美国各州按种族报告新冠肺炎确诊病例数据
黑人占全美人口13%但占新冠肺炎死亡人数的34%
这是美国系统性种族不平等现象的结果之一
这实在骇人听闻 无法接受 黑人的命也是命
《分钟物理》 N95口罩的天才工作原理
Prior to March 2020,
2020年3月之前
there’s a good chance you didn’t know what an N95 mask was,
你很可能还不知道N95口罩是什么
or at least didn’t think about them
至少没有真正了解过它们
unless you were doing a home repair project with lots of dust,
你可能只会在家庭装修项目弄的漫天灰尘
or live in a part of the world with crazy pollution or wildfire smoke.
或是生活在一个污染或山火严重的地方时想起它
And upon learning about them, you might think (like I did) that
在了解N95口罩的过程中 你可能和曾经的我一样
an N95 mask is basically a really really fine strainer:
认为它主要就是一张精细的滤网:
a mesh of fibers with gaps too small for dust and other airborne particles to get through.
一张缝隙极小的纤维网能够阻隔灰尘和大气颗粒物
A strainer filters out particles larger than its openings,
滤网会过滤掉直径大于其空隙的颗粒
but not particles smaller than its openings.
对直径小于其空隙的颗粒则无能为力
So with a mask you’d expect that after a certain point,
所以你会觉得当颗粒小到了一定程度后
small enough particles will sneak through.
它们就可以穿过口罩
But this isn’t how N95 masks work:
但N95口罩的工作原理并非如此:
the particles they filter are generally much smaller than the gaps between fibers in the mask!
一般来说 所过滤的颗粒比纤维之间的空隙小得多!
What’s more, an N95 mask is actually really good at filtering both the largest and smallest small particles
而且 N95口罩其实很擅长过滤大型和小型的颗粒
— it’s medium-sized small particles that are hardest for it to block.
中型的颗粒才是最难对付的
This isn’t at all like a strainer…
N95和过滤网大相径庭
because N95s are much cleverer than strainers.
因为它们比过滤网智能多了
The overarching goal of an N95 mask
一个N95口罩的首要任务
is instead to get an airborne particle to touch a fiber in the mask.
反而是让大气颗粒物接触口罩里的纤维
Regardless of how big an airborne particle is,
不论空气中有多大的颗粒
once it touches a fiber
一旦接触到了纤维
it stays stuck to it and doesn’t become airborne again.
它就会被纤维粘住 无法再回到空气中
This isn’t anything special about the fibers,
并不是因为纤维有特殊之处
but about the size of the particles.
而是由于颗粒物的大小
At a microscopic scale everything is sticky,
所有微观物质都具有粘性
because the weakly attractive force between molecules
分子间的吸引力尽管很弱
is more than strong enough to hold very very small things in place.
也足够将极小的粒子固定住
So you shouldn’t think of N95 masks like
因此不要将N95口罩视作
a fine window screen that keeps insects of a certain size out;
一张能防范一定大小的昆虫的纱窗
you should think of them more like a sticky spider web
它更像是一张有粘性的蜘蛛网
that can catch an insect of any size, as long as it touches a strand.
可以捕捉任何大小触碰到网的昆虫
And so N95 masks use a bunch of different clever physics and mechanical tricks
N95口罩使用了物理学和机械学方面的多重技巧
to get particles to touch their fibers.
来达到使颗粒落网的目的
First, many spiderwebs are better than one.
首先 蜘蛛网的数量越多越好
Unlike strainers, where stacking many identical ones doesn’t improve the filtering at all,
不同于同密度叠加无法增效的滤网
more layers of sticky fibers means more chances for particles to get stuck.
粘性纤维网的叠加数量与捕获概率是成正比的
And how likely particles are to hit or miss a fiber
而颗粒撞上纤维的概率
depends in large part on their size.
