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What Happens If We Throw an Elephant From a Skyscraper? Life & Size 1

在视频的开头 我们将老鼠 狗和大象
Let’s start this video by throwing a mouse, a dog, and an elephant
from a skyscraper onto something soft.
比如说 一堆床垫
Let’s say, a stack of mattresses.
老鼠着陆后 被吓得愣了一会
The mouse lands and is stunned for a moment,
before it shakes itself off,
and walks away pretty annoyed,
because that’s a very rude thing to do.
The dog breaks all of its bones
and dies in an unspectacular way,
and the elephant explodes into a red puddle of bones and insides
and has no chance to be annoyed.
Why does the mouse survive,
but the elephant and dog don’t?
The answer is Size.
Size is the most underappreciated regulator of living things.
Size determines everything about our biology,
我们的构成 我们经历 以及我们生存模式和死法
how we are built, how we experience the world, how we live and die.
It does so because the physical laws are different for different sized animals.
生物跨越7个数量级 从看不见的细菌到螨虫 蚂蚁
Life spans seven orders of magnitude, from invisible bacteria to mites, ants,
老鼠 狗 人类 大象最后到蓝鲸
mice, dogs, humans, elephants and, blue whales.
Every size lives in its own unique universe right next to each other,
每个都有自己的规则 有好有坏
each with its own rules, upsides, and downsides.
We’ll explore these different worlds in a series of videos.
让我们回到最初的问题 为什么老鼠能在坠落里存活?
Let’s get back to the initial question: Why did our mouse survive the fall?
因为体型差异会让一切都迥然不同 这个道理我们还会多次提及
Because of how scaling size changes everything; a principle that we’ll meet over and over again.
举个例子 非常小的东西实际上对从高处掉落免疫
Very small things, for example, are practically immune to falling from great heights
because the smaller you are the less you care about the effect of gravity.
Imagine a theoretical spherical animal
跟弹珠那么大 它有3个属性 即长度 表面积
the size of a marble. It has three features: its length, its surface area,
(覆盖有皮肤的区域)还有体积或者里面的所有填充物 像是器官
(which is covered in skin) and its volume, or all the stuff inside it like organs,
肌肉 希望和梦想如果我们将它增长10倍 也就是说
muscles, hopes and dreams. If we make it ten times longer, say the size of a
变成篮球那么大 剩下的属性不止于增加10倍
basketball, the rest of its features don’t just grow ten times. Its skin will
它的外皮表面会增长100倍 而且它的内部(就是体积)增长过1000倍
grow 100 times and it’s inside (so it’s volume) grows by 1000 times.
体积决定重量 或者更准确的说 动物的质量你质量越大
The volume determines the weight, or more accurately, mass of the animal. The more mass you have,
你落地之前的动能就越大 冲击力就越强
the higher your kinetic energy before you hit the ground and the stronger the impact shock.
The more surface area in relation to your volume
或者说质量越大 分散缓和的冲击力就越大
or mass you have, the more the impact gets distributed and softened, and also
the more air resistance will slow you down.
大象太大了 以至于比起它的体积 表面积要小得多
An elephant is so big that it has extremely little surface area in ratio to its volume.
所以大量的动能分布在小区域内 且空气并不能让其减速
So a lot of kinetic energy gets distributed over a small space and the air doesn’t slow it down much at all.
这就是大象落地时 被完全摧毁成一堆肉泥的原因
That’s why it’s completely destroyed in an impressive explosion of goo when it hits the ground.
而其他极端的生物 昆虫
The other extreme, insects,
have a huge surface area in relation to their tiny mass
so you can literally throw an ant from an airplane
and it will not be seriously harmed. But while falling is irrelevant in the small
world there are other forces for the harmless for us but extremely dangerous for small beings.
像是表面张力 会使水变成对昆虫而言的潜在致命物质
Like surface tension which turns water into a potentially deadly substance for insects.
How does it work? Water has the tendency to stick to itself;
its molecules are attracted to each other through a force called cohesion
它能在表面造成一种张力 你可以把它想作成一种无形外皮
which creates a tension on its surface that you can imagine as a sort of invisible skin.
