如果把大象从摩天大楼上扔下去会发生什么？生命与体型 1：英语精读讲义

Let's start this video by throwing a mouse, 表達脈絡

让我们在视频一开始先扔一只老鼠，

a dog,

一只狗，

and an elephant from a skyscraper onto something soft.

和一头大象，从摩天大楼上扔到柔软的东西上。

Let's say a stack of mattresses. 表達脈絡

假设是一堆床垫吧。

The mouse lands and is stunned for a moment

老鼠落地后先是懵了一会儿，

before it shakes itself off and walks away 短語動詞

然后抖了抖身子走开了，

pretty annoyed 用詞

并且非常生气，

because that's a very rude thing to do.

因为这真是一件很粗鲁的事。

The dog breaks all of its bones

狗全身骨折，

and dies in an un-spectacular way,

死状平平，

and the elephant explodes into a red puddle of bones and insides

而大象则爆炸成了一滩由骨头和内脏组成的红色血水，

and has no chance to be annoyed.

连生气的机会都没有。

Why does the mouse survive,

为什么老鼠活下来了，

but the elephant and dog don't?

而大象和狗却死了？

The answer is size.

答案是体型。

Size is the most under-appreciated regulator of living things. 用詞

体型是生物界中最被低估的调节因素。

Size determines everything about our biology,

体型决定了我们生物学的一切，

how we're built,

我们的身体构造，

how we experience the world,

我们如何体验这个世界，

how we live and die.

以及我们如何生存和死亡。

It does so because the physical laws are different for different sized animals.

它是如此重要的原因在于，物理定律对不同体型的动物是不同的。

Life spans seven orders of magnitude 用詞

生命的跨度横跨七个数量级，

from invisible bacteria to mites,

从隐形的细菌到螨虫，

ants, mice, dogs, humans,

蚂蚁、老鼠、狗、人类，

elephants, and blue whales.

还有大象和蓝鲸。

Every size lives in its own unique universe 習語

每种体型的生物都生活在各自独特的宇宙中，

right next to each other,

它们比邻而居，

each with its own rules,

每个宇宙都有着自己的规则，

upsides and downsides. 短語搭配

以及各自的优缺点。

We'll explore these different worlds in a series of videos.

我们将通过一系列视频探索这些不同的世界。

Let's get back to the initial question. 表達脈絡

让我们回到最初的问题。

Why did our mouse survive the fall?

为什么我们的老鼠在坠落中幸存下来了？

Because of how scaling size changes everything,

因为体型比例的缩放改变了一切，

a principle that we'll meet over and over again.

这是一个我们将会一再遇到的原理。

Very small things,

非常小的东西，

for example,

举个例子，

are practically immune to falling from great heights

对高处坠落几乎免疫，

because the smaller you are, 語法

因为你的体型越小，

the less you care about the effect of gravity.

就越不用在乎重力的影响。

Imagine a theoretical spherical animal the size of a marble.

想象一个理论上的球形动物，大小像一颗玻璃弹珠。

It has three features:

它具有三个特征：

its length,

它的长度，

its surface area which is covered in skin,

覆盖皮肤的表面积，

and its volume or all the stuff inside it

以及它的体积或者说是里面的所有东西，

like organs, muscles, hopes and dreams.

比如器官、肌肉、希望和梦想。

If we make it 10 times longer,

如果我们把它变长10倍，

say the size of a basketball,

假设变成篮球那么大，

the rest of its features don't just grow 10 times.

它的其他特征可不仅仅是跟着增长10倍。

Its skin will grow 100 times and its insides

它的皮肤会增长100倍，而它的内脏，

or its volume grows by 1,000 times.

或者说它的体积会增加1000倍。

The volume determines the weight or more accurately mass of the animal. 表達脈絡

体积决定了动物的重量，或者更准确地说是质量。

The more mass you have,

质量越大，

the higher your kinetic energy before you hit the ground,

你在撞击地面之前的动能就越高，

and the stronger the impact shock.

