HOST: What happens when you take 2 and 1/2 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?
[buzzing] OK, everybody ready?
Three, two, one.
[loud pop] MAN: 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 Dianna.
You're watching Physics Girl.
And I love this demo because it's obnoxiously loud... [loud pop] destructive, and demonstrates some really cool physics related to space.
So I'm going to 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 going to 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 going to 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.
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 1,000 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... [BLAST] MAN 1: Look at that.
DIANNA: 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 6.6 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 0.00005555 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.
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 with their bare hands.
In fact, some people can even tear one in half with their bare hands.
Oh-- [GROANS] 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.
WOMAN 1: They ask you how you are.
You just have to say that you're fine.
And you're not really fine.
DIANNA: 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.
I think we all have a sense of 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-- here's my Fiat-- this chocolate chip represents her energy if she's driving at 80 kilometers per hour.
If a semi were going at 80 kilometers per hour, this would be its energy.
So, yeah, the truck has a lot more energy.
I'm going to take my mama out of the car for this.
Next hypothetical situation.
OK, imagine a driverless Fiat and a driverless semi are going towards each other at 80 kilometers per hour 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 kilometers per hour.
Because though all of this kinetic energy isn't all conserved, some of it gets gobbled up by heat and friction and defamation 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.
Because you know what that means?
The semi was initially going forward at 80 kilometers per hour.
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 a wall going 156 kilometers per hour, which is why the casualty rate per million one-to-three-year-old Minis, another small car, in 2007 was three times that of large cars.
People have looked into banning large cars from city centers because of this physics and also because traffic congestion sucks.
So we've learned that mass is important in crash safety.
Here's the ping-pong ball against a basketball, which weighs in at a whopping 500 grams.
I love that shot because I used a flat basketball.
And it ripples like "bla-uu."
So what if we shot a ping-pong ball against a ping-pong ball?
DIANNA: 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 OK even if it's just too 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-- uh-oh, going to 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 driving at all.
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, cause the LEGO car would probably break apart, that as they break apart, they redirect the 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, 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 Gs that you would feel.
When they do high G-force testing, that testing equipment goes up to about 20 Gs.
Regular humans tend to pass out before 10 Gs.
And the human body has been shown to withstand over 46 Gs.
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 Gs.
He survived, and in other experiments, survived up to 46.2 Gs.
This was him experiencing that acceleration in the forward-backward position, though.
The problem if you experience 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 as high is that your organs want to stay behind when your body accelerates forward, which is not good.
So how is all this related to our tennis-ball car?
Well, best case scenario, your tennis-ball car hits the semi.
And it bounces backwards going the same speed it was going forwards.
So you're just going to 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 Gs-- a big velocity change over a short amount of time.
You would have the 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.
So you would experience even higher Gs than if it were made out of rubber.
So what's the happy medium between your car splitting apart like a ping-pong ball and it bouncing back like a tennis ball?
Well, crumple zones.
This is what cars have nowadays.
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 experience 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 going to hit.
And if it's going to spin, then that's going to change everything.
So basically everything crash testers have done for the last century, which is why this crash between a 1959 Belair and a 2009 Chevy Malibu, I'd rather be in the latter.
OK, we made it to question two.
Can you survive a hole in the space station?
We're going to look into this question by asking, how is it possible to get a ping-pong ball going 450 kilometers per hour, 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 Gs-- 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 up, 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.
It's like half an atom inside of the space in your Fiat.
For reference, the strongest vacuum system here on Earth is at CERN's Large Hadron Collider, pulling a vacuum down to almost as strong as a vacuum on the surface of the moon, but still, about 10 trillion atoms per Fiat.
We don't want to get that far, no.
We want to just get to about 95% of a total vacuum that's going to 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 Gs.
Woo, yeah, do you believe that?
That's how you get a ping-pong ball up to 450 kilometers an hour.
That, and you make the ping-pong canon longer so that it has more time to speed up with no air resistance, which is what we did with our new and improved cannon.
So actually that one's shooting at higher than 450 kilometers an hour.
MAN 2: Two, one.
[pinging] Wow, that's crazy.
DIANNA: I know, right?
MAN 2: The ping-pong ball did that.
DIANNA: But there is a limit to how fast you can get because there ends up being some effects along the walls of the pipe between the ping-pong ball.
It gets complicated.
OK, 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 hull.
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 pushed out really fast through the hole and then all this debris flying at you like the ping-pong cannon.
So if there were a hull breach roughly the size of your pinky, 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 there 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.
Anyway, 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.
SPEAKER: Three, two, one.
[BANG] [APPLAUSE] That is madness.
I want to reiterate, though, this was in the stomach, not in the 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.
The biggest surprise for me was the speed at which the ping-pong ball could exit the tube.
I understand how when you smack a ping-pong ball, it can only go so fast because the air slows it down really quickly.
DIANNA: Yeah, exactly.
But since the tube is vacuumed, you just get so much more speed.
All right, fist bump.
I hope you enjoyed learning about the strange science of the ping-pong-ball cannon.
Thanks for watching and happy physics-ing.