- What happens when you take two and a half meters
of PVC pipe, stuff a ping-pong ball inside,
cover each end with thermal blanket Mylar,
suck out 98% of the air, put a soda can on one end
and puncture the Mylar at the other end?
Okay, every body ready?
Three, two, one.
(bang)
- [Brandon] Wow, that was very loud
- Let's see the damage on the can.
That is some epic damage.
Most of the energy went into the destruction of the can
this time, not in the ping-pong ball.
Hey I'm Diana, you're watching Physics Girl
and I love this demo because it's obnoxiously loud,
destructive and demonstrates some really cool physics
related to space.
So I'm gonna use this demo, not because I want to
shoot ballistic ping pong balls at everything
but because we can use it to dive into some great,
but seemingly unrelated questions.
Question one, how do you use ping pong balls
to make car crashes safer?
Question two, could you survive a hole in the space station?
And question three, what would it feel like to get hit
by a ping pong ball going 400 kilometers an hour.
Yes, someone did this for science and we're gonna show it,
it was not me.
So, I figured making a ping pong cannon would be hard
but this one took us 30 minutes.
We're gonna suck all the air out of this tube.
This is the upgraded version and we'll get to that,
but in the meantime I want to talk about the footage
I can't get out of my mind.
The ping-pong ball smashing into an iPhone, just kidding.
It was a collaboration we did with Brandon
over on his channel.
Link is in the description, check it out.
But no, I can't get out of my mind
the footage of the ping pong ball
smashing into a tennis ball.
You can't even see what happens, the footage is too fast.
So I traveled all the way up to Portland
to film with my friend Darren
with his phantom high-speed camera,
but not just his normal thousand frames per second,
oh no, for the ping pong collision
we had to go up to 18,000 frames per second
on a second camera.
Two, one.
- [Brandon] Look at that.
- Check it out, shooting a can filled with liquid nitrogen,
the ball is in frame for just a fraction of a second
before it hits and this is at 18,000 frames per second.
So we can use some creativity
to figure out how fast the ball is going by knowing,
I mean googling that a standard soda can
is six point six centimeters in diameter, that's our ruler.
Then the ball goes about 0.7 centimeters in one frame
which at 18,000 FPS works out to
0.0000555555 seconds per frame
which all converts to a speed of
12,600 centimeters per second
or about 450 kilometers per hour.
That's fast,
which is fast enough to make an aluminum soda can
keel over in pain.
Aah, but soda cans are not all that strong.
In fact, it's a trick you can do
to rip one in half with your bare hands.
Tear one in half of their bare hands.
In fact, some people can even tear,
tear one in half with your bare hands.
Oh, bruh, but what about when you shoot a tennis ball?
I thought maybe the ping pong ball would bounce back,
maybe the tennis ball would crack, something,
but check it out.
The tennis ball is a beast.
All you see is a small ripple through it and again,
this is 750 times slower than real time.
This brings to mind small puppies
leaping at and bouncing off of big couches.
♪ They ask you how are you able to say that you're fine ♪
♪ And you're not really fine ♪
Or less amusing,
car crashes between massive trucks and small cars,
which brings us to our first question,
how do you make car crashes safer
and what can ping pong ball collisions teach us?
See the correlation?
Ping-pong balls are piddly.
They're no match for the notoriously massive tennis ball.
Ping-pong balls are just about the same mass
as an unwrapped stick of gum, thanks Cody.
I think we all have a sense
that driving a bigger car is safer
but is it as simple as bigger is safer?
My mom seems to think so.
This is her approximate height as compared to Shaq,
so she's tiny
and this is the size of the car that she drives,
for safety she says, but if she were driving a Fiat,
there's my Fiat, this chocolate chip represents her energy
if she's driving at 80 km/h.
If a Semi were going at 80 km/h, this would be its energy.
So yeah, the truck has a lot more energy.
I'm gonna take my mama out of the car for this
next hypothetical situation.
Okay, imagine a driverless Fiat and a driverless Semi
are going towards each other at 80 km/h each
and they crash, head-on, the crash wouldn't look like this,
it would look more like this.
The Fiat would be pushed backwards
up to a velocity of 76 km/h
because though all of this kinetic energy
isn't all conserved, some of it gets gobbled up by heat
and friction and deformation of materials and so forth,
but momentum is conserved
and there's a whole lot more of it going in this direction
at the beginning of the crash.
Yo, that's insane, 'cause you know what that means?
The Semi was initially going forward at 80 km/h
and it can end up going backwards at 76 kilometers per hour
which in total is a speed change of 156 kilometers an hour
which is like hitting the wall going 156 km/h,
which is why the casualty rate per million,
one two three year-old minis, another small car in 2007
was three times that of large cars.
