评论
打印
You've probably seen footage of the Tacoma narrows bridge collapse in 1940
也许你看过1940年塔可马大桥倒塌的视频
(if not, it's all over the internet).
如果没看过 去百度一下
And while I've heard that in Seattle they just call it bad bridge building,
而在西雅图 人们称桥为"渣作"
most teachers and physics textbooks have probably told you that
大多老师和物理教材都写道
the bridge collapsed because of resonance with the wind.
桥倒塌的原因是与风产生了共振
But they're wrong!
但他们错了
That's because a resonance is a vibration driven by a source oscillating at a similar frequency -
因为共振是指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,
就像公园的秋千随着你的推动越摆越高
or the electrons in an antenna move in tandem with the electromagnetic waves of a radio signal,
或是电磁波使天线中的电子来回移动
or how a guitar string vibrates
或是吉他弦的震动方式
or wine glass shatters if you sing at just the right pitch.
或是高音震碎玻璃杯
And that's not what happened at the Tacoma narrows,
这都不是塔可马大桥倒塌的真相
because people at the bridge that day measured the windspeed
因为当天现场测量的风速
as being fairly constant,
显示风速相当稳定
or, 'not-oscillating.'
或者说是"非震荡的"
So there was no forced resonance.
所以没可能造成共振
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
一种高大上的流体现象
where vortices take turns sloughing off of the edge of an object
流体在脱离物体边缘时会形成漩涡
- but that's not right either.
不过这也不对
What did cause the bridge to collapse is a phenomenon
造成桥梁垮塌的真相只有一个
called aeroelastic flutter
就是气动弹性震颤
– the same thing that causes a strip of paper or blade of grass to vibrate
这和拉紧一张纸或叶子的边缘时
if you hold it tight and blow straight at the edge.
吹气引发振动的原理相同
Basically, with enough wind speed,
事实上 风速足够大时
the bridge started to twist a little bit -
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!
除非扭过头 重力和张力会迫使桥面扭回去
So now the wind could push it in the opposite direction,
此时风就会将桥推向另一边
causing it to twist more violently.
造成更为强烈的扭曲
And so on and so forth until, well… the bridge fluttered itself into destruction!
如此这般 直到桥梁把它自己扭废了
And aeroelastic flutter isn't just limited to bridges -
而且气动弹性震颤并不局限于桥梁
it can cause airplane wings to hum annoyingly,
它也会使飞机机翼发出烦人的响声
or vibrate so vigorously as to disintegrate.
或者解体
But don't worry -
别担心
the last time this happened on a commercial airplane
上一次客机发生这种事
was in the early 1960s.
还是在20世纪60年代
You should probably be more concerned with the haunted swingset in Firmat, Argentina
阿根廷Firmat市的一个闹鬼的秋千更好玩
that can swing on its own for days -
它能自己high上几天
oh wait, no, that's just aeroelastic flutter.
但这只是因为气弹性震颤
Sorry ghosts -
对不起 小鬼们
physics just blew you away.
物理把你们拆穿了
