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为什么火焰周围的烟雾会跟着你走?

Why Does Smoke Follow You Around a Fire?

Thanks to Brilliant for supporting this episode of SciShow.
感谢Brilliant对本期科学秀的支持
To take your STEM skills to the next level,
要想提高你的STEM技能
go to Brilliant.org/SciShow for 20% off an annual premium subscription!
请登录Brilliant.org/SciShow享受年度订阅八折优惠
[♪ INTRO]
[♪ 序曲]
Imagine: You’re having a good time around a fire when out of nowhere,
想象一下:你正围着一堆火玩得很开心
the smoke blows straight into your face.
不知从哪里冒出来的烟直接吹到你脸上
Naturally, you just get up, you move to get out of the way.
你会本能地站起来 躲到一边
You go back to having a good time again,
然后回去继续玩
and the smoke is suddenly blowing right back in your face!
这烟又径直朝你脸上吹过来
It was over there when I was over there!
我躲这里 它就跟到这里
Now I’m over here, it’s over here!
我躲那里 它就跟到那里
You and the people near you, you move out of the way, everything’s fine for a bit.
你和边上的人让开了 一切又正常了起来
Until, once again, your eyes start to sting.
直到 你的眼睛再次开始刺痛
Eventually, everyone gets huddled in the one place
最后 大家都挤在了一个
that seems like it’s been smoke free.
似乎没有烟的地方
But you know what happens next.
但谁知道接下来还会发生什么呢
Your friends say that you are cursed
你朋友说你被诅咒了
because you brought the smoke with you as you moved.
因为烟都跟着你走
There is no curse, which is honestly too bad.
没有诅咒啦 说真的 这更糟
Because curses can be broken, but laws of physics cannot.
因为诅咒可以被打破 而物理法则不能
So all that smoke starts with fire.
烟因火而生
And fires release a lot of energy as heat,
火会以热的形式释放大量的能量
and air molecules nearby absorb some of that heat and start to move faster.
周围的气体分子吸收热量 开始加速移动
Since temperature is just an average measurement of how much
温度恰好是一个衡量分子能量的一般参数
energy molecules have, that means the air starts heating up too.
这就意味着空气也在开始升温
Those speedy molecules collide with their slower neighbors
那些高速运动的分子与周围速度较慢的分子碰撞
and send those neighbors flying off in the opposite direction,
让它们朝相反的方向飞去
freeing up space for the hot air near the fire to expand.
以腾出空间让火焰附近的热空气进行膨胀
This whole chain of events results in the air near the fire
这一连串的事件 导致火焰附近空气的密度
becoming less dense than the air around it.
比周围空气的密度小
Now, you may have heard that less-dense air rises, and that is true.
你该听过密度小的空气会上升 这是真的
It’s usually better to live on the top floor in the winter
一般来说 想要冬天暖和就住顶楼
and in the basement in the summer.
想要夏天凉快就住地下室
You also may have heard that less-dense air rises
你或许也听说密度小的空气上升
because it weighs less than the air it replaces,
是因为它比所取代的空气轻
which is also true, but it’s more of a definition than an explanation.
这也没错 但这更像是定义而不是解释
It just means that less-dense air rises because it’s less dense.
其实低密度空气上升就是因为它的密度小
The reason dense stuff sinks is because as you get
密度大的物质下沉的原因是
farther above the ground, there is less and less air above you.
离地面越远 其上方的空气越少
So air down at the ground has to push with a lot of force
所以地面上的空气必须用很大的力来支撑
to support the weight of all the air above it.
上面所有空气的重量
And it’s not just air!
不仅是空气!
Everything down here at the ground pushes against the weight of the air above it.
地面上所有物体都要承受其上方空气重量
Now, if you were light enough that the force of gravity on your body pulled you
现在 如果你足够轻 向下拉身体的重力
down less than that air pushed you up, you would lift off like a hot air balloon.
比空气的浮力小 你会像热气球一样上升
But you’re not: gravity pulls you down more than the air pushes you up.
但你并不轻 往下拉你的重力大于空气浮力
So you sink.
你会下沉
The hot air around a fire, on the other hand, is less dense than the air around it.
另一方面 火焰周围的热空气比其它的密度小
Gravity pulls it down less than the air around it pushes it up,
拉它的重力比周围空气托它的浮力小
and it rises into the sky.
所以它就升上天空了
This is called convection. It happens in the Sun; it happens in the Earth;
这就叫对流 太阳上 地球上都有这种现象
it happens in your oven, whether or not you have a convection oven.
你家烤炉也会有 不管是不是对流烤炉
And, most importantly, it happens around a fire.
最重要的是 对流也发生在火焰周围
And the real key to understanding why smoke keeps blowing in your face is that
而烟不断吹到你脸上的关键原因是
the rising air doesn’t just rise on its own.
上升的空气并不是自己在上升
It is pushed by the air around it.
它是在周围的空气推动下上升的
Because when hot air moves away from the fire, the air that pushed it
当热空气远离火焰时 推动它的空气就会
