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You've probably seen footage of the Tacoma Narrows Bridge collapse in 1940 (if not, it's all over the internet).
大家或许看过1940年塔科马海峡吊桥倒塌的视频片段（如果没看过，请自行百度）。
And while I've heard that in Seattle they just call it bad bridge building,
在西雅图，他们称这座桥是垃圾桥梁建筑，
most teachers and physics textbooks have probably told you that the bridge collapsed because of resonance with the wind. But they're wrong!
但大部分老师和物理教科书可能都告诉过你，这座桥之所以倒塌了，是因为与风产生了共振。但是他们说错了！
That's because a resonance is a vibration driven by a source oscillating at a similar frequency -
共振指的是，物体在与其固有频率相同的震源下振动——
like how a swing at the park goes higher and higher as you push it,
比如公园里的秋千荡得越来越高，
or the electrons in an antenna move in tandem with the electromagnetic waves of a radio signal,
天线中的电子与无线电信号的电磁波同步移动，
or how a guitar string vibrates or wine glass shatters if you sing at just the right pitch.
或是吉他弦的震动方式，或是高音震碎玻璃杯。
And that's not what happened at the Tacoma narrows,
但是这些都不是塔科马海峡吊桥倒塌的原因，
because people at the bridge that day measured the windspeed as being fairly constant, or, 'not-oscillating.' So there was no forced resonance.
因为在那一天，桥上的人测量到的风速是相当恒定的，或者说“没有振荡”。所以就没有强迫共振。
It's also tempting to think that the bridge collapsed because of vortex shedding,
也有人用漩涡脱落来解释这个事件，
a cool-looking fluid process where vortices take turns sloughing off of the edge of an object - but that's not right either.
一种看起来很酷的流体现象，漩涡轮流从物体边缘脱落——但这也不对。
What did cause the bridge to collapse is a phenomenon called aeroelastic flutter –
导致桥梁倒塌的是一种被称为气动弹性震颤的现象——
the same thing that causes a strip of paper or blade of grass to vibrate if you hold it tight and blow straight at the edge.
这和拉紧一张纸或叶子的边缘并吹气所引发振动的原理相同。
Basically, with enough wind speed, the bridge started to twist a little bit -
基本上，有了足够的风速，桥就会开始轻微扭曲——
but then gravity and tension in the bridge caused it to twist back down, except too far!
但除非扭过头，否则桥上的重力和张力会迫使桥面扭回去！
So now the wind could push it in the opposite direction, causing it to twist more violently.
所以现在风可以把它推向相反的方向，使它扭曲得更剧烈。
And so on and so forth until, well… the bridge fluttered itself into destruction!
一直继续继续，直到桥梁把自己给扭废了。
And aeroelastic flutter isn't just limited to bridges - it can cause airplane wings to hum annoyingly, or vibrate so vigorously as to disintegrate.
气动弹性震颤现象不仅限于桥梁——它可以使飞机的机翼嗡嗡作响，或者剧烈振动，以至解体。
But don't worry - the last time this happened on a commercial airplane was in the early 1960s.
但不要担心——上一次客机发生这种事还是在20世纪60年代初期。
You should probably be more concerned with the haunted swingset in Firmat, Argentina that can swing on its own for days -
你可能更应该关注的是阿根廷Firmat市闹鬼的秋千，它可以自己荡好几天——
oh wait, no, that's just aeroelastic flutter. Sorry ghosts - physics just blew you away.
但这也只是因为气动弹性震颤现象。不好意思小鬼们——物理把你们拆穿了。
