Peep Show: Watch Us Calculate The Speed Of Light With Stale Easter Treats : The Salt NPR's Adam Cole demonstrates a science experiment that offers a new use for old Peeps. All you need is a ruler and a microwave.

Peep Show: Watch Us Calculate The Speed Of Light With Stale Easter Treats

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If you just celebrated Easter, you might have some stale marshmallow Peeps lying around the house. And if you want to avoid eating those Peeps, NPR reporter Adam Cole says that they are the perfect material for a science experiment you can do in your own kitchen.

He shows you how on NPR's science YouTube channel, Skunk Bear, but he promised that we could even do it here in the studio. We just need a microwave. So we have set one up right here next to me. And, Adam, is that a tray full of incredibly unappetizing Peeps that you have there?

ADAM COLE, BYLINE: Yes. This is a giant casserole dish chock full of purple, orange and blue Peeps. And believe it or not, we're going to use this humble Easter treat to calculate one of the constants of the universe - the speed of light.


COLE: That's right. It's so awesome I wrote a song about it.

UNIDENTIFIED SINGERS: (Singing) Finding the speed of light with Peeps.

COLE: Here's the trick. Microwave ovens use microwaves to heat your food. And those waves just so happen to travel at the speed of light. So what we're going to do here right now is find out how fast those microwaves are going.

SIEGEL: And then we'll be able to calculate the speed of light.

COLE: That's right.

SIEGEL: Rather than just look it up on the web.

COLE: That's right. We're going to do it the hard way.

SIEGEL: So where do the Peeps come in?

COLE: Well, hold on. We'll get into that in a second. But first, we're going to need a little bit of physics. There's this handy equation for finding the speed of a wave or a microwave, even. The speed is the wave's wavelength times its frequency.

SIEGEL: And you have to remind us what the wavelength is.

COLE: So that's just the distance between the top of one wave and the top of another wave.

SIEGEL: And the frequency is how many waves it makes per second?

COLE: That's right. And it turns out we can physically measure the wavelength of the microwaves in this oven. Now, Robert, if you've ever microwaved a burrito - and I'm not saying you'd ever stoop this culinary level but if you did - you might have noticed that when you get it out of the oven, there are areas where the beans and cheese are boiling hot.

And then there are areas that are still frozen solid. And that's because the microwave oven has these hot and cold patches. And it turns out, those hot patches are evenly spaced. They're half a wavelength apart.

SIEGEL: And so you can then start to solve your equation.

COLE: And this is where the Peeps come in.

SIEGEL: I should say that I've only microwaved burritos in the interests of science, not supper.

COLE: That's the best way to do them.

SIEGEL: You've got this rectangular glass dish here with the Peeps packed together like pieces of a jigsaw puzzle. As I say, incredibly unappetizing.

COLE: (Laughter) That's right. They're not looking too tasty. So I'm going to open the microwave and take out this rotating tray.

SIEGEL: Normally that would move the dish around.

COLE: Yeah. The Peeps would rotate in and out of hotspots and be heated evenly. But I want those Peeps to stay put because I want to see where the hot spots are. So I'll just put the dish in here.

And we're going to set the power on low. And it really does have to be a low setting. We don't want those Peeps to just explode if it's on full power. And let it run for a minute or so.

UNIDENTIFIED SINGERS: (Singing) Finding the speed of light with Peeps.

COLE: Through the magic of radio, a full minute has passed. And now I'm going to poke around a little bit and just see where things are warm and melty.

SIEGEL: So we find melty spots and also some hard spots that aren't melty among the microwaved Peeps.

COLE: Yeah. You can sort of feel around. And, look, there's another part that's melted a bit.

SIEGEL: OK. We have the two skewers. And you're standing them up. And I'll put a ruler to measure the distance between them. And I'd say that they're about, well, 2.5 inches let's say between those two skewers. What does that tell us?

COLE: Well, remember, the distance between the hot spots is half a wavelength. And so we've got our half a wavelength, 2.5 inches, double it. You've got the wavelength, 5 inches. And now remember our equation?

SIEGEL: (Laughter) No - wavelength.

COLE: The speed is the wavelength of the microwave times the frequency of the microwave.

SIEGEL: But how do we know the frequency, Adam?

COLE: Well, conveniently it's written right inside the microwave door.

SIEGEL: That's my kind of experiment.

COLE: It basically says 2,450 - what does that say? - megahertz.

SIEGEL: So 2,450 megahertz.

COLE: That's right. That means that these microwaves are vibrating up and down 2.45 billion times every second. So we multiply that frequency times our wavelength and we get - let me just do this math here. So we get 12.25 billion inches per second. Let's translate that to a little more friendly of a number.


COLE: That comes out to 193 miles per second.

SIEGEL: I learned the speed of light was 186,000 miles per second, so...

COLE: So there you go. We're pretty close.

SIEGEL: And we're pretty fast, too.

COLE: That's right.

SIEGEL: But anyway, close enough for public radio work.

UNIDENTIFIED SINGERS: (Singing) We just found the speed of light with Peeps.

SIEGEL: Well, we've just heard one of the most fascinating things you can do with marshmallow Peeps - determine the speed of light. You can watch Adam explain the history of the search for the speed of light entirely with animated Peeps at And to tell Adam what science mystery he should tackle next, go to Adam Cole, thank you very much for this very instructive science cooking experiment.

COLE: It was absolutely my pleasure.


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