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你、小狗、大象排尿的时间都是21秒 – 译学馆
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你、小狗、大象排尿的时间都是21秒

You, a Dog, and an Elephant All Pee for 21 Seconds

[开场音乐]
{ ♪INTRO }
哺乳动物 无论是猫 是人
Mammals, whether they be cats or people
还是角马 都有一些共同点
or wildebeests, have a few things in common
如你所知 比如毛发 哺乳…
you know, hair, milk…
还有 撒尿的时长是21秒
and peeing for 21 seconds.
确确实实是这样的!
This is an actual thing!
很多哺乳动物花21秒
Lots of mammals take about 21 seconds
来排空满满的膀胱
to empty their full bladder.
不论它们的膀胱含5毫升
It doesn’t matter if their bladder contains 5 milliliters
还是18升尿液
of urine or 18 liters.
21秒似乎是一个有魔力的数字
21 seconds seems to be the magic number.
这要归功于
And that’s thanks to a combination
生理学和流体动力学的珠联璧合
of physiology and fluid dynamics.
排泄所需时间取决于
The time it takes to tinkle depends on the amount
排泄总量与流速
you need to expel and the flow rate—
–你尿得有多快
how fast you expel it.
其中流速又取决于 比如说
That rate, in turn, depends on things like
尿道的直径
the width of your urethra— the pipe
尿道是将尿液从膀胱
that delivers urine from the bladder
输送到外界的管道 还有压出尿液的压强
to the outside world— and the pressure pushing the pee out.
现实中 这些管道
And it just so happens that those pipes
相对成比例 那就是 体型较大的动物
are fairly proportional: that is, the larger the animal,
拥有更长更宽的尿道
the longer and wider the urethra.
动物膀胱肌群产生的压强
The pressure created by an animal’s bladder muscles
具有显著的恒定性 就是5.2千帕 你想知道的话
is remarkably constant— about 5.2 kilopascals, if you were wondering.
记在脑子里了吧?
You know you have that number in your brain.
我很确定你会记得很久
I’m sure it’ll stay there for a long time.
但是 总的来说 排尿产生的压强
But the overall pressure pushing the urine out
也取决于尿液的流体静力学压强
also depends on both that and the urine’s
即流体本身展现的压强
hydrostatic pressure: the pressure exerted by the fluid itself.
假如你是头马
So if you’re a horse,
你的膀胱容量惊人
there’s a lot of weight in the bladder,
而所有内容物都在向下挤压
and all of that mass is pushing down
膀胱底部的尿液
on the urine at the bottom and
所以尿液就承受着与膀胱相同的压强
so it gets pushed the same amount by the bladder
但更多是来自流体静力学的压强
but much more by the hydrostatic pressure… …
然而假如你是一只猫 更少的尿液
whereas if you’re a cat you have less liquid
向下挤压底部尿液
pushing down on the liquid and
产生相同的膀胱压强
the same amount of bladder pressure
但是流体静压更低
but less hydrostatic pressure…
这一切都表明
All of that means that urine in a large
大型动物更有可能通过一条相对
animal is being pushed out more forcefully through a
更宽阔的尿管更有力地排尿
tube that’s proportionally wider… …
这导致尿速更快
that makes it flow more quickly,
从而弥补尿量上的差异
which makes up for any difference in volume.
我们知道以上这些 是因为已有的研究数据:
We know all this because some researchers actually did the math
一篇2014年
in a 2014 paper in
发表于美国国家科院会议的论文
Proceedings of the National Academy of Sciences.
他们也拍摄 观察了一群动物撒尿的过程
They also filmed and watched a bunch of animalspee
以验证他们的结论
to validate their results, which,
你懂的 这是科学
you know, that’s science!
虽然 这里也有一些相关说明
There are a few caveats, though.
21秒定理只适用于重量超过3千克的
The 21 second rule only counts for full bladders
哺乳动物
in mammals heavier than 3 kilograms.
对于那些小动物 像蝙蝠 大鼠和小鼠
For smaller animals like little bats, rats,or mice,
情况就会有所不同
something different happens.
它们排尿速度非常快
They urinate in a series of quick droplets
这是因为它们尿道细小
because the thinness of their urethras and
且流动的尿液产生的摩擦力
the friction created by the flowing fluid
通过抵消重力
actually pushes up on the liquid,
加速了排尿
opposing the force of gravity.
这会让尿液先是沾在尿道内壁上
This makes the urine droplets stick to the walls of the urethra at first,
并不断增大 直至重量足够被引力牵引 才能落地
and grow bigger in size until they’re heavy enough for gravity to take over. Then,
尿液落得很快 通常不到一秒
they fall out quickly— usually, in less than a second.
这可能也不适用于水生哺乳动物
It also might not apply to aquatic mammals
因为水 尤其是深处的水
because the water, especially at depth,
会对尿道施加压力 把尿液推回尿道
applies pressure to the urethra and pushes the pee back up the pipe.
至于游泳者也一样 在泳池里小便要花更长时间
The same goes for swimmers— it takes you longer to pee in the pool.
不是说你曾这么干过
Not that you’d ever do that. And,
要澄清的是 此说法不适用于爬行类和鸟类 因为它们的排泄系统全然不同
to be clear, none of this counts for reptiles or birds because they’ve got a whole different excretion system.
虽然研究动物排尿听起来有点···蠢
Now while this might sound kind of like…silly to study animal peeing,
了解尿液流动的数学物理知识实则很有实用价值
understanding the physics and mathematics of urine flow actually has some practical applications.
工程师可以把这些发现应用到设计系统
Engineers could apply these findings to design systems
这些系统里 水库 水塔 甚至不同大小的水背包
where reservoirs, water towers or even water backpacks of different sizes
都需要用同样的时间来清空
take the same amount of time to empty.
而且这也表明了研究小动物 如啮齿类的泌尿系统疾病
And this also suggests that studying urinary diseases in small animals like rodents
可能对人类并无帮助
might not be applicable to humans
因为即使具有相同的基本身体构造
because their whole peeing process is just fundamentally different than what we do…
排尿过程却根本不同
…even though we have the same basic body parts.
这说明了
It just goes to show
某些古怪的研究有时能带来有用的结果
that some curious research can sometimes lead to useful results.
感谢您观看本集科学秀
Thanks for watching this episode of SciShow!
此刻如果你正在想 这很棒但我想了解更多关于自己尿液的事情
Now If you’re here thinking. Well that was good but I want to know more about my pee,
啊 我们有一整集来谈论你的尿······
well, we have a whole episode on what your pee says about you….
[结尾音乐]
{ ♪OUTRO }

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视频概述

从哺乳动物尿尿中衍生的流体动力学

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视频来源

https://www.youtube.com/watch?v=R5lOGjHzNDU

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