- Today's episode of Because Science
is sponsored by Birth of the the Dragon.
Birth of the Dragon hits theaters everywhere August 25th.
(karate yell)
What is the most-famous martial arts move?
In terms of sheer popularity, I'd argue
that it is the one-inch punch.
And I think it's so popular because it looks impossible.
Like it's generating too much force
for how much space it has to do so.
But it's not impossible.
It's not magic.
It's not chi.
It's physics.
(karate yell)
The story goes that the West was introduced
to the one-inch punch through a demonstration
by the dragon himself at the Long Beach International
Karate Championships in 1964 and as you can see,
dramatized in the upcoming movie Birth of the Dragon,
it hits confusingly hard.
Here's one slowed down.
It's a legitimately wow move, so how does it work?
The martial artist was obviously in fantastic shape.
But with only one inch to work with,
it looks like all that power we see
in the demonstrations has to come from somewhere other
than just arm muscles, and it does.
Martial artists call this kinetic linking,
but a physicist looking at the one-inch punch
would call it kinematic chains.
Wait, wait.
That is three inches.
Should we tell someone?
A kinematic chain is an assembly of rigid bodies
connected by joints in some way.
Now think of the entire human body
as an assembly of kinematic chains.
What the dragon did and what all good martial artists
do is punch with more than just their fist.
It starts at the ground, translating motion
in feet and thighs into the torso, into the arms
and then all the way to the end point, the final punch.
In this way, they punch with more kinetic energy
than the fist would have otherwise.
How much kinetic energy a fist has upon impact
will determine the impact force.
Energy and force are often used interchangeably
when talking about fight physics,
but they are not the same thing.
Let's start with work.
Work is some force applied over some distance.
Now let's add in Newton's Second Law,
that says force is equals to mass times acceleration.
Now let's add in one of the kinematic equations
of motion, remember those chains?
And finally, we expand the expression.
Since work is also a change in kinetic energy,
you have to apply a force over some distance
to make something move,
we end up with the equation for kinetic energy.
If the object starts at rest.
So the faster I move my mass,
the more kinetic energy it gets.
Now that we know how the equation
for kinetic energy works, we can explain
where all the power behind a one-inch punch comes from.
Looking back at the equation for kinetic energy,
we can see that an object's velocity
can be much more important than its mass,
because it's a squared value.
Secondly, we can see that force and energy
are related, but not interchangeable.
It depends on how you apply that
Wait.
It depends on how you apply that energy.
I said wait.
Rearranging values again in this equation,
we can see that the more distance
the change in energy occurs over,
the less force is imparted.
This is exactly why cars have crumple zones.
The further the crumple goes,
the less force is applied to you,
and that's good.
That's why, to perform a successful one-inch punch,
you want to do the exact opposite,
and bring all the kinetic energy
that's in a fist to a stop in a short distance.
Look at how short of a distance
this fist covers before the punch is over.
That increases the force.
Another way to interpret this relationship
is a change in momentum,
which is mass times velocity over time.
If you bring all of the momentum of a fist
to a stop in as short amount of time as possible,
the force goes up.
I think this makes more intuitive sense.
The faster you hit, the harder you hit,
and Lee emphasized incredible speed in his fighting style.
He was so fast, that some trained martial artists
couldn't even block his punches.
What happened?
This is how a one-inch punch can impart so much force
by expertly minimizing either distance covered,
or time elapsed.
But that's not everything behind the punch.
(karate yell)
Lee wasn't a big dude.
He was my size, but apparently, he hit like a big dude.
That's because in both momentum
and kinetic energy equations, velocity is critical.
And since I can't change the mass of my fist,
if I hit as quickly as possible,
I can hit like a guy twice my size.
Form is a factor, too.
If you didn't have the concentration,
training, and focus to perfectly align
your kinematic chains, force is gonna be lost.
With perfect form, you are minimizing the distance
and time it takes to finish a punch,
thereby increasing the force,
but if your form is even just a little bit off,
you will increase the time and the distance
it takes to finish the punch,
and become like a car's crumple zone, lowering the force.
The final component of a one-inch punch is psychology.
Look, when you're being punched by the most famous
martial artist in the world,
or who would become the most famous,
you're gonna sell it a bit.
There's no way this guy is actually
getting punched across the room.
Reputation has something to do with it,
and that's kinda cool.
So why is the one-inch punch so powerful?
Well, it minimizes impact distance and impact time,
it takes advantage of body positioning and kinematic chains,
and it has a reputation behind it.
It's never gonna be as forceful
as a giant haymaker thrown by a giant fighter
because physics, but when performed by a master,
it's an incredibly efficient way
to produce a surprising amount of force
across almost no distance in almost no time,
because science.
(groans)
oh, that was, oh dude, that was more than one inch.
Thank you so much for watching, Joe.
If you want even more silliness,
check out my new show with Dan Casey, my colleague,
where we get very silly about a very serious man,
called Muskwatch and if you want even more science,
but a little bit more premium, check out my show
the S.P.A.A.C.E. Program on ProjectAlpha.com
if you subscribe to that, you can get that show
and this show two days earlier than you otherwise would.
Thanks for watching, I already said that.
Thank you, though.
And thanks again to Birth of the Dragon
for sponsoring today's episode.
The movie is inspired by true events.
To see the one-inch punch on the big screen,
check out Birth of the Dragon in theaters August 25th,
no cameras, no rules, no limits.
Come on, oh, oh, might fly out of your hands
and hit you right in the eye.
Okay, hold it, come closer.
Alright, alright, one-inch punch,
using everything that we-
- [Woman] Are we rolling?
- Yes.
Everything that we just learned
kinet, kinet, kinetic, kinetic.
Come on, come on, ooh.
Come on, one more time.
Forget it.
(laughter)
He's too good, can't do it.
Okay, now hold it.
- [Woman] No, this is gonna hurt your hand.
- It's not gonna hurt.
Why would it hurt?
It's styrofoam.
Alright, everything we just learned, okay.
Okay, see? We got the distance?
Hold it!
Hold it with both hands, hold it.
Put your hands up.
Okay, okay, okay.
- [Woman] I'm scared your knuckles
are gonna hit my knuckles.
(karate yell)
Yeah.
So you extend your fingers,
that's the distance, you have this distance.
- For force?
- Yeah, so you.
- Just like, like that?
- Yeah.
Stay away from my styrofoam.
You hurt my knuckle.
- [Woman] I'm sorry.
- Get outta here.