撞击的冲击力也就越强。

The more surface area in relation to your volume or mass you have, 短語搭配

你的表面积相对于体积或质量越大，

the more the impact gets distributed and softened,

冲击力就越能被分散和缓冲，

and also the more air resistance will slow you down.

并且空气阻力也能更好地让你减速。

An elephant is so big that it has extremely little surface area in ratio to its volume,

大象实在太大了，所以它的表面积与体积的比值非常小，

so a lot of kinetic energy gets distributed over a small space

这意味着巨大的动能集中在很小的区域上，

and the air doesn't slow it down much at all.

而且空气几乎无法让它减速。

That's why it's completely destroyed in an impressive explosion of goo when it hits the ground.

这就是为什么它砸到地面时会变成一场惊人而粘稠的爆炸并被完全毁灭。

The other extreme, 表達脈絡

另一个极端是，

insects, have a huge surface area in relation to their tiny mass,

昆虫的表面积相对于它们微小的质量来说是巨大的，

so you can literally throw an ant from an airplane

所以你完全可以把一只蚂蚁从飞机上扔下去，

and it will not be seriously harmed.

它也不会受重伤。

But while falling is irrelevant in the small world, 表達脈絡

但是，虽然坠落在这个微小世界里无足轻重，

there are other forces that are harmless for us,

却有其他一些对我们来说毫无危险的力，

but extremely dangerous for small beings.

对小生物而言极其致命。

Like surface tension,

比如表面张力，

which turns water into a potentially deadly substance for insects.

它把水变成了对昆虫来说潜在的致命物质。

How does it work?

它是如何运作的？

Water has the tendency to stick to itself. 短語搭配

水有粘在一起的倾向。

Its molecules are attracted to each other through a force called cohesion, 講解

它的分子通过一种被称为内聚力的力量相互吸引，

which creates a tension on its surface that you can imagine as a sort of invisible skin. 習語

这在水的表面产生了一种张力，你可以把它想象成一种看不见的皮肤。

For us, this skin is so weak that we don't even notice it normally. 語法

对于我们来说，这种皮肤太微弱了，通常我们甚至注意不到。

If you get wet,

如果你弄湿了，

about 800 g of water or about 1% of your body weight sticks to you.

大概有800克的水，也就是你体重的1%会粘在你身上。

A wet mouse has about 3 g of water sticking to it,

一只湿透的老鼠大约会有3克水粘在身上，

which is more than 10% of its body weight.

这超过了它体重的10%。

Imagine having eight full water bottles sticking to you when you leave the shower. 表達脈絡

想象一下你洗完澡出来时身上挂着八满瓶水的感觉。

But for an insect,

但对昆虫来说，

the force of water's surface tension is so strong that getting wet is a question of life and death. 習語

水的表面张力是如此之强，以至于被弄湿是个生死攸关的问题。

If we were to shrink you to the size of an ant and you touch water, 語法

如果我们把你缩小到蚂蚁大小，然后你碰到水，

it would be like you were reaching into glue.

那感觉就像你伸进了胶水里。

It would quickly engulf you,

它可以迅速吞噬你，

its surface tension too hard for you to break, 語法

它的表面张力大到你无法打破，

and you drown.

然后你就会被淹死。

So insects evolved to be water repellent. 用詞

因此，昆虫进化出了疏水的特性。

For one, 表達脈絡

一方面，

their exoskeleton is covered with a thin layer of wax, 短語搭配

它们的外骨骼上覆盖着一层薄薄的蜡，

just like a car.

就像汽车一样。

This makes their surface at least partly water repellent because it can't stick to it very well.

