[INTRO MUSIC PLAYING]
Let's not beat around the bush.
You know you've thought about it,
and today we're going to answer it.
Could you fart your way through space?
[THEME MUSIC PLAYING]
If space suits didn't put a firm barrier
between you and the outside environment,
space would kill you.
But for the sake of this episode,
let's take some biological license
and pretend you could survive without a suit,
or if you prefer, pretend you have
a suit with a special valve that would allow you to pass gas
into the vacuum of space.
Could you then propel yourself with farts?
And if you could, how fast could they make you go?
Before we can analyze the concept of a fart rocket,
we need to understand the mechanics of those two
ingredients separately, farts and rockets.
Let's start with rockets, actually,
because there's a common misconception
I want to clear up from the start.
Rockets do not have to ignite or burn fuel
in order to achieve propulsion.
An analogy will help explain this.
Imagine standing on a skateboard holding something
really heavy, like a bowling ball.
In this picture, you represent the rocket and the ball
represents the fuel.
Now if you push the ball forward hard,
the ball also pushes backward on you,
giving you and the skateboard a backward
velocity in the process.
Fundamentally, that's how a rocket works.
As it throws fuel in one direction,
the fuel pushes back on the rocket
to accelerate in the opposite direction.
But unlike me, a rocket has no arms.
So how does it throw the fuel?
Well, in conventional rockets, that's
where the ignition comes in.
As the rocket's propellant oxidizes,
chemical bond energy is released,
raising its temperature and causing
it to expand until it becomes a gas of particles bouncing off
the walls of the combustion chamber.
Particles strike the lateral sides equally often,
so there's no net push sideways.
But along the longitudinal axis, there's
only one wall to strike, and the particles
push the rocket forward as they ricochet
and escape out the open end.
But if rockets did have arms, they
could just as easily use baseballs as propellant
without igniting anything.
If you attached seven million clones of Madison Bumgarner
to a rocket and each clone threw one 90 mile an hour
fastball out of the rocket every second,
you would achieve the same thrust
as the most powerful rocket ever built,
the SLS Booster that NASA recently test fired in Utah.
So long as you throw enough mass sufficiently fast,
it doesn't really matter what you're throwing.
So what's all this have to do with farts?
Well, think about it.
Flatulence is just throwing gas, as opposed
to baseballs or rocket fuel, out of your body.
Clearly, the resulting thrust is tiny enough
not to move you noticeably here on Earth.
That's why you don't see patrons at Taco Bell achieving
lift off.
The same is true inside the space station.
Famed Canadian astronaut Chris Hadfield revealed on Reddit
that he had performed his own poot-pulsion experiments
on the ISS with no noticeable movement.
But in the near total vacuum of space,
expelling gas would have to make you move.
In fact, with just a single day's worth of flatus,
you could travel the entire Earth-Moon distance
in only 300,000 years.
And that's only if there were no gravity.
In truth, even starting out from low Earth order,
you'd be short of Earth's escape velocity
by a factor of about a billion.
So you'd reverse course almost immediately.
What's the root cause of this fart rocket fail?
Conservation of momentum.
After a propulsion event, the net momentum
of you and your fuel must remain zero.
So your forward momentum must be equal and opposite
to the backward momentum of the gas you expel.
So how much momentum is that?
Let's start with the exhaust velocity of a fart.
[FART NOISE]
I'm a scientist, so I would prefer
to measure this directly using the wind speed fan.
But I couldn't get one, so I used
the 3 meters per second value I kept seeing on the internet.
Estimating the mass is more involved.
You can click over here to see my method of weighing farts.
My result was that even over a full 24 hours,
an average person produces around one measly gram
of flatus, and that recoil speed ends up being a staggering 43
microns per second.
That's 15 centimeters an hour, 3.7 meters per day,
26 meters in a week, or 1.3 kilometers per year.
Bottom line?
Cutting the cheese just won't cut it
for long distance space travel.
There's simply not enough mass in your gas.
But maybe your space travel goals are more modest.
Let's take a different scenario.
Suppose you were stranded at rest
10 meters away from the air lock door on the ISS.
Could you fart your way to safety?