People looked into banning large cars from city centers
because of this physics
and also because traffic congestion sucks.
So we've learned that math is important in crash safety.
Here's the ping-pong ball against the basketball
which weighs in at a whopping 500 grams.
I love that shot because I used kind of a flat basketball
and it ripples like, boom.
So what if we shot a ping-pong ball
against a ping-pong ball?
Same masses.
- Whoa.
- I should mention that this footage is on my camera
at 940 frames per second
which is nothing like Darren's beast.
You can't even see the ping-pong balls as they go,
they're like a smear as they go by
but here's the aftermath of them.
So you're not guaranteed to be okay
even if it's just two small cars colliding,
because obviously speed is a factor.
In fact it's so important that if
this is the energy of a Fiat going 10 kilometers an hour,
50 kilometers an hour, oh-oh,
gonna need some more chocolate chips.
100 kilometers an hour, 150 kilometers an hour
because energy goes like velocity squared
which is why you don't want to get in an accident
going way above the speed limit
or while I'm driving at all.
Stay home but also, materials are important.
Ping-pong balls are made out of a material that tends to
shatter like glass.
It's called celluloid and interestingly
it's the same stuff billiard balls and film strips
are made of.
If a car was made of celluloid or acrylic
like this actual car, it would probably shatter on impact
but this Bugatti made of Legos would maybe fare better
because one, Legos are made out of ABS plastic
which is tougher,
as anyone who's ever stepped on those little devils knows
but also two,
because the Lego car would probably break apart
that as they break apart they redirect energy
into motion of the pieces
rather than into damaging the contents,
but for the Lego car that means unfortunately,
debris flying at your face so you know, lose-lose,
but this fracturing process
actually gives the ping-pong ball less penetrating power.
If it were a tough steel ball that weighed the same amount,
sheesh, watch out bro.
So would you be better off in a car made of rubber,
like a tennis ball car?
No stupid questions.
Well, here's the problem with that.
In a car where you just bounced off
the collision would actually be more dangerous.
If our tennis ball Fiat crashed with our tennis ball Semi,
you could get a situation where the Fiat
is torpedoed backwards
but the more dangerous part for you for your body
is the number of G's that you would feel.
Get this, when they do high G-force testing,
that testing equipment goes up to about 20 G's.
Regular humans tend to pass out before 10 G's
and the human body has been shown to withstand over 46 G's.
We know this thanks to crazy humans.
In the 1950s pilot John Stapp was strapped to a rocket sled
rocketed to a max velocity of 1,017 kilometers an hour
and was slowed down to zero in 1.4 seconds,
experiencing 43 G's.
He survived and in other experiments
survived up to forty six point two G's.
This was him experiencing that acceleration
in the forward backward position though.
The problem if he experienced that acceleration
in the line from your head to toe
is that it would push the blood up to your head
or down to your toes
and you wouldn't be able to maintain that blood pressure.
The other thing when you experience accelerations this high
is that your organs want to stay behind
when your body accelerates forward, which is not good.
So how's all this related to our tennis ball car?
Well, best case scenario
your tennis ball car hits the Semi and it balances backwards
going the same speed it was going forwards,
so you're just gonna be going
at all the other cars on the highway
at 80 kilometers an hour, not ideal.
Also, during the moment of that collision,
chances are you're going to have experienced
a very high G-force
because your change in velocity was so big
and typically the collision time is really small
even with rubber that's what creates the G's,
a big velocity change over a short amount of time.
You would have this same problem
if the car was made out of steel
because it would maybe bounce back
and the car would be intact
but in an even shorter period of time,
see you would experience even higher G's
than if it were made out of rubber.
So what's the happy medium
between your cars splitting apart like a ping pong ball
and it bouncing back like a tennis ball?
Well, crumple zones.
This is what cars have now-adays.
Cars nowadays have noses made out of materials
that are meant to be destroyed and as they crumple
they lengthen that time you're slowing down
so you don't feel that hard spike of G-forces.
You experienced a longer lesser force,
still not comfortable but enough to maybe save your life.
Couple that with seat belts and airbags and all the bells
and whistles of car crashes
plus a passenger safety cell that is made out of steel
or something really strong and rigid
to protect the precious cargo
so you don't get too close to the crumple zone parts.
So, the safer cars have strong parts
but also weaker parts on purpose.
So what have we learned from the ping pong ball cannon
on how to crash safer?