很大程度上取决于其大小
Airborne particles larger than a thousandth of a millimeter
直径大于1微米的气载颗粒
basically travel in straight lines, because of their inertia.
由于惯性作用 基本上沿直线运动
And because there are so many layers of fibers,
由于纤维层足够多
their straight line paths are essentially guaranteed to hit a fiber and stick.
直线前行的颗粒基本上都会撞上纤维
Airborne particles that are really really small are so light
而极小的颗粒因为太轻
that collisions with air molecules literally bounce them around,
会被空气分子撞得四处弹跳
so they move in a random zig-zag pattern known as Brownian motion.
因此做无规则运动 即“布朗运动”
This zig-zagging also makes it super likely that
无规则的运动路线
a particle will bump into a fiber and get stuck.
也提高了颗粒撞上纤维被粘住的概率
Particles of in-between sizes are the hardest to filter.
中型颗粒是最难过滤的
That’s because they don’t travel in straight lines,
因为他们既不做直线运动
and they also don’t bounce around randomly.
也不做随机的无规则运动
Instead, they’re carried along with the air as it flows around fibers,
反而会在空气经过纤维时 随其一起穿过去
meaning they’re likely to get carried past fibers
意味着它们很可能从纤维边流走
and sneak through even a mask with many layers.
即使多层纤维的口罩也难以将其过滤
But N95 masks have a final trick up their sleeve.
但N95口罩还有一个终极秘密武器
They can attract particles of all sizes to them using an electric field.
它还可以用电场来吸引各种颗粒
In the presence of an electric field
电场作用下
even neutral particles develop an internal electrical imbalance
中型颗粒也会因内部电荷不平衡
which attracts them to the source of the electric field.
被吸引到电场源头
This is why neutrally-charged styrofoam sticks to a cat
这就是为什么带中性电荷的泡沫塑料
whose fur has been charged with static electricity.
会粘在一只全身毛带静电的猫身上
But unlike a cat’s fur,
与猫毛不同的是
an N95 mask’s electric field isn’t just ordinary static electricity.
N95口罩的电场有的不仅仅是普通静电
Their fibers are like permanent magnets,
口罩里的纤维就像永磁体
but for electricity: electrets!
但对于电来说就像:驻极体!
Just like you can permanently magnetize a piece of iron
就像 把一块铁放在强磁场里
by putting it in a strong enough magnetic field,
能永久磁化它一样
you can ‘electretize’ a piece of plastic to give it a permanent electric field.
你可以用永久的电场来“电化”一块塑料
By electretizing the fibers in an N95 mask,
通过对N95口罩内的纤维进行电化
they gain a long-lasting ability to attract particles,
即可赋予它们持久吸引颗粒的能力
which means they capture about 10 times as many particles as regular fibers.
致使电化纤维的颗粒捕获数量是普通的10倍
And this is, after all, the point of an N95 mask:
毕竟N95口罩的使命便在于此:
to filter out particles from the air.
过滤掉空气中的颗粒物
And they do it cleverly
并且它们的方法很聪明
by taking advantage of the molecular scale stickiness of matter,
首先 利用了微观物质的粘性
using many layers of fibers that catch straight-moving large particles
使用多层纤维来捕获直线运动的大颗粒
as well as zig-zagging small particles,
与无规则运动的小颗粒
and having an electric field that attracts all particles.
并具有能吸引所有颗粒的电场
You get a mask, not a strainer,
你的口罩不是滤网
that’s really good at trapping both large and small airborne particles
它非常擅长捕获大型和小型颗粒
and does a reasonably good job at filtering out middle sized particles.
也能出色地阻隔中型颗粒
Precisely what fraction of those sneaky medium-sized particles get blocked
口罩名中的数字
gives you the number of the mask
就代表着它对中型颗粒的过滤比例
– if at least 95% of those particles are filtered out,
—如果95%的中型颗粒被过滤掉了
then the mask is rated N95.
那么口罩的等级就是N95
Ok, Caveats.
