[MUSIC PLAYING] Oh, yeah, look at right there.

Look, look, look, look, look.

Oh!

That's so sick.

Let's do it again.

Hey, I'm Diana.

You're watching "Physics Girl."

And I should explain what we're doing again.

My friend, Dan Walsh, texted me out of the blue last week and said, ooh, what would happen if you put a GoPro in a closed box with a candle in it and dropped it so it would be in a nearly zero G situation?

And so, obviously, I said, let's try it.

We were not sure if this would work.

Because see, the idea was that in the space station, candle flames do something weird.

Because of the microgravity, candle flames take on a different form and color completely.

And so we were trying to simulate that with our box.

This is how it went.

Are you ready?

26 00:00:55,700 --> 00:00:56,200 Lighting.

OK. 29 00:00:57,198 --> 00:00:58,318 DAN: Oh, my gosh.

Oh, my gosh.

DAN: It's lit?

KYLE: It's lit.

Yeah.

Woo!

Still on fire.

Are you serious?

I can see it, yeah.

DIANA: We took a look at the footage after the first drop.

But it was-- It was so fast.

That was really fast.

But something totally happened.

It was so fast.

But since we filmed at 120 frames per second, we were able to slow down the footage.

47 00:01:20,790 --> 00:01:21,520 DAN: It got so-- 49 00:01:21,602 --> 00:01:22,015 KYLE: Look, look, look, look, look!

DIANA: Oh!

52 00:01:25,480 --> 00:01:26,970 Whoa!

What?

That right there-- that's why we were freaking out over a box.

It's a spherical flame, just like you'd see aboard the space station.

In microgravity or zero gravity, flames burn colder.

And if undisturbed, they'll burn with more of a spherical shape.

But we had a problem.

How can we get higher?

Get on the roof, Kyle.

Well, can you get up there?

How much time are you going to get?

KYLE: I don't want to get up there.

I'll get up there.

[LAUGHS] KYLE: How?

I don't know.

70 00:01:52,860 --> 00:01:53,735 KYLE: Is there like-- Significant.

Somewhere, like a building?

74 00:02:03,620 --> 00:02:04,430 We'll do it.

Boom-- I mean, drop.

Drop.

Drop it like it's hot.

Pew.

Like literally, because it's a flame.

81 00:02:21,099 --> 00:02:21,599 Ready?

Yeah.

Whoa!

Oh, yes!

I think the candle went out.

We did a couple more drops here.

The advantage of the bridge is that it gives more time in free fall, not a whole lot more time, though.

The time scales as the square root of the height.

So we went up from about half a second to about a second and a half.

But even that increase was enough to give us this awesome footage.

96 00:02:52,320 --> 00:02:53,924 Did you see that at the end?

Ah!

The giant flame jet, it's all part of the science behind why flames have the shape that they do and why NASA is still studying how flames burn on the space station.

So flames usually have that teardrop shape because of gravity.

Hot air from the burning wick is less dense than cooler air.

So the hot air rises up and is replaced by cooler air, creating a flow around the flame.

And that elongates it.

And it brings in more oxygen to burn brighter.

Now take away gravity and you no longer have up.

So there can be no buoyant force pushing in any one direction.

So the hot air slowly mixes in all directions.

And chemical diffusion starts to come into play too, to create more mixing.

Because there's all that concentrated fuel at the center of the flame, so you get more mixing.

But it's still slower than if you had a steady flow of air.

NASA ignites fuel fires in space to study how flames spread in microgravity and to study unusual phenomena like cool flames.

So very little airflow, less oxygen, cooler, dimmer flame, and no buoyancy force, and the flame forms a spherical shape.

That's what happened here with our flame, which is super cool.

Because that means that we're demonstrating that falling toward the Earth, pulled down by gravity, is just like floating out in space with no gravity at all.

Boom-- Einsteined.

And the thing is, all experiments are indistinguishable between doing them in free fall with no air resistance and doing them in space, which is why I was able to feel weightless in a zero G plane earlier this year.

The plane was essentially in free fall.

There's another parallel here, too.

During the zero-G flight, we were feeling weightless while diving in the plane.

But then we had to pull out of the dive so as not to hit the ground.

And during that part, you feel really heavy, like almost twice the pull of gravity.

Because in that moment, the plane is accelerating back upwards.

And the same is happening here.

The sheet catching the box is creating a sharp, strong acceleration upwards on the box.

But the air inside should want to keep going down because inertia.

So you'd think that the air and the flame and everything would just collapse at the bottom of the box.

Not so, because while, yes, most of the air does gather at the bottom of the box, it's still much more dense than that hot flame air.

So suddenly, you get a huge buoyant force.

And that pushes up on the hot air, shooting the flame jet upwards toward the top of the box.

Pretty cool.

So one thing I'm still bothered by is that toward the end of the shot, you notice that the flame starts to get less sphere-y and more lame.

We thought maybe there's an air leak or too much air resistance.

So we tried a few fixes.

Now everybody knows I'm an engineer, because all I use is hot glue and duct tape.

DIANA: We even brought an entourage the second time.

But I think that we're still getting a lot of air resistance because of the box shape and some rotation on the box.

So perhaps if you wanted to try this at home, you could 3D print a teardrop shape to drop or something.

I don't know-- to be continued maybe?

But for now, thank you so much for watching.

Happy physics-ing.

And I have to give credit where credit is due.

Dan Walsh, I have to thank you so much for that idea.

Thank you.

And for the same day idea and execution.

And Kyle, I have to thank you so much for being the engineer.

Give me some hot glue, I can make things happen.

[LAUGHTER]