MICHELE NORRIS, Host:
We recently noticed a genre of videos making their way around the web. They're generally made in a back yard involving young men and a two-liter bottle of Diet Coke, and also a handful of the mint candy called Mentos.
What happens next is the Mentos are shoved into the bottle and the Diet Coke erupts, spewing about 12 feet into the air. We found close to 100 different videos, some highly produced, some even have a soundtrack.
SOUNDTRACK PLAYED FROM DIET COKE WEB VIDEO
NORRIS: And others with a more minimalist charm.
(SOUNDBITE FROM VIDEO)
TORI SIMPSON: Hi. I'm Tori Simpson and this is my science fair project. It's about what happens when you put Mentos into soda. I'm doing it with warm soda and cold soda to see which one goes higher. My hypothesis is that cold soda will go higher.
NORRIS: Actually, Tori found that warm soda made for a higher geyser. Well, we had to see this phenomenon up close and personal. We wanted to see it for ourselves. So we gathered up all the necessary ingredients. Our science correspondent, David Kestenbaum, producer Brendan Banaszak and a large number of NPR employees, I guess looking for an excuse to get out of the building on a nice day.
NORRIS: Well, it's a beautiful day. We're outside the offices of NPR's national headquarters on Massachusetts Avenue in Washington, DC. I'm here with NPR's science correspondent David Kestenbaum who is going to walk us through this experiment, explain to us what's going on and tell us a little bit about the science behind this.
Brendan Banaszak is leaning over a two-liter bottle of Diet Coke. He's opening that, he's got a box of Mentos at the ready. They're opened and he's emptying the Mentos and he's dropping them in. This has to be done very carefully and very fast. You have to get exactly the right number of Mentos in there.
DAVID KESTENBAUM: Brendan is expendable.
NORRIS: And Brendan is going to be brave. He just gave us a thumbs-up.
KESTENBAUM: He's given us a thumbs-up.
NORRIS: We have to watch it percolate now. There it goes.
NORRIS: Holy Toledo!
KESTENBAUM: How high do you think that was?
NORRIS: I think that was 12 feet. What do you think?
KESTENBAUM: Yeah, and the bubbles are going down. There doesn't appear to be much liquid left in the bottle.
NORRIS: Mm, looks like we've got almost everything. There's about an inch left.
KESTENBAUM: Brendan, are you okay?
BANASZAK: We're okay.
NORRIS: He'll be sending us his dry cleaning bill. Can you explain the science behind all this?
KESTENBAUM: Well, I did talk to a senior scientist at the American Chemical Society and he said the traditional way to do this, when he was a kid, was they would drop M&Ms in a bottle. But he said it would mostly just fizz up.
And I said, no, no, no, we're talking about a geyser, you know, 10 feet high, and he says, you're kidding me. Then I showed him the video.
NORRIS: That was 10 feet.
KESTENBAUM: And he was very impressed. So the consensus seems to be that what's going on is that the Mentos provide a surface for all of the little carbon dioxide molecules to get together. When you open a bottle, normally the carbon dioxide dissolves in the soda, right? And it comes out slowly.
NORRIS: That's what you hear when you first open the bottle.
KESTENBAUM: Yeah. And the reason it comes out slowly is because you've got a kind of lonely molecule of carbon dioxide there. It's got liquid around it that's sort of holding it there and it needs to meet up with other carbon dioxides and make a bubble, and then it can get out.
And so when you drop the Mentos in, the Mentos apparently have a very rough surface, so they actually have a lot of surface area. So all the little crevices and stuff, there are places where the carbon dioxide can nucleate. This is sort of like when, you know, when it rains for a cloud to form the moisture in the air needs a little particle of dust to gather around.
So it's a similar idea here. And, anyway, all the carbon dioxide then gets together very quickly at the bottom and you get a rush of all the gas being released all at once, and it throws out a lot of the soda bed above it.
NORRIS: Well, David, thank you so much for getting us out of the studio.
KESTENBAUM: Yeah, you're welcome.
NORRIS: It was good fun.
BANASZAK: Thank you.
NORRIS: We're not sure if we should be telling you to do this at home, but if you want to see a video of David Kestenbaum risking it all in the name of science, go to our website, NPR.org.
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