Vsauce!
I’m Jake and while playing the game The
Witcher 3…I cut a lot of people in half…like
a lot of people.
Now the character Geralt has super human strength
which might be why its easy for him to bisect
his enemies.
But we see it so frequently in movies and
video games.
There are even two TV trope pages that list
numerous examples throughout fiction.
Which got me thinking…is it possible, in
real life, with a sword could you cut someone
in half?
The physics of successful flesh cutting is
all about minimizing bulk flesh deformation
while exceeding absolute tensile and sheer
strength.
Now flesh is easy to cut under pressure, but
it also stretches and compacts absorbing the
blades momentum.
So first things first, we need an exceedingly
sharp sword if we want to be able to cut somebody
in twain.
However, not all sword are created equal.
In Mark Miodownik’s book ‘Stuff Matters’,
he talks about the process of forging a samurai
sword.
He mentions that by the 15th Century, the
sword steel made by the samurai were the best
that have ever been created.
They were made from a type of steel called
tamahagane.
Which itself was made from volcanic black
sand.
Besides having an incredibly sharp and strong
sword, you need an incredibly skilled person
to wield it.
Expert swordsmen were used in tameshigiri…the
Japanese art of target test cutting.
Today people use special rolled mats to test
out their blades.
But in the 15th century, swords were rated
by how many people it could cut in half in
a single stroke.
The number of bodies bisected was etched on
a blade as a quality rating.
Two full bisections was considered good.
But there are swords in museums with ratings
of 5.
Mostly cadavers were used for testing but
sometimes the blade would fall on convicted
criminals.
To slice skin you need a blade with an edge
no wider than 100 microns.
About the thickness of a piece of paper.
So far we have the 3 Ss: strength, skill,
and sharpness but there is one more that’ll
help us determine if we can successfully cut
someone in half…stroke!
Physicists at Harvard published a paper entitled
“Slicing Softly with Sheer.”
If you’ve ever had to cut a piece of meat,
you don’t just push all your force on the
knife unless you want to cut very ineffectively.
What you do is press down on one end and bring
the blade across.
You want to carve, not dice.
In the paper they concluded that sheering
minimizes the bulk deformation, squishing
of flesh, before a fractured nucleus, you
break cells apart.
But here’s the thing, we can use science
to try calculate cutting someone in half but
there is also a healthy dose of luck involved.
Excuse me.
Cutting through the flesh is the easy part,
where the trouble comes in is the spine.
You have to strike the person right in the
area below their lower rib and above their
hip.
Not a giant target and you’d have to deliver
over 200j of energy to both the flesh and
the spine.
Assuming a super sharp 10 micron edge.
Eh, I’m gonna *awkward dance*.
Watching Geralt spinning bisection move, his
360 spin happens in less than half a second.
That tells us that he’s delivering around
170j through the blade.
Less than needed but actually just enough
energy if he manages to strike through an
intervertebral disc and miss bone.
Geralt must be incredibly skilled or preternaturally
fast.
If we assume the move is over in an almost
impossible quarter of a second, then he delivers
a healthy 680j and could probably cut 3 people
in half in one move.
So can a human do this?
Well, tameshigiri tells us yes, under special
conditions.
Probably those convicts and cadavers weren’t
moving too fast.
In a real fight?
Well, we just happened to have a master swordsmen
and anatomically correct ballistics dummy
to find out.
So we were able to get all the way through
the torso until hitting the spine directly.
Which we thought would give us trouble anyway.
Also, in the footage you can see how much
momentum of the sword this ballistics gel
was absorbing.
It was insane so lets try something else…
As we found out, it takes more than just being
an incredibly swordsmen or having an amazing
weapon to be able to cut somebody in half.
It also takes a lot of luck.
Maybe next time my friend.
You’re a little shorter than I remember
you.
And, as always, thanks for watching!