好了 接下来是注意事项
So N95 masks can be very effective.
我们已经知道N95的过滤效率很高了
But if you’re a healthcare worker wearing one of them,
但如果你是一名需要戴N95的医护人员
here are a few important things to look out for.
以下是一些重要的注意事项
事项 #1:口罩的贴合度极为重要
The biggest influence on the performance of an N95 mask
影响N95口罩防护效果的最大因素
isn’t actually the mask – it’s whether you wear it properly.
不是口罩本身 而是你的佩戴方式
If a mask isn’t fully sealed on your face,
如果口罩没有紧密贴合你的脸颊
air and particles you’re trying to filter can just bypass the filter entirely.
要过滤的空气和颗粒就可以轻易绕过口罩
事项 #2:颗粒大小固然重要 但不用担心新冠病毒
Dust, smoke, pollen, bacteria, and viruses all have different sizes,
灰尘 烟尘 花粉 细菌和病毒都有着不同的大小
and so are filtered by N95 masks to different extents.
因此它们被N95过滤的程度是不同的
However, germs for airborne illnesses don’t usually travel on their own –
然而 通过空气传播的疾病病菌通常不自行运动—
we breathe or cough them out in droplets which have a wide range of sizes.
它们藏在我们呼出或咳出的大小差异巨大的飞沫里
So the size of the virus or bacteria itself isn’t particularly relevant.
因此病毒或细菌本身的大小并不重要
事项 #3:消毒会损坏口罩
N95 masks are intended to be disposable,
N95是一次性口罩
but the demand from COVID-19 has led to a global shortage of N95 masks
但新冠病毒的肆虐造成了N95的供不应求
and the reality is that health workers have to reuse them –
现实所迫 医护人员就只能重复使用—
and thus decontaminate them.
所以会给口罩消毒
It’s important to be aware that certain kinds of decontamination
你需要知道的是 有些消毒方式
for example, using alcohol or liquids
例如 用酒精或一些液体消毒
can damage the electrostatic properties of a mask and destroy their filtering ability,
会对口罩的静电性能和过滤性能造成损害
even if the mask appears unaffected.
即使它表面上安然无恙
N95decon is a volunteer team of scientists
N95decon是一个科学家志愿者团队
developing and sharing research-based decontamination methods
他们研究并分享基于实验结果的消毒方法
so that masks can be reused during this crisis.
以便在疫情中 提高口罩的重复利用率
A big thanks to Brilliant for supporting this video –
非常感谢Brilliant对本视频的支持
in this time of social isolation and pandemic,
在社交孤立且疫情肆虐的时代
the value of being versed in math and science is particularly evident,
数学和科学技能越发重要
and Brilliant continues to be a place you can go to learn and play with mathematical and scientific ideas.
Brilliant依旧提供将数学和科学理念寓教于乐的平台
Just today I exchanged emails with a viewer
今天 我和一名观众互通邮件
who had a question about some special relativity calculations,
他对狭义相对论的一些计算有疑问
and I recommended that they check out Brilliant’s introductory course on special relativity –
然后我就推荐了Brilliant的狭义相对论入门课—
there’s no better way to learn than by directly engaging with questions & problems!
最为有效的学习方法就是带着疑问解决谜题!
Brilliant also has fun daily challenges on various math, logic, science & engineering topics.
数学 逻辑学 科学和工程学的每日趣味挑战也在Brilliant等着你
To learn more about Brilliant, go to brilliant.org/MinutePhysics and sign up for free;
想了解更多请免费登录brilliant.org/MinutePhysics;
the first 200 people will get 20% off an annual Premium subscription
前200人将得到一张年度会员八折优惠券
to all of Brilliant’s courses, quizzes, and puzzles.
解锁Brilliant所有的课程 测试与游戏
Thanks to Brilliant for supporting MinutePhysics.
感谢Brilliant对本频道的支持

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