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你能让铅笔平衡多长时间 – 译学馆
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你能让铅笔平衡多长时间

How Long Can You Balance a Pencil?

让铅笔或者其他头重脚轻的物体立起来 是个危险的工作
Balancing a pencil or any other top heavy object on its tip is quiet precarious task
很容易看出为什么重的物体不稳定
It’s easy to see why top heavy objects are unstable
他们就是 想要倒下
They just…Wanna fall down
任何轻微的推动都会破坏平衡
Any little nudge will put it off balance
重力作用更会使物体失去平衡 直到
with gravity happy to pull its center of mass even more off balance and the more off balance it is, the more gravity pulls until…
物理学家把它叫做倾斜的倒立钟摆 因为它就像一个反过来的钟摆
Physicist call this kind of tipping an Inverted pendulum, becouse it´s kind of like upside down pendulum.
关于倒立钟摆的数学分析 会让你对此感到显然
And careful mathematical analysis of inverted pendulums will tell you the obvious:
它很不稳定 理论预测 若理想笔尖使铅笔平衡
They’re really unstable. In fact, these equations predict that if a perfectly balanced pencil with a perfectly sharp tip
被推动万分之一个原子的宽度
were to get nudged off balance by just 1/10000th of the width of an atom,
它就会在三秒后倒下
it would take only three seconds to fall over.
确实有杂技演员可以用一个杆子让上面的另一个演员保持平衡
There are indeed acrobats who can balance poles with other acrobats on top,
也有机器人可以平衡 抓住 并且丢出竖直的杆子
and robots that can balance and catch and throw upright sticks,
还有人可以做出看上去不可能的艺术石堆
and people who make seemingly impossible artistic rock stacks.
但是在这些情况下 让物体平衡 要么需要主动维持平衡
But in all these cases, keeping the objects balanced either requires an active stabilization effort,
其他需要小心摆放的物品 事实上它们的平衡点都不是一个真的点
or else carefully taking advantage of the fact that the balancing point isn’t actually a point.
所以问题是 你能让一个有一个原子大小笔尖的铅笔平衡立住
So the question is this: can you balance a pencil sharpened to a perfect single atom wide tip
而不去人为保持平衡吗
on its tip, without active stabilization?
首先 你最好去除铅笔周围的气流
Well, to start, you’d better get rid of all the air bumping off the sides of the pencil,
因为一个氧分子的动能足够让铅笔动摇
since the kinetic energy of a typical oxygen molecule is enough to destabilize the pencil
记住 如果铅笔只是歪了万分之一个原子宽度
Remember: if the pencil gets off-centered by even 1/10000th the width of an atom,
它就会在三秒内倒下
it’ll fall down in under three seconds.
然后你要尽可能让铅笔和桌子降到绝对零度
And you’d better cool the pencil and table down as close to absolute 0 as you can,
因为原子越热越会产生热抖动 类似的抖动也会让铅笔不平衡
since the thermal jiggling of their atoms when they’re hotter will similarly jiggle the pencil off balance.
但是这时 物质在小范围内会有扩散性的波动样的性质
But even then, matter at very small scales has a spread-out, wave-like nature
也就是说 你不能让铅笔保持直立
which means you can’t have both the pencil perfectly upright
同时不移动
and not moving at the same time.
并且这个量子效应不是真实生活中平衡铅笔的抑制剂
And while this quantum effect is never a real life inhibitor of precarious pencil balancing,
这意味着你永远不可能成功
it means you never even COULD succeed.
然而 测试铅笔可以在指尖立多久也是件有趣的事
However, it’s still fun to see how long you can keep a pencil balanced on your fingertip.
铅笔越短越难立住
The shorter the pencil, the harder it is.
我最好的成绩是19厘米的铅笔立住1.3秒
My best time for a standard 19 cm pencil was 1,3 seconds.
你可以打破这个记录吗
Think you can beat it?
这个一分钟物理是Audible.com提供的
This minutephysics video was brought to you by Audible.com,
这是在所有媒体中领头的有声书供应网站
one of the leading providers of online audiobooks across all types of media
包括 科幻的 非科幻的 和期刊
including fiction, non-fiction, and periodicals.
我这星期推荐Malcolm Gladwell 的Tipping Point
I’d like to recommend The Tipping Point by Malcolm Gladwell this week.
这本书是关于扩散趋势的指数增长 社会流行趋势这类的东西
It’s a book about exponential increases in spreads, uh, trends, social trends epidemics, that sort of thing.
并且这个计算方式和让物体立住的方程
And, uh, it’s – the mathematic is somewhat related to the mathematics of
有一些关联 所以不管怎么说 我推荐这本书
balancing an object on its… tip, so, anyway, The Tipping Point, by Malcolm Gladwell.
Audible.com赞助了一分钟物理 没有它们我们就做不到这些
Audible.com supports minutephysics and without them, we wouldn’t be able to do what we do, so…
感谢Audible的支持 点击链接以获取免费有声书
Thank you to Audible, and, uh, head to audible.com/minutephysics to get your free audiobook.

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