Crash cars the same size going slowly
with the right crumbly material, a crumple zone,
a strong compartment around the precious cargo
and do a crap-ton of testing
because you never know how it's gonna hit
and if it's gonna spin and that's gonna change everything.
So basically, everything crash testers have done
for the last century
which is why in this crash between a 1959 Bel Air
and a 2009 Chevy Malibu, I'd rather be in the latter.
Okay, we made it question two,
can you survive a hole in the space station?
We're gonna look into this question by asking,
how is it possible to get a ping-pong ball going 450 km/h?
Which you might not think is that hard
because you saw that janky device that we made but get this,
let's say you, an average human,
can throw a ping-pong ball at 80 kilometers an hour,
the ping pong ball would immediately start slowing down
at seven G's.
That's a lot.
From Air drag alone
and that drag just goes up the faster you throw it,
so obvious solution, you remove the air, suck it out,
create a vacuum just like the vacuum of space,
except not quite that intense.
A true vacuum is actually even more intense in space
because space has a particle here and there
but like, very sparse.
Less than one atom per cubic meter.
That's like half an atom inside of the space in your Fiat.
For reference, the strongest vacuum system here on earth
is that CERN's Large Hadron Collider
pulling a vacuum down to
almost as strong as the vacuum on the surface of the moon
but still about ten trillion atoms per Fiat.
We don't want to get that far, no,
we want to just get to about 95 percent of a total vacuum.
That's gonna be enough for us to reduce the drag.
Then we utilize one of the strongest forces we know,
we let the air rush in.
Don't believe me that that's one of the strongest forces
we could possibly use?
Well, if we were able to get a full vacuum in that tube,
then the acceleration you'd get on the ping-pong ball
would be 4,700 G's.
Oh yeah, do you believe that?
It's true.
That's how you get a ping-pong ball
up to 450 kilometers an hour.
That and you make the ping-pong cannon longer
so that it has more time to speed up with no air resistance,
which is what we do with our new and improved cannon.
So actually, that one's shooting
at higher than 450 kilometers an hour.
- [Brandon] Two, one.
Wow, that's crazy
- I know right. - Ping-pong ball did that.
But there is a limit to how fast you could get
because there ends up being some effects along the walls
of the pipe between the ping-pong ball gets complicated.
Okay so this situation
of vacuum on one side of the ping-pong ball,
air rushing and pushing on the other side
seems a lot like a situation you'd get
if you were in the International Space Station
where you've got air on the inside vacuum on the outside
and you've got a breach in the hole.
So, if you had a hole in the space station,
let's let our imaginations run wild
and then reel them back in
with the cold hard reality of physics and outer space
because it's cold and hard.
So in my imagination I imagine you getting like pushed out
really fast through the hole
and all this debris flying at you like the ping-pong cannon.
So if there were a whole breach
roughly the size of your pinkie,
it would take about six minutes for the entire
space station to decompress, which is a while
but still kind of terrifying but you'd survive.
We know because have been holes in the space station, yeah,
and astronauts just find them and fix them.
I had no idea,
I thought it would be explosive decompression.
So for that to happen on the ISS
you would need a very large hole,
probably about the size of a human
and even with a hole that big
you'd have to be right next to it
in order to get sucked out.
Even just being a meter or two back,
the air would rush around your body
faster than it would push you forward.
So you'd probably stay inside the cabin,
although you wouldn't be much better off
in a cabin with no air.
So not only could you survive a hole in the space station,
at least a tiny one,
it turns out that that would be less dangerous
than getting hit in the head with a ping pong ball cannon
or the ping pong ball from the cannon.
Anyways, this leads us to question number three which is,
what would it feel like to get hit with a ping pong ball
from the ping pong ball cannon?
Here's a video from a professor that allowed his students
to shoot him with a ping pong cannon in the stomach.
- Do it on three.
- [Student] Three, two, one.
(students gasping)
- That is madness.
I want to reiterate though this was in the stomach
and not in a head.
A head shot could potentially be fatal and by the way,
we stood back, we wore safety goggles.
It was all adults doing this, no children.
All right, check out Brandon's video from gizmos slip
to see what happened to the iPhone's screen
when we shot a ping pong ball at it in the original Canon.
Link is in the description.
- The biggest surprise for me
was the speed at which the ping pong ball can exit the tube.
I understand how like when you smack a ping pong ball
it can only go so fast because the air slows it down
really quickly. - Yeah, exactly.
- But the sense of tube is vacuum if you just get
so much more speed.
- All right fist bump.
- Yes.
- I hope you enjoyed learning about the strange science
of the ping pong ball cannon.
Thanks for watching and happy physics-ing.
(upbeat music)