这使得它们的表面至少有部分是防水的，因为水很难附着在上面。

Many insects are also covered with tiny hairs that serve as a barrier. 短語搭配

许多昆虫身上还覆盖着细小的绒毛，作为一道屏障。

They vastly increase their surface area and prevent the droplets from touching their exoskeleton 語法

它们极大地增加了表面积，阻止水滴接触到外骨骼，

and make it easier to get rid of droplets. 短語動詞

同时也使得甩掉水滴变得更容易。

To make use of surface tension, 短語搭配

为了利用表面张力，

evolution cracked nanotechnology billions of years before us. 習語

进化在人类出现前的数十亿年就已经破解了纳米技术。

Some insects have evolved a surface covered by a short and extremely dense coat of water-repelling hair.

有些昆虫进化出了覆盖有短且极其浓密的拒水毛发的表面。

Some have more than a million hairs per square millimeter.

有些每平方毫米有多达一百多万根毛发。

When the insect dives underwater,

当昆虫潜入水中时，

air stays inside their fur and forms a coat of air.

空气会留在它们的皮毛里，形成一件空气外套。

Water can't enter because the hairs are too tiny to break its surface tension.

水进不去，因为这些毛发太细小，无法打破水的表面张力。

But it gets even better. 表達脈絡

但更绝的还在后头。

As the oxygen of the air bubble runs out, 短語動詞

当气泡里的氧气耗尽时，

new oxygen diffuses into the bubble from the water around it 用詞

新的氧气会从周围的水中扩散进气泡，

while the carbon dioxide diffuses outwards into the water.

同时二氧化碳会向外扩散到水中。

And so the insect carries its own outside lung around

因此，这只昆虫随身带着自己外部的肺，

and can basically breathe underwater thanks to surface tension. 短語搭配

而且多亏了表面张力，基本上能在水下呼吸。

This is the same principle that enables pond skaters to walk on water,

这就是让水黾能在水面上行走的原理，

by the way. 表達脈絡

顺带一提。

Tiny anti-water hairs.

微小的抗水毛发。

The smaller you get,

你的体型越小，

the weirder the environment becomes.

所处的环境就越怪异。

At some point, even air becomes more and more solid. 語法

在某种程度上，连空气也会变得越来越固态。

Let's now zoom down to the smallest insects known, 表達脈絡

现在让我们把镜头对准已知最小的昆虫，

about half the size of a grain of salt,

大概只有盐粒的一半大小，

only 0.15 mm long,

只有0.15毫米长，

the fairyfly.

缨小蜂。

They live in a world even weirder than other insects.

它们生活在一个比其他昆虫更怪异的世界里。

For them,

对它们来说，

air itself is like thin Jell-O, 文化背景

空气本身就像稀薄的果冻，

a syrup-like mass surrounding them at all times. 用詞

一种糖浆状的物质无时无刻不在包围着它们。

Movement through it is not easy.

在其中移动并不容易。

Flying on this level is not like elegant gliding.

在这个层级飞行可不像是优雅的滑翔。

They have to kind of grab and hold on to air. 講解

它们必须想办法抓住并攀附在空气上。

So their wings look like big hairy arms rather than proper insect wings. 語法

所以它们的翅膀看起来像毛茸茸的大手，而不像正常的昆虫翅膀。

They literally swim through the air 習語

它们真的就像在空气中游泳一样，

like a tiny gross alien through syrup.

就像一个微小恶心的外星人在糖浆中穿梭。

Things only become stranger from here on 短語搭配

从这里开始，事情只会变得越来越奇怪，

as we explore more universes of different sizes.

随着我们探索更多不同尺度的宇宙。

The physical rules are so different for each size

每个体型的物理规则是如此不同，

that evolution had to engineer around them over and over 用詞

以至于在过去十亿年里，随着生命体型的增长，

as life grew in size in the last billion years.

进化不得不在这些规则周围一次又一次地重新设计。

So why are there no ants the size of horses? 表達脈絡

那么，为什么没有马一样大的蚂蚁呢？

Why no elephants the size of amoeba?

为什么没有变形虫一样大的大象呢？

Why?

为什么呢？

We'll discuss this in the next part.

我们会在下一部分讨论这个。

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我们现在有一份每月的电子快报。

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如果你不想错过新视频的话请订阅，

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