Sure, over a period of about two and a half days,
or three and a half if you actually took a full 24
hours to build up and release that one gram of gas,
flatulating yourself to top speed in small bursts.
And in case you're wondering, sneezing would probably have
a similar result. The masses and exit speeds
of sneezes and farts should be comparable.
I know the internet says sneezes travel at 100 miles an hour,
but a study that we linked to in the description
used high speed photography to get
an answer closer to 4 meters per second,
right around my estimate for the speed of a fart.
While we're comparing bodily functions,
what about peeing your way to safety?
Let's do the math.
You can measure the exit speed of a urine stream using
projectile kinematics.
See the link in the description.
Mine was in the same 3 to 4 meter per second range
we've seen all episode.
Now, since urine is mostly water with the density
of 1 kilogram per liter, the half liter
or so capacity of a full bladder would have a mass
of about half a kilogram.
That's 500 times more than a day's worth of gas.
So the net result for momentum conservation?
About 500 to 700 times higher recoil velocity, a little
over 77 meters per hour, or enough to get you
back to the ISS in under eight minutes.
So peeing looks like the way to go.
To pick up comparable speed from farting,
you would have to literally break the sound barrier.
The required exit velocity would exceed
Mach 4, over 3,000 miles per hour, which is over
50% faster than the top speed of the SR-71 Blackbird,
and I'm sorry, but no amount of nozzle engineering
or blue flaming shenanigans will ever
get you anywhere close to that, so don't try it.
Moral of the story?
If you stick to moving sideways, can technically
fart your way through space, but you're much better off peeing.
Or if you're still holding on to the seven layer burrito
you had planned to use as raw material,
just throw it instead.
You'll get more recoil.
I hope you found today's analysis informative.
Your comments and questions are welcome below.
And if anyone is aware of documentable measurements
of flatological exhaust speeds, include those too.
Let's just say, inquiring minds want to know.
As always, I'll report any findings
on the next episode of "Space Time."
Last week I considered whether the moon in Majora's Mask
might harbor a black hole.
You guys had a lot to say, and we'll
get your comments in a second.
But first, an encore announcement.
This weekend, April 11 and 12, I'll
be hosting NASA's Space Apps Challenge at the Main
Stage in New York City.
You can attend in person at various cities
across the world or virtually online.
Check out spaceappschallenge.org.
Now to your questions.
The Cosmos asked whether gravitational forces
are about the mass or density of the gravitational source.
Answer-- once you're outside the gravitating
object, what matters is mass.
But how close another object can get before it's ripped apart
by the tidal forces due to a first object, which
is due to gravitational differentials,
that turns out to depend on the density of that second object.
Look up Roche limit on Wikipedia.
R MH, Noah Fence, Fat Lum, Gareth Dean,
and Parrish Danforth all asked in one way or another
why the shell of the moon wouldn't collapse and get
sucked into the black hole.
The short answer is that black holes don't suck.
In fact, far from their horizon, which in this case
would be just centimeters since the horizon is
sub-millimeter sized, the fact that there's
a black hole in play becomes kind of irrelevant.
If you have material that's strong enough
to withstand internal stresses, you
could put a shell that just sits there
around pretty much anything, including a black hole.
Chronoflect asked whether Termina's moon could actually
rip apart in the three day window of the game
if it were the density of Earth's moon.
It turns out that time to disassembly
versus time to impact is a pretty tricky issue.
A lot of factors come into play.
I've seen this modelled in the case
of the Shoemaker-Levy comet that hit Jupiter in 1994,
but I don't recall whether there's a definitive recipe.
I think it depends a lot on the details of the situation.
Raphael Hviding and Daniel Jenkins
asked, wouldn't a black hole as small as the one I'm claiming
evaporate quickly?
In relative terms, yes.
But it would still take ten thousand trillion trillion
times the current age of the universe to do so.
Finally, Patrick Fadgen asked, how can the moon be
seen all day long from Termina?
You'd seem to need the moon to orbit around
the planet at the same rate that the planet spins
on its axis, which I agree is not something
that should happen if the moon is also gradually getting
closer.
It's a major inaccuracy in the game, and as I said,
I don't have all the answers.
Thanks for all the great questions.
Keep it up, and I'll see you guys next time.
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