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放屁带你去月球? – 译学馆
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放屁带你去月球?

Could You Fart Your Way to the Moon? | Space Time | PBS Digital Studios

【前奏播放】
[INTRO MUSIC PLAYING]
让我们开门见山
Let’s not beat around the bush.
你已经思考过这个问题了
You know you’ve thought about it,
今天 我们就来回答它
and today we’re going to answer it.
你能通过放屁去太空吗?
Could you fart your way through space?
【主题音乐播放】
[THEME MUSIC PLAYING]
如果太空服没能在你和外部环境之间
If space suits didn’t put a firm barrier
形成一个牢固的屏障
between you and the outside environment,
太空就会杀死你
space would kill you.
就这一期视频而言
But for the sake of this episode,
假如我们的生理机能超常
let’s take some biological license
并且假设你在没有太空服的情况下也能在太空生存
and pretend you could survive without a suit,
或者如果你喜欢 也可以假装
or if you prefer, pretend you have
你有一套带着特殊阀门的太空服
a suit with a special valve that would allow you to pass gas
它可以让你把气体排入真空的太空中
into the vacuum of space.
这样你就可以通过放屁推动自己前进了吗?
Could you then propel yourself with farts?
如果可以 这种方法能让你以多快的速度前进呢?
And if you could, how fast could they make you go?
在我们分析“放屁火箭”的概念之前
Before we can analyze the concept of a fart rocket,
我们需要分别了解
we need to understand the mechanics of those two
屁和火箭这两种材料的原理
ingredients separately, farts and rockets.
先来看看火箭吧 事实上
Let’s start with rockets, actually,
由于常见的误解
because there’s a common misconception
所以我想要先澄清一下
I want to clear up from the start.
火箭不是非要点燃或燃烧燃料
Rockets do not have to ignite or burn fuel
去推动其移动
in order to achieve propulsion.
以下这个例子可以帮助解释这一原理
An analogy will help explain this.
想像一下 你站在滑板上并且手里拿着
Imagine standing on a skateboard holding something
很重的东西 比如一个保龄球
really heavy, like a bowling ball.
在这样的场景中 你就代表着火箭 而保龄球
In this picture, you represent the rocket and the ball
就代表着燃料
represents the fuel.
此时你朝前猛推这个球
Now if you push the ball forward hard,
同样地 球也会向后推你
the ball also pushes backward on you,
在这个进程中 给你及滑板一个
giving you and the skateboard a backward
向后的速度
velocity in the process.
从根本上来说 这就是火箭的推进原理
Fundamentally, that’s how a rocket works.
当它在一个方向喷射燃料时
As it throws fuel in one direction,
燃料反过来也会推动火箭
the fuel pushes back on the rocket
朝着相反的方向运动
to accelerate in the opposite direction.
但不像我 火箭是没有手臂的
But unlike me, a rocket has no arms.
所以它是怎样投掷燃料的呢?
So how does it throw the fuel?
这个嘛 在传统火箭中
Well, in conventional rockets, that’s
这要用到点火装置
where the ignition comes in.
随着火箭燃料的氧化
As the rocket’s propellant oxidizes,
释放出化学键能量
chemical bond energy is released,
提高了它的温度
raising its temperature and causing
使它膨胀直到变成在燃烧室壁内反弹的
it to expand until it becomes a gas of particles bouncing off
气体粒子
the walls of the combustion chamber.
气体粒子总是均等地撞向四周的侧壁
Particles strike the lateral sides equally often,
因此可以说任何一侧都未受到推力
so there’s no net push sideways.
但沿着纵向轴线
But along the longitudinal axis, there’s
只有一面能撞击 这些粒子
only one wall to strike, and the particles
在向前撞击时 会推动火箭向前
push the rocket forward as they ricochet
然后从开放的一端逃出
and escape out the open end.
但假如火箭有手臂的话
But if rockets did have arms, they
他们可以像简单的投掷棒球一样来获得推进力
could just as easily use baseballs as propellant
而不需点燃任何东西
without igniting anything.
