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Ripping a gigantic, thousand-page phone book in half sounds like a feat that's reserved only for the strongest people.
把一本一千页的电话簿撕成两半听起来像是只有最强壮的人才能完成的壮举。
But with the help of a bit of physics, this giant artifact from a bygone age can crumble. Well, tear.
但借助一点物理学，这个来自远古时代的巨大制品可能会破碎。好了，撕吧。
The idea is to use properties that all materials have in common to weaken the book until it gives way.
其理念是利用所有材料都具有的特性来削弱这本书，直到它屈服为止。
And that tells us something about how things fail. The trick is to create a deep crease in the book.
这向我们解释了事情是如何失败的。诀窍是在书上弄出一条深深的折痕。
This creates something called a stress concentrator.
所谓的应力集中点由此产生。
Stress concentrators are like pressure points that experience more force than other parts of an object.
应力集中点就像是比物体的其他部分承受更大力的压力点。
They work because of geometrical discontinuities like corners and cracks,
它们的工作原理是由于像角和裂缝这样的几何间断点
which change up how force is distributed in an object, basically concentrating it at that point.
改变了力在物体中的分布，将力基本就集中在那个点上。
Sharp corners or creases experience a lot more stress than, say, a flat part in the middle of an object.
锐化边角或折痕比物体中间的平坦部分承受更多的压力。
We pay a lot of attention to stress concentrators in the design of everyday things.
在设计生活物品时，我们非常重视应力集中点。
They're the reason why perforated paper is easier to tear,
它们是穿孔纸更容易撕碎的原因，
and why some food packages have a little cut to help you open them without scissors.
是一些食物包装袋上有尖角帮助你无需剪刀就能打开包装袋的原因。
They're even why airplane windows are oval instead of square,
它们甚至是飞机窗户是椭圆形而非方形的原因，
so there aren't any corners that might fail under pressure.
这样就没有任何一个角会在压力下崩溃。
One classic example that illustrates the effects of stress concentrators involves a rectangular plate
一个展示应力集中点效果的经典例子就是以相同的速度
that's being pulled at the same rate from the top and bottom.
从顶部和底部向外拉扯矩形板。
If the plate doesn't have any cracks or holes or other imperfections, it stretches out uniformly.
如果这个板子没有任何裂纹或孔洞或其他缺陷，它会均匀地伸展。
But if you cut a small notch in the plate, the force will be amplified around it, especially near the tip.
但是如果你在板子上切一个小缺口，它周围的力就会被放大，尤其是在口子尖端附近。
And the deeper or sharper that tip is, the more intense that force becomes.
尖端越深或越尖，力就越强。
Which means more and more force is concentrated in a small area,
这意味着越来越多的力集中在一个小区域
and the whole thing gives way at the site of that notch.
整个板子都会在缺口的地方垮掉。
But even if you've prepped your phonebook with the sharpest V you've ever made,
但即使你在电话簿上准备了一个最尖的口子，
having a stress concentrator won't magically make you rip a phonebook in half.
这个应力集中点也不会让你奇迹般地把电话簿撕成两半。
For each part of the phonebook you rip, you still need enough force
电话簿的每一个部分都需要足够的力
to exceed the tensile strength and tear strength of the pages you're tearing.
才能超过电话簿的抗拉强度和撕裂强度。
The tensile strength describes the force you need to create a rip in the paper,
抗拉强度是在纸张上撕开一道口子所需的力，
while the tear strength tells you how easy it is to keep tearing those pages once you've ripped them.
而撕裂强度会告诉你一旦你撕开了它们，再继续撕毁它们会有多么容易。
Pulling on the paper causes the fibers within the paper to separate or even break,
牵拉纸张会使纸内的纤维分离甚至断裂，
which in turn lets you rip, and keep ripping the paper.
反过来可以让你撕开并继续撕碎纸张。
Minimizing the number of pages you're tearing at one time also helps,
减少你一次撕掉的页数也有帮助，
since fewer pages require less force to break.
因为页数越少所需的力就越少。
The deep indentation helps with that, since it both concentrates the force you're applying,
深压痕有助于这一点，因为它既集中了你所施加的力
and means you're only working on a few pages at a time.
又意味着你一次只需专注于几页就可以了。
With some effort, it should be possible to get through an entire phone book this way.
通过一些努力，应该可以利用这种方式撕开整个电话簿。
Stress concentration doesn't only apply to small stuff like phone books and cheese packages.
应力集中点不仅仅应用于电话簿和芝士包装袋这样的小物件。
Structures like bridges, which have to carry a lot of weight,
如果有应力集中点的存在，
can give way prematurely if stress concentrators are present.
那么像桥梁这样需要承载很多重量的结构就会倒塌。
Which can be as a result of flaws in the overall design or just poor construction.
这可能是由于整体设计上的缺陷，也可能只是施工质量差。
We're not saying you should try tearing a phone book in half at your next party.
我们不建议大家在下次聚会上把电话簿撕成两半。
But we're also not saying you shouldn't. If you can even find a phone book these days, that is.
但我们也不是说大家不应该这么做，如果如今你还能找到电话簿的话。
Thanks for asking! And if you want to ask us a question like this that might get made into an episode,
感谢提问！如果你想向我们提问并希望这个问题被制成节目，
you can get access to our QQ inbox by becoming a patron over at patreon.com/scishow.
你可以登入patreon.com/scishow成为我们的赞助人并向我们的提问箱投稿。
And that also helps us continue making educational videos for everyone to enjoy, so we really appreciate it!
这也将帮助我们继续制作大家喜欢的教育性节目，非常感谢大家！
