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For this video Lego sent me some of their Saturn V rocket sets.
为了这个视频，乐高送给了我一些他们的土星5号火箭套装。
But this isn't a video about space - I actually want to talk about the physics of how to keep tall things from shaking, like how to keep skyscrapers from swaying too much in the wind, or in an earthquake.
但这不是一个关于太空的视频——我实际上想谈谈如何防止高大物体晃动的物理原理，比如如何防止摩天大楼在风中或地震中过度摇晃。
The taller something is, the more liable it is to sway back and forth, so to demonstrate this, the Saturn V seemed by far like the best and coolest Lego set for the job (even if not the most realistic).
越高的东西越容易来回摇摆，所以为了证明这一点，土星5号似乎是目前为止最好、最酷的乐高组合(即使不是最现实的)。
If you don’t want your tall thing to sway, either because you’re worried it’ll fall apart or you’re worried it’ll freak out the people inside, you could just make it stiffer – either by adding more stuff or using more rigid materials – this isn’t always the most elegant solution, and gets expensive fast.
如果你不想让你高大的东西摇摆，要么是因为你担心它会散架，要么是因为你担心它会吓到里面的人，你可以让它更硬一些 ---要么加入更多的材料，要么使用更坚硬的材料---这并不总是最优雅的解决方案，而且代价很快就会变得昂贵。
But there’s another, clever solution.
但还有另一个聪明的解决办法。
From a physics perspective, a tall thing like a building is really an upside-down pendulum- when it gets bent a little bit to one side, the building’s natural stiffness pulls it back the other way, and so on.
从物理学的角度来看，像建筑物这样高的东西实际上是一个倒立的钟摆——当它稍微向一侧弯曲时，建筑物的自然刚度就会把它向后拉，以此类推。
And there's a neat phenomenon that happens with pendulums when you attach two of them together with a spring: they start swapping energy back and forth – first one oscillates, then both together, then the other has all the oscillations, then the first again, and so on.
当你用弹簧把两个摆连在一起它们开始来回交换能量第一个摆振荡，然后两个都振荡，然后另一个摆所有的振荡，然后第一个摆再次振荡，以此类推。
The same thing happens with solid blocks and springs, too, or any two oscillating things that are coupled together.
同样的事情也会发生在固体块和弹簧上，或者任何两个耦合在一起的振动物体上。
In a perfect frictionless simulation this energy swapping will go on forever.
在完美的无摩擦模拟中，这种能量交换将永远持续下去。
But in the real world there's friction and air resistance and the spring itself might heat up, causing the objects to lose energy, and the oscillations dampen over time.
但在现实世界中，存在摩擦和空气阻力，弹簧本身可能会升温，导致物体失去能量，随着时间的推移，振动会减弱。
And this phenomenon is what you can use to ‘discourage’ your upside-down pendulum from shaking in ways you don’t want it to.
你可以用这种现象来“阻止”你的倒立钟摆以你不想看到的方式晃动。
A big tall object is going to want to sway back and forth at its own natural frequency of swaying (which depends on its height, weight, and stiffness).
一个高大的物体将会以它自己的自然摇摆频率来回摇摆(这取决于它的高度、重量和硬度)。
If you then attach a smaller object to it that can sway to and fro, and add a little bit of friction, then any time the big object trades its energy to the little object,
如果你把一个可以来回摇摆的小物体附在它上面，并增加一点摩擦力，那么任何时候大物体的能量都会交换到小物体上，
the little object loses the energy to friction rather than trading it back to the big object, and this dampens out the big object's oscillations.
小物体因摩擦而失去能量，而不是将能量转换回大物体，这就抑制了大物体的振动。
In practice, you normally put the little object inside the big object, which looks more like this, but the principle is the same.
在实践中，你通常会把小对象放在大对象里面，看起来更像这样，但原理是一样的。
And you don’t want to use just any old little object and any old spring.
你不会想用任何旧的小物体和旧的弹簧。
It turns out that for a particular big thing, there’s an optimal combination of weight and friction and spring strength for the little object.
事实证明，对于一个特别大的物体，有一个最佳的重量，对于这个小物体，有一个最佳的摩擦力和弹簧强度的组合。
And only with your setup perfectly tuned will you get the fastest possible loss of energy and the best slowing down of the shaking.
只有把你的设置调好，你才能尽可能快地损失能量，并最好地减缓晃动。
That’s why this setup is called a “tuned mass damper” – “damper” because it dampens the swaying, and “tuned” because the little object is specifically tuned to steal energy from this particular big thing’s natural tendency to swing.
这就是为什么这个装置被称为“调谐质量阻尼器”——“阻尼器”是因为它抑制了摇摆，而“调谐”是因为这个小物体被专门调谐来从这个大物体的自然摆动趋势中窃取能量。
Which brings us to the Lego Saturn V rockets: in one of the rockets I’ve put a weighted pendulum in the place the lunar module should go, while the other just has the weights stuck in place.
这让我们想到了乐高土星5号火箭:在其中一个火箭中，我在登月舱应该去的地方放了一个带重量的钟摆，而另一个则把重量固定在原地。
If all goes well, and if I’ve done my math right, then when I bump the table, the rocket with the pendulum should sway a lot less than the rocket without.
如果一切顺利，如果我的计算正确，那么当我撞到桌子时，有钟摆的火箭会比没有钟摆的火箭摆动得小得多。
As you can see, the tuned mass damper does actually help!(though it’s a bit subtle).
如你所见，调谐质量阻尼器确实有帮助! (虽然有点微妙)。
Here’s a graph of the motion of the rocket in each case, which makes it more obvious.
这是每一种情况下火箭运动的图表，这使它更明显。
And though tuned mass dampers definitely weren’t used in the saturn V rocket in this way (since this is where the lunar module went),
虽然调谐质量阻尼器在土星5号火箭上绝对没有这样使用(因为这是登月舱所在的位置)，
they are used in skyscrapers and even in other things that aren’t buildings (though they’re usually hard to notice).
但它们被用于摩天大楼，甚至其他非建筑物(尽管它们通常很难被注意到)。
For example, if you look closely at power lines, a lot of them have this little dumbbell thing on them, which is a tuned mass damper that keeps the lines from shaking too vigorously in the wind.
例如，如果你仔细观察电线，很多电线上都有这个哑铃状的东西，这是一个调谐质量阻尼器，可以防止电线在风中剧烈晃动。
And tuned mass dampers have been used to reduce unwanted vibrations in airplane engines, formula 1 racing cars, and audio speaker cones.
调谐质量阻尼器已被用于减少飞机引擎、一级方程式赛车和音频扬声器锥体的不必要振动。
So there you go – the tuned mass damper, aka the physics of how to use little things to keep big things under control!
这就是调谐质量阻尼器，也就是如何用小物体阻止大物体晃动的物理学!