种外皮对我们来说太脆弱了 让我们经常忽略了它的存在
For us this skin is so weak that we don’t even notice it normally.
If you get wet about 800 grams of water or about one percent of your body weight sticks to you.
A wet mouse has about 3 grams of water sticking to it,
which is more than 10% of its body weight.
Imagine having eight full water bottle sticking to you when you leave the shower.
但是对于昆虫 水的表面张力很强
But for an insect the force of water surface tension is so strong
that getting wet is a question of life and death.
If we were to shrink you to the size of an ant
and you touch water it would be like you were reaching into glue. It
水会很快吞噬你 它的表面张力强到让你无法挣脱
would quickly engulf you, its surface tension too hard for you to break and
并且会溺水窒息 昆虫因此而进化出防水措施
you’d drown. So insects evolved to be water repellent.
它们的外骨骼包被一层蜡 就像车子一样
For one their exoskeleton is covered with a thin layer of wax just like a car.
这让它的表面至少能在一定程度上防水 因为它黏着性不好了
This makes their surface at least partly water repellent because it can’t stick to it very well.
Many insects are also covered with tiny hairs that serve as a barrier.
They vastly increase their surface area
and prevent the droplets from touching their exoskeleton
and make it easier to get rid of droplets.
To make use of surface tension
evolution cracked nanotechnology billions of years before us.
Some insects have evolved a surface covered by a short and extremely dense coat of water repelling hair.
Some have more than a million hairs per square millimeter when
当昆虫跳进水里时 它们皮毛内部保留有空气 形成了空气套
the insect dives under water air stays inside their fur and forms a coat of air.
水进不去 因为它们的防水毛很细小 不能打破它的表面张力
Water can’t enter it because their hairs are too tiny to break its surface tension.
但是更棒的是 当气泡中的空气耗尽时 新的空气
But it gets even better, as the oxygen of the air bubble runs out, new oxygen
散布进水周围的气泡里 而二氧化碳
diffuses into the bubble from the water around, it while the carbon dioxide
向外散布到水中 所以昆虫外置自己的肺
diffuses outwards into the water. And so the insect carries its own outside lung
around and can basically breathe underwater thanks to surface tension.
This is the same principle that enables pond skaters to walk on water by the way,
细小防水毛 你越小 你所存在的环境就越怪诞
tiny anti-water hairs. The smaller you get the weirder the environment becomes. At
在某个时间 空气也会变得越来越立体 让我们缩小
some point even air becomes more and more solid. Let’s now zoom down to the
到我们所知的最小昆虫吧 大约有一颗盐粒那么大
smallest insects known, about half the size of a grain of salt,
只有0.15毫米长:苍蝇仙子 它们生活的地方比
only 0.15 millimeters long: the Fairy Fly. They live in a world even weirder than
其他昆虫更加怪诞 对他们来说空气本身像薄薄的果冻 糖浆状物质
another insects. For them air itself is like thin jello, a syrup-like mass
一直环绕在周围 想要穿过它运动并不简单
surrounding them at all times. Movement through it is not easy. Flying
在这种水平的空气中飞行并不能很优雅 它们不得不夺取
on this level is not like elegant gliding; they have to kind of grab and
并紧紧抓住空气 所以它们的翅膀看起来就像毛茸茸的手臂 而不是昆虫合适的翅膀
hold onto air. So their wings look like big hairy arms rather than proper insect wings.
它们能随意在空气中游泳 就像糖浆里渺小的外星人
They literally swim through the air, like a tiny gross alien through syrup.
随着我们探索不同体型生物的多样性 事情至此变得越发奇怪了
Things only become stranger from here on as we explore more diversity of different sizes.
物理法则对于不同体型生物表现不同 生物周围有进化指导方向
The physical rules are so different for each size that evolution had to engineer around them
周而复始 且随着生物规模的增长有上十亿年了
over and over as life grew in size in the last billion years.
So why are there no ants the size of horses?
Why are no elephants the size of amoeba? Why?
We’ll discuss this in the next part.
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