- If you've played video games at all,
then you probably know the tropes.
Get enough coins and you get an extra life.
Bad guys always leave red barrels around
filled with exploding juice.
And sometimes your character can jump
and then jump again.
But is double jumping physically possible?
Let's find out.
A number of classic games feature double jumping,
but here is Super Smash Brothers to demonstrate.
Double jumping is when a character jumps
and at the apex of their jump, jumps again.
They move and yet they are pushing on nothing but air.
Many of you have asked me this question over the years,
so let's jump right into it (laughs).
Obviously, in the course of everyday life,
you can't double jump.
You can prove this to yourself if you just (screams).
Of course it would hurt.
How does he--
Like I said, you can try to,
you can try to,
you can try to double jump,
but that effort is wasted.
That's because of what a jump is.
When you jump, your legs apply a force to the ground.
And because Newton's laws state
that there's an equal and opposite reaction
for every action,
when your legs provide a force on the ground,
the ground provides a force on you.
This force accelerates your mass, and you jump upwards.
So what is a double jump then in these terms?
Well, you jump into the air,
and then, once in the air, you press down
or attempt to on the air.
But the air has so little mass, it can only provide
a very small reactionary force,
a force so small that it doesn't accelerate your mass enough
to give you an extra boost up.
Again, you can--
Again, you can prove this to yourself.
Oh, extra life.
Another way to prove
that the classic form of the double jump
isn't really possible is to remove gravity altogether.
Destin over at SmarterEveryDay
actually got to ask astronauts whether or not
a cat's aerial righting reflex worked in outer space.
And you can see astronaut Tom Marshburn here
trying to move his body.
He can rotate it,
but he can't give it any velocity in any direction.
That wouldn't be the case if you could push off the air
like a double jump.
In fact, if you could push off the air like a double jump,
then humans could fly.
And obviously, that's not the case.
While it's theoretically possible
to kick air away from you so fast
that you get an extra upward boost,
I also think that's the least plausible way
of doing a double jump.
How else could we do it?
How dense are you?
Are you full of pasta and fazool?
The conservation of momentum is a fundamental law in physics
that states that momentum,
which is a product of mass and velocity of a system,
does not change overall unless acted on by an outside force.
For example, if I were to--
If I were to jump into this block,
the momentum that I have before I hit it
has to equal my momentum after I hit it
plus the momentum that I give the block.
Because our masses don't change,
I get slowed down, it gets sped up,
and then momentum's conserved.
How do you do that?
I think that we can use the conservation of momentum
to enable a different kind of double jump.
Here's a riddle my fantastic eighth grade science teacher
Mr. D gave me once.
If you have a great science teacher, you should tell them.
Imagine that you are sat in the middle of a frozen pond,
right on the ice.
The ice is totally frictionless.
How do you get back to shore?
I'll give you a second.
Oh, Charles is gonna love it.
The solution is to use the conservation of momentum.
You're stuck in the middle of the pond,
and you can't change your velocity
because of the lack of friction, so change your mass.
If you took off maybe your boot
and threw it in one direction,
you would lose mass.
And because you lose mass but momentum has to be conserved,
you are going to get momentum.
But your initial momentum was zero,
so now you get momentum that's negative,
which is pointing in the opposite direction.
Because the ice is frictionless,
even that little bit of velocity
throwing your boot away from you gave you,
you get back to shore.
What if we solved the double jump problem
like we solved the pond problem,
by throwing your clothes away?
Oh okay, that's where we're going.
It looks like most double jumps start at
the apex of the first jump,
where the initial upwards velocity is finally
completely canceled out by gravity.
Because a greater change in momentum
would come from changing your mass as much as you can,
at this point, you'd want to throw all of your clothes,
all of them.
Oh, oh, why did I do it like this?
Then, if you set up the equation,
you can find out how fast you'd have to throw
all of your clothes away from your naked body
to get an additional upward boost.
Time to add some numbers.
I found a study that says the average person wears around
a kilogram of clothes,
and if the average person weighs around 62 kilograms
and we want a boost at the apex of our jump
to be like a normal jump,
maybe an upwards velocity of three meters per second,
then if you jumped,
waited 'til the apex, got naked mid-air,
and then threw all of your clothes down directly below you
at 150 meters per second, around 350 miles per hour,
you would get a second boost.
You would double jump.
Oh, it touched me.
So, could you ever double jump?
Well, not quite like a classic video game character.
If you had to push down on the air with your legs,
you'd have to do it so hard and so fast,
you'd probably rip your legs off.
A much more plausible, though still pretty hard option,
would be to jump and at the apex, get naked
and throw your clothes down below you
faster than anyone's thrown anything.
Impractical, sure, but still possible.
Hey, get creative with it.
Bring a rocket launcher
and then fire your clothes down for you.
Technically, it would work,
and it would be another video game trope
that we just confirmed.
That was a bad one.
I'm still in frame, bye.
Thank you so much for watching, George.
Make sure to follow me on Twitter @Sci_Phile
where you can suggest ideas
for future episodes like this one
and on Instagram under the same handle
where I'm now posting mini-episodes.
And if you want more silliness, check out Muskwatch.
And if you want higher quality science stuff,
check out the S.P.A.A.C.E. Program also with me.
Yes, I know it's physically impossible
to both kick air so fast that you double jump
and throw clothes at 350 miles an hour,
but it is more practical to throw objects
and use the conservation of momentum than it is to kick air.
Hey, did you know that Yoshi has a full name
like a dinosaur?
It's Yoshi T. Munchakoopas.
Oh, Yoshisaur T. Munchakoopas.