如果你将700万个克隆的邦加纳放入火箭
If you attached seven million clones of Madison Bumgarner
并且每个克隆的邦格纳 每秒从火箭中扔出一个
to a rocket and each clone threw one 90 mile an hour
每小时90英里的快球
fastball out of the rocket every second,
你就会获得
you would achieve the same thrust
跟史上最有强大的火箭一样的推动力
as the most powerful rocket ever built,
美国航天局最近在犹他州对SLS助推器进行了测试
the SLS Booster that NASA recently test fired in Utah.
(所以想要获得足够的推力)你只需足够快地投掷充足的量
So long as you throw enough mass sufficiently fast,
至于你扔是什么 则无关紧要
it doesn’t really matter what you’re throwing.
那这一切与放屁有什么关系呢?
So what’s all this have to do with farts?
好好想一想
Well, think about it.
放屁只是把气体排出体外
Flatulence is just throwing gas, as opposed
并不像是棒球或火箭燃料
to baseballs or rocket fuel, out of your body.
很显然 它产生的推力很小
Clearly, the resulting thrust is tiny enough
不足够使你在地表有明显的移动
not to move you noticeably here on Earth.
这就是为什么你没有在塔克贝尔
That’s why you don’t see patrons at Taco Bell achieving
看见顾客飞起来
lift off.
在太空站也是如此
The same is true inside the space station.
著名的加拿大宇航员克里斯在Reddit上透露
Famed Canadian astronaut Chris Hadfield revealed on Reddit
他在国际空间站亲身试验
that he had performed his own poot-pulsion experiments
发现并没有明显的移动
on the ISS with no noticeable movement.
但在太空近真空的条件下
But in the near total vacuum of space,
气体的排放肯定会使你移动的
expelling gas would have to make you move.
事实上 一天屁的量
In fact, with just a single day’s worth of flatus,
可以使你在30万年内
you could travel the entire Earth-Moon distance
完成从地球到月球的旅程
in only 300,000 years.
当然 这是在没有重力的情况下
And that’s only if there were no gravity.
事实上 即使从近地轨道推进
In truth, even starting out from low Earth orbit,
由于大量因素的影响
you’d be short of Earth’s escape velocity
你的逃逸速度也会减缓
by a factor of about a billion.
所以你几乎马上就会倒转
So you’d reverse course almost immediately.
那么“放屁火箭”不可行的根因是什么呢?
What’s the root cause of this fart rocket fail?
动量守恒定律
Conservation of momentum.
推动后 你及燃料的总动量
After a propulsion event, the net momentum
应保持为零
of you and your fuel must remain zero.
所以前冲力的动量应与
So your forward momentum must be equal and opposite
反向力的动量相等
to the backward momentum of the gas you expel.
那是究竟是多少动量呢?
So how much momentum is that?
让我们先从屁的排放速度讲起
Let’s start with the exhaust velocity of a fart.
【放屁的声音】
[FART NOISE]
我是位科学家 因此我更喜欢
I’m a scientist, so I would prefer
直接用风速仪来测量
to measure this directly using the wind speed fan.
但我一个都没有 因此我
But I couldn’t get one, so I used
用在网上看到的 每秒三米的量来
the 3 meters per second value I kept seeing on the internet.
估算出其所含的量
Estimating the mass is more involved.
你可以点击此处 查看我称量屁的方法
You can click over here to see my method of weighing farts.
我发现 即使是二十四多个小时
My result was that even over a full 24 hours,
平均每人仅仅产生约一克的屁
an average person produces around one measly gram
反冲速度仅仅在
of flatus, and that recoil speed ends up being a staggering 43
每秒43微米左右
microns per second.
那就是每小时15厘米 每天3.7米
That’s 15 centimeters an hour, 3.7 meters per day,
每周26米 每年1.3公里
26 meters in a week, or 1.3 kilometers per year.
结果呢?
Bottom line?
切奶酪并不会
Cutting the cheese just won’t cut it
开始长距离的太空旅途
for long distance space travel.
简单来说 就是气体的量不够
There’s simply not enough mass in your gas.
但或许你太空旅行的目标不那么大
But maybe your space travel goals are more modest.
让我们想想不同的情景
Let’s take a different scenario.
假设你被困于
Suppose you were stranded at rest
国际空间站 远离气锁门10米外的地方
10 meters away from the air lock door on the ISS.
你是否能够通过放屁把自己带到安全区域?
Could you fart your way to safety?
