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Squeaks and I were outside the other day looking for shapes in the clouds
有一天吱吱和我在看云的形状
We found some clouds that looked like our friend Ruffles the Squirrel, and one that looked like a turkey, and even one that looked like the Fort!
我们发现一些云看起来像我们的朋友弄皱了松鼠，还有一些看起来像火鸡，甚至还有一些看起来像堡垒!
And that's not all we saw in the sky…
这并不是我们在天空中看到的全部……
We got to watch a jet plane fly overhead!
我们要看一架喷气式飞机从头顶飞过！
Squeaks noticed something interesting about it: there was a white trail that came out from the back of the airplane
吱吱注意到了一件有趣的事情：从飞机后部飞出了一条白色的轨迹
It looked like the plane was leaving a line behind it across the sky!
看起来飞机在空中留下了一条线！
Maybe you've seen this too — or maybe you didn't even see the plane, and only saw the trail it left behind
也许你也看到了，也许你甚至没有看到飞机，只看到了它留下的痕迹
Sometimes you can see them for a long time after the jet is gone
有时你会在飞机消失后很长一段时间内看到它们
These trails aren't really clouds, even though they look like it
这些痕迹并不是真正的云，尽管它们看起来像云
But jet trails and clouds are made mostly of the same stuff
但飞机留下的痕迹和云朵大多是由同样的物质构成的
Do you know what clouds are made of?
你知道云是由什么构成的吗？
Right, Squeaks! Clouds are mostly made out of water, and so are the trails that come from airplanes
对，吱吱！云主要是由水构成的，飞机留下的痕迹也是如此
But where does the water in the trails come from?
但是飞机痕迹的水是从哪里来的呢？
Well, you might know that jets can fly really high and super fast because of their powerful engines
嗯，你可能知道喷气机可以飞得非常高和非常快，因为它们强大的引擎
And just like most car engines need gas, jet engines need fuel to make them run
就像大多数汽车引擎需要汽油一样，喷气发动机也需要燃料才能运转
When engines burn fuel, they let out waste, which we call exhaust
当发动机燃烧燃料时，会产生废气，我们称之为废气
Jet exhaust is made of lots of things all mixed together, like little pieces of dirt, heat, and a type of water that we can't see because it's so spread out in the air, called water vapor
喷射式废气是由许多混合在一起的东西组成的，比如小块的灰尘、热量和一种我们看不见的水，因为它分散在空气中，叫做水蒸气
You know, you make a kind of exhaust, too — every time you breathe out!
你知道，你也会做一种排气——每次你呼气的时候!
It's not the same as jet exhaust, but it has does have some of the same things in it, like heat and vapor
它和喷气机排气不一样，但是它确实有一些相同的东西，比如热和蒸汽
If you put your hand close to your mouth…
如果你把手放在嘴边……
and breathe out on it gently
轻轻呼气
How does it feel?
感觉如何？
Warm, right?
温暖的，对吧?
You can feel /heat/ when you breathe out
你呼气时能感到热
But what about vapor?
但是蒸汽呢？
That's a little trickier because it's hard to see
这有点棘手，因为很难看到
But if you breathe out the same way, gently, on a mirror or window, you'll see that it gets foggy
但如果你以同样的方式呼气，轻轻地，在镜子或窗户上，你会看到雾气越来越浓
And that's how you know there's water vapor in your breath
这就是为什么你知道你的呼吸中有水蒸气
When the vapor in your warm breath touches the cooler window or mirror, it changes into teeny tiny droplets of water
当你呼出的热气接触到较冷的窗户或镜子时，它会变成极小的水滴
Together, all those little tiny droplets make the fog you see on the window or mirror
所有这些微小的液滴加在一起就形成了你在窗户或镜子上看到的雾
Now, you can't usually see the vapor that's in jet exhaust, either, just like you usually can't see your breath when you breathe out
现在，你通常也看不到喷气机排气中的蒸汽，就像你呼气时看不到你的呼吸一样
But you can see your breath sometimes, when it's cold!
但天气的冷的时候，有时你能看到自己的呼吸！
Right, Squeaks! When you breathe out on a cold day, the vapor in your breath changes into droplets of water, which is how you can see where you breathed out in the air
对，吱吱！当你在寒冷的天气呼出空气时，你呼出的蒸汽会变成水滴，这样你就能看见呼出的空气了。
The same kind of thing happens to the vapor coming from the plane
同样的事情也发生在来自飞机的蒸汽上
See, the higher you get up in the sky, the colder it gets
你看，你爬得越高，天就越冷
And jet planes fly really, really high up, where it's super duper cold
喷气式飞机飞得非常非常高，那里非常冷
So, the cold air cools down the vapor in the jet exhaust, turning it into drops, or even tiny pieces of ice
所以，冷空气冷却了喷气机排气中的蒸汽，把它变成水滴，甚至是微小的冰块
Tons of these little drops of water and ice make the trail that we see in the sky!
成吨的水滴和冰形成了我们在天空中看到的痕迹!
You might notice that some plane trails are wide and some are thin
你可能会注意到有些飞机痕迹很宽，有些很薄
Some last a long time and some disappear pretty quickly
有些持续很长时间，有些很快就消失了
All of these things depend mostly on how much vapor there is in the jet's exhaust, and how high the jet is flying
所有这些主要取决于喷气机的废气中有多少蒸汽，以及喷气机飞行的高度
Good question, Squeaks!
好问题，吱吱！
It's true that you won't always see a trail behind a plane
的确，你不会总是看到飞机后面的痕迹
If you see a plane without a trail, it might not be cold enough for the vapor to turn into water droplets or ice
如果你看到一架没有尾迹的飞机，它的温度可能不足以使水蒸气变成水滴或冰
And sometimes it just depends on the kind of engine that the plane has
有时候这取决于飞机的引擎
But if you do see one
但如果你看到了
now you know why! Come on, Squeaks, let's go look for more cloud shapes
现在你知道为什么了！来吧，吱吱，让我们去寻找更多的云层形状
We can see if we can spot any more planes, too!
我们可以看看是否还能发现更多的飞机！
Thanks for joining us!
感谢收看
If you want to keep learning and having fun with Squeaks and me,
如果你想继续学习和享受我和吱吱的乐趣，
hit the subscribe button,
点击订阅按钮，
and don't forget to check us out on the YouTube Kids app
别忘了去YouTube儿童应用上去看我们
We'll see you next time, here at the Fort!
我们下次在堡垒见！
