the snap because you waste too much of the stored energy trying to get your fingers to slide past each other.

霍普金：但这也压制了这一瞬间，因为你浪费了太多储存的能量试图让你的手指滑过彼此。

Bhamla: And so it turns out that, in our experiments, we find that the skin friction is kind of this optimal sweet spot in this Goldilocks zone that gives you enough energy but also detaches quickly to give you the snap [snaps].

Bhamla：所以，在我们的实验中，我们发现表面摩擦力是这个金发区的一个最佳最佳最佳点，它能给你足够的能量，但也能很快分离，让你抓紧

Hopkin: And as for Thanos?

霍普金：至于塔诺斯呢？

Bhamla: If you put copper thimbles, which we did to test the Thanos hypothesis, turns out that the compressibility of the finger pads is important as well. If you have these rigid surfaces, although the friction is the same as the skin, not being able to compress affects the grip and storage of energy, so you get a very weak, or not really a satisfactory, snap.

巴姆拉：如果你放上铜套管，我们就是为了验证萨诺斯假说而做的，结果证明手指垫的可压缩性也很重要。如果你有这些刚性表面，尽管摩擦力与皮肤相同，但不能压缩会影响抓地力和能量储存，因此你会得到非常弱的，或者不是很令人满意的抓拍。

Hopkin: Bhamla wonders whether there’s also something special about the shape of our hands that gives us this ability. Or can other primates do it, too?

霍普金：巴姆拉想知道我们的手的形状是否也有特殊的东西赋予我们这种能力。或者其他灵长类动物也能这样做？

Bhamla: I have written so many e-mails to so many anthropologists, zookeepers.

巴姆拉：我给这么多人类学家、动物园管理员写了这么多电子邮件。

Hopkin: He’s even gone back to the movies.

霍普金：他甚至还回去看电影了。

Bhamla: What if I saw, in Planet of the Apes, these apes sitting on top of a horse and snapping? Well that would be okay for me because somebody at least imagined it, right? Maybe they did their homework. Maybe it was described in some journal somewhere by a naturalist.

巴姆拉：若我在《类人猿星球》中看到，这些类人猿坐在马背上偷吃呢？那对我来说没关系，因为至少有人想象出来了，对吧？也许他们做了家庭作业。也许是某个博物学家在某个杂志上描述的。

Hopkin: If you’ve ever seen a chimp snap, please let Bhamla know. In the meantime, he’ll continue to pursue projects that captivate his curiosity.

霍普金：如果你见过黑猩猩咬人，请告诉巴姆拉。与此同时，他将继续从事吸引他好奇心的项目。

Bhamla: Life is too short to do boring stuff. I think it’s more enjoyable for me and the students to say, “Oh my god, like, how cool is that?” And when nature pushes the limits of physics and engineering, there are interesting things to be gleaned out of it.

巴姆拉：生命太短暂，不能做无聊的事情。我认为对我和学生来说，说“哦，天哪，那有多酷？”更令人愉快当大自然突破物理学和工程学的极限时，我们可以从中收集到一些有趣的东西。

Hopkin: Plus, you can explain your findings like [snaps].

霍普金：另外，你可以这样解释你的发现

Bhamla: My parents now get it [laughs]. Well, I think they do.

巴姆拉：我父母现在明白了[笑]。嗯，我想是的。

Hopkin: For Scientific American’s 60-Second Science, I’m Karen Hopkin.

霍普金：《科学美国人》的《60秒科学》，我是凯伦·霍普金。