当然 你可能会需要两天半
Sure, over a period of about two and a half days,
或者三天半 如果你确实花费了24小时
or three and a half if you actually took a full 24
去堆积起一克的屁 并释放出来
hours to build up and release that one gram of gas,
在这小小的爆发中 使放屁速度达到最大
flatulating yourself to top speed in small bursts.
你可能会好奇 打喷嚏是否会有相同的结果
And in case you’re wondering, sneezing would probably have
打喷嚏所含的量以及喷发的速度
a similar result. The masses and exit speeds
与放屁是差不多的
of sneezes and farts should be comparable.
我了解到 网上的说法是 喷嚏每小时行驶100英里
I know the internet says sneezes travel at 100 miles an hour,
但一项与此有关的实验
but a study that we linked to in the description
运用高速摄影的方式
used high speed photography to get
显示打喷嚏的速度接近每秒4米
an answer closer to 4 meters per second,
跟我估算的放屁的速度差不多
right around my estimate for the speed of a fart.
在我们比较身体机能时
While we’re comparing bodily functions,
也许通过撒尿到达会比较安全
what about peeing your way to safety?
让我们计算下
Let’s do the math.
你可以通过抛射体运动学来
You can measure the exit speed of a urine stream using
测量尿流出的速度
projectile kinematics.
请参阅说明中的链接
See the link in the description.
我得出的结果是 尿流的速度也是每秒三到四米
Mine was in the same 3 to 4 meter per second range
我们看完了所有的情景
we’ve seen all episode.
既然尿液中主要包含的是水
Now, since urine is mostly water with the density
它的密度也差不多是1千克/公升 半公升尿液
of 1 kilogram per liter, the half liter
或者膀胱的容量
or so capacity of a full bladder would have a mass
是约五百克的量
of about half a kilogram.
这比一天放屁的量还高出500倍
That’s 500 times more than a day’s worth of gas.
那么这时动量守恒定律的结果会是?
So the net result for momentum conservation?
约500至700倍高的后坐力速度
About 500 to 700 times higher recoil velocity, a little
稍微超过每小时77米 这足够让你
over 77 meters per hour, or enough to get you
在八分钟内返回到国际空间站
back to the ISS in under eight minutes.
撒尿看上去似乎可行
So peeing looks like the way to go.
选取可与撒尿相比的放屁速度
To pick up comparable speed from farting,
你必须放响屁
you would have to literally break the sound barrier.
放屁的速度必须超过
The required exit velocity would exceed
每小时3000英里
Mach 4, over 3,000 miles per hour, which is over
它比SR-71黑鸟的最高速度还要快过50%
50% faster than the top speed of the SR-71 Blackbird,
很遗憾 没有任何喷嘴工程
and I’m sorry, but no amount of nozzle engineering
或者蓝色火焰计划
or blue flaming shenanigans will ever
能够让你达到那个速度 所以不要尝试
get you anywhere close to that, so don’t try it.
这个故事的寓意是?
Moral of the story?
如果你坚持朝一方移动 理论上
If you stick to moving sideways, can technically
你可以通过放屁到达太空 但撒尿更容易
fart your way through space, but you’re much better off peeing.
如果你始终坚持拿着七层卷饼
Or if you’re still holding on to the seven layer burrito
当作原料
you had planned to use as raw material,
还是算了吧
just throw it instead.
这个的反作用更大
You’ll get more recoil.
我希望 你们会觉得今天的这些分析是有帮助的
I hope you found today’s analysis informative.
欢迎你的评论与提问
Your comments and questions are welcome below.
如果 有人想知道有关排气速度的
And if anyone is aware of documentable measurements
可供参考的测量方法 也欢迎留言提问
of flatological exhaust speeds, include those too.
简单的说 学无止境
Let’s just say, inquiring minds want to know.
一如以往 我会在下期节目中
As always, I’ll report any findings
分享我的发现
on the next episode of ‘Space Time.’
上周我们讨论过《梅祖拉的假面》中的
Last week I considered whether the moon in Majora’s Mask
月球上是否存在着黑洞
might harbor a black hole.
你们有许多看法
You guys had a lot to say, and we’ll
我知道马上就会收到你们的评论
get your comments in a second.
但再提前通知一下
But first, an encore announcement.