keeps right on going and fills the gap that the hot air left behind.
继续前进 填补热空气留下的空隙
And this is where you come in.
这就到你出场的时候了
You might think that you’re just sitting by the fire roasting some marshmallows.
你可能认为你只是坐在火边烤棉花糖
The fire is affecting you, but you’re not affecting the fire.
火在影响你 但你没有影响火
But you are.
其实并不然
You form a wall that creates a kind of vacuum.
你形成了一堵墙 制造了一种真空
If you were not there, air that comes from where you’re sitting
如果你不在那儿 你所坐地方的空气
and air that comes from across the fire would meet up at the fire and stop there.
和火堆对面来的空气会停在火堆处汇合 静止
But you are there, so your body blocks
但你在那儿 你的身体阻碍了
the air behind you from moving toward the fire.
身后的空气向火堆移动
So there’s nothing to stop the air coming toward you
所以 没有什么能阻止空气穿过火堆
from moving right on through the fire and into your face,
带着烟和燃烧的灰烬
bringing any smoke or soot from the fire along with it.
冲着你的脸扑上来
And since it’s you that’s blocking the air, you block the air wherever you move to.
因为你挡了空气 那么你跑到哪都会挡着
Even more annoyingly, the vacuum is stronger when you have
更糟的是 人越多 形成的真空就越强
more people in one place because more people block more of that airflow.
因为人越多 就会阻挡越多的气流
So you’re better off on your own than huddled with your friends
因此 如果你想避免让烟尘进入眼和肺部
if you want to avoid getting all that smoke in your eyes and lungs.
你最好一个人坐 不要和朋友挤在一起
Or you could just get rid of the smoke in the first place.
或者你一开始就避开烟
Then, the vacuum would just send warm air your way.
然后 真空会向你输送热空气
And that’s the idea behind smokeless fire pits.
这就是无烟炉背后的原理
Smoke is mostly compounds in wood that didn’t burn completely,
烟雾主要是木材中没有完全燃烧的化合物
either because the fire isn’t hot enough or because there isn’t enough oxygen.
产生的原因要么是温度不够高 要么是氧气不充足
Smokeless fire pits solve the second problem by creating additional paths for
无烟炉通过为进入的空气创造额外的路径
incoming air, reducing or even eliminating how much smoke a fire produces.
来解决氧气问题 减少甚至消除烟的产生
If that’s not an option, your next best bet is to bring a protractor.
如做不到 次之的选择是带个量角器
And the more protractors, the better the party.
量角器越多 派对越精彩
That’s what I always say.
我经常这么说
Without any outside wind, having everyone spaced out equally
在外面没有风的时候 每个人保持相等间隔
means that the same amount of air is blocked from all directions,
意味着从各个方向阻挡了等量的空气
and nobody’s vacuum is stronger than anyone else’s.
每个人身边都形成相同强度的真空
It’s really like a perfect pandemic activity: you’re outside,
这就像完美的大流行活动:你在外面
you’re breathing into a fire, plus, if you get too close to
你对着火呼吸 而且刚好你离你朋友很近
your friend, you get punished with a bunch of smoke in your eyes.
这么多烟 你的眼睛可就遭罪了
And if you’re looking for some more socially distant fun,
如你要找更多自娱自乐的内容
this video’s sponsor, Brilliant, has your back!
视频的赞助商 Brilliant 可以帮你实现
Brilliant is an online learning site with courses that you can complete
Brilliant是一个在线学习网站 你可以在他们的
all by yourself on their iOS or Android app.
iOS或Android app上完成所有课程
And they have a range of STEM topics
而且他们 有一系列的STEM主题
like their course on Gravitational Physics!
如他们的引力物理学课程
So if you liked this video about how things move around you, then maybe
如你喜欢这段物体如何在你周围运动的视频
you will enjoy learning about
那你也会想知道一个
different kinds of orbits an object can make.
物体如何形成的不同的轨道
In the Gravitational Physics course, you’ll start with the basics of what
在引力物理课程中 你将从质量的基本
mass even is and end up mastering Keplerian orbits.
概念开始 最终掌握开普勒轨道
Brilliant’s interactive course will walk you through thought experiments
Brilliant的互动课程将带领您完成思想实验
and give you a chance to work with real astronomical data.
并让您有机会使用真正的天文数据
So to join their community of learners and educators today,
来加入他们的学生和教师社区吧
click the link in the description down below or visit Brilliant.org/SciShow.
点击下方链接或访问 Brilliant.org/SciShow
You’ll get 20% off the annual Premium subscription by using that link.
通过这进入 你将获得年度订阅八折优惠
Thanks for watching!
感谢您的观看
[♪ OUTRO]
[♪ 结尾曲]

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视频概述

本视频通过生动的故事解释了火焰周围烟雾跟着人走的物理学原理。通过对空气对流原理的介绍引申出我们日常身边常见现象的理解。可以学以致用,非常有趣。

听录译者

收集自网络

翻译译者

Roger

审核员

审核员IBRT

视频来源

https://www.youtube.com/watch?v=WgxO7vhlF7A

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