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Oh, hi guys! Squeaks and I were just playing with some blocks.
噢，嗨，你们好！我和吱吱刚刚在玩积木。
You know, it may not seem like it,
它可能看起来不像，
but the cities and towns that we live in are all built using the same rules as our little pretend village over here.
但是我们居住的城镇是用同样的规则建造的，就像我们的模拟小村庄一样。
It's just that the real ones are bigger.
只不过真的大些罢了。
And one of our viewers, 6 year old Hannah from the UK, wanted to know how some of the things that we build stay standing.
我们的一个6岁观众，来自英国的汉娜，想知道我们的建筑如何保持固定。
So she sent us a really great question, "Why are bridges so strong?"
于是她问了一个很好的问题：“桥为什么那么坚固？”
Excellent question. Sometimes when a road or railroad track needs to go across something big like a river or deep valley,
问题不错！有时公路或铁路的轨道需要穿过河流或深谷之类的大面积区域，
experts called engineers design and build bridges to do that job.
工程师设计并建造桥梁来完成这份工作。
And bridges can be really busy.
桥梁可能非常忙碌。
Take for example what's said to be the world's busiest bridge, the George Washington Bridge in New York City.
以世界上最繁忙的大桥——纽约的乔治华盛顿大桥为例，
Look at all those cars and trucks!
看看这些汽车和卡车！
It has to be pretty sturdy to carry so many people and cars.
要承载这么多的人和车需要桥梁相当坚固。
For a bridge to carry that much weight, it has to be built of special material, like iron and steel.
桥要承载这么多的重量，需要用特殊的材料建造，比如铁和刚。
But it takes more than tough materials to make a strong bridge.
但建造坚固的桥梁不仅需要坚韧的材料。
So let's look at how bridges work.
那么让我们看看桥是如何工作的吧。
One very simple kind of bridge is called a beam bridge.
有一种非常简单的桥，叫梁桥。
When we say simple, we really do mean simple.
说到简单，就是它的字面意思。
A beam bridge can be just a log that you use to walk across a stream.
梁桥可以是你用来穿过小溪的一根木头。
Or put a long strip of cardboard between two short blocks.
或是两个短积木之间放得一个长条纸板。
That's a beam bridge too.
那也是梁桥。
All bridges can hold a certain amount of weight,
所有的桥梁都可以承载一定的重量，
but what happens if we put too much weight on a beam bridge? Let's find out.
但如果我们在梁桥上放太多的重物，会发生什么呢？让我们找出答案。
It collapses. So a bridge that carries trucks and cars, which are very heavy,
它塌了。因此，一座能承载重卡车和汽车的桥梁，
would have to be stronger than a bridge that carries bikes or people on foot, which are lighter.
比承载自行车和行人的桥更坚固，因为自行车和人较轻。
So how do we make stronger bridges?
那么，我们如何建造更坚固的桥梁呢？
Well, over time, people have learned that certain shapes can be used to make stronger bridges.
随着时间的推移，人们已经了解到某些形状可以用来建造更坚固的桥梁。
Take a look at this railroad bridge.
看这座铁路桥。
It has to be strong because it carries trains. What shape do you see?
它必须坚固，因为它要承载火车。你看到了什么形状？
That's right, triangles. And that's not by accident.
说对了，三角形。这不是偶然。
The fact is, triangles are really strong shapes for building.
事实上，三角形对于建筑来说是很坚固的形状。
If you put force on one side of a triangle, it bends.
如果你在三角形的一边施力，它会弯曲。
But if you put force on its point, it keeps its shape.
但如果在顶点施力，它的形状不变。
That's because the two sides of the triangle are pushed down by the force and the bottom gets stretched out to both sides.
这是因为三角形的两边都被力压下去了，底边延伸到两边。
Each side feels the force, but none of them bends,
每边都感受到了力，但都没弯曲，
and this makes the triangle a really sturdy and stable shape.
这让三角形非常坚固，且形状稳定。
This is why you'll see lots of triangles in bridges,
这就是为什么你会在桥上看到很多三角形，
both above the part that you actually travel on, called the deck, and below it.
在你行走的桥面上和下面都有很多三角形。
The long string of triangles that you see in a bridge is called a truss.
你在桥上看到的长串三角形叫做桁架。
Trusses help a bridge spread out the weight that it has to carry.
桁架帮助桥梁将其承载的重量散开。
But not all bridges are made of trusses.
但并非所有的桥梁都由桁架构成。
If a bridge has to cross a really wide body of water, it might be too difficult or expensive to build a truss bridge.
如果桥要跨过一个很宽的水域，建造桁架桥可能非常困难，而且造价昂贵。
So engineers designed another kind of bridge called a suspension bridge.
于是工程师们设计了另一种桥梁，叫做悬索桥。
The Golden Gate Bridge in California is a great example of a suspension bridge.
加州的金门大桥是悬索桥的典范。
Suspension bridges work by using a force called tension.
悬索桥利用拉力工作。
Tension is just pulling something tight.
拉力是拉紧物体的力。
Suspension bridges are made of a deck that's hung, or suspended from thick cables
悬索桥由粗钢索悬挂的桥面制成，
that stretch from one side of the bridge to the other.
钢索从桥的一侧穿到另一侧
These cables are supported by tall towers and then are held down tightly, or anchored on both ends.
这些钢索由高塔支撑，然后被紧紧拉住，或者锚定在两端。
Suspension bridges are strong because the force on the bridge gets spread out.
悬索桥很坚固，因为桥上的力散开了。
The weight of the cars or trains or horses, whatever's traveling across it, pulls on the cables, creating tension.
汽车、火车或马的重量，不管它上面穿行的是什么，都会拉钢索产生张力。
Those cables then pull down on the towers
然后那些钢索往下拉高塔，
and also pull on the anchors on either end of the bridge to hold up the deck.
同时在桥的两端拉锚来支撑桥面。
I could go on and on about all kinds of clever bridges,
我可以继续讲各种灵巧的桥梁，
but basically, bridges are strong not only because they're made of strong materials,
但根本上来说，桥梁之所以坚固，不仅是因为材料坚韧，
but also because of the smart designs dreamed up and planned by engineers.
同时也因为工程师们想出的聪明设计。
So thanks for asking, Hannah, and thank you for hanging out with us at SciShow Kids.
所以，汉娜，感谢你的提问，也感谢你们陪伴儿童科学秀。
See you next time.
我们下期见。