本周末 4月11日和12日
This weekend, April 11 and 12, I’ll
我将在纽约市的主舞台上
be hosting NASA’s Space Apps Challenge at the Main
主持NASA太空应用挑战赛
Stage in New York City.
你可以在线参与或者现场参与
You can attend in person at various cities
世界各地城市的比赛
across the world or virtually online.
查看spaceappschallenge.org这个网站
Check out spaceappschallenge.org.
现在是提问时间
Now to your questions.
科斯莫斯问道 万有引力是否是
The Cosmos asked whether gravitational forces
引力场源的质量或密度
are about the mass or density of the gravitational source.
我的回答是 一旦你离开引力源
Answer– once you’re outside the gravitating
这时质量就起绝对作用
object, what matters is mass.
但另一天体能够在其被
But how close another object can get before it’s ripped apart
潮汐力分解前 能够距离天体多近
by the tidal forces due to a first object, which
这是引力差异造成的
is due to gravitational differentials,
事实证明它取决于第二个天体的密度
that turns out to depend on the density of that second object.
可在维基百科上查询洛希极限
Look up Roche limit on Wikipedia.
明华 诺亚 鲁姆 加雷斯以及帕里斯
R MH, Noah Fence, Fat Lum, Gareth Dean,
都问了类似的一个问题
and Parrish Danforth all asked in one way or another
为什么月球的表面没有坍塌
why the shell of the moon wouldn’t collapse and get
并被吸入黑洞
sucked into the black hole.
最简单的答案就是 黑洞不会吸
The short answer is that black holes don’t suck.
事实上 月球远远超过黑洞的视域
In fact, far from their horizon, which in this case
月球与黑洞的距离是厘米级的
would be just centimeters since the horizon is
而黑洞的视域是亚毫米级的 在这样的情况下
sub-millimeter sized, the fact that there’s
黑洞是否存在是没有关系的
a black hole in play becomes kind of irrelevant.
如果材料足够牢固
If you have material that’s strong enough
可以承受内部压力
to withstand internal stresses, you
你几乎可以把壳放在任何地方
could put a shell that just sits there
包括黑洞
around pretty much anything, including a black hole.
Chronoflect问道 在这个游戏中
Chronoflect asked whether Termina’s moon could actually
月亮是否真的会在三天内破碎
rip apart in the three day window of the game
如果它与月球的密度一样
if it were the density of Earth’s moon.
事实证明 分解的时间与受影响的时间
It turns out that time to disassembly
是一个非常棘手的问题
versus time to impact is a pretty tricky issue.
这个游戏中有很多因素
A lot of factors come into play.
我看过有关1994年苏梅克彗星
I’ve seen this modelled in the case
撞上木星的模拟场景
of the Shoemaker-Levy comet that hit Jupiter in 1994,
但我记不清是否有明确的规划
but I don’t recall whether there’s a definitive recipe.
我认为这取决于场景下的许多细节
I think it depends a lot on the details of the situation.
拉斐尔和丹尼尔问道
Raphael Hviding and Daniel Jenkins
黑洞是不是像我说的那样小?
asked, wouldn’t a black hole as small as the one I’m claiming
很快就消失了
evaporate quickly?
相对而言 是的
In relative terms, yes.
但这仍然需要当前的宇宙
But it would still take ten thousand trillion trillion
花费亿万年的时间
times the current age of the universe to do so.
最后 帕特里克·法根问道
Finally, Patrick Fadgen asked, how can the moon be
为什么游戏里一整天都能看到月亮
seen all day long from Termina?
这似乎需要月亮在行星轨道上的运转速度
You’d seem to need the moon to orbit around
与行星在其轴上旋转的速度相同
the planet at the same rate that the planet spins
我认为这种事情
on its axis, which I agree is not something
不应该会发生 如果月亮
that should happen if the moon is also gradually getting
离得越来越近
closer.
这是游戏的一大失误 正如我说的
It’s a major inaccuracy in the game, and as I said,
我并不知道所有的答案
I don’t have all the answers.
感谢所有的提问
Thanks for all the great questions.
继续啊 下次再见
Keep it up, and I’ll see you guys next time.
【主题音乐播放】
[THEME MUSIC]

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视频概述

放屁能带你去地球吗?如果可以,打喷嚏呢?撒尿呢?我们一起来看看吧

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视频来源

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