Cracking The Egg Sprinkler Mystery

If you spin a hard-boiled egg in a pool of milk, the milk will wick up the sides of the egg and spray off at the egg's equator. Engineer Tadd Truscott, of Brigham Young University, launched an investigation to figure out why this happens ? complete with a custom-built spinning apparatus, billiard balls and high speed video cameras.

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IRA FLATOW, HOST:

Up now, our Video Pick of the Week. Flora Lichtman is with us. Hi, Flora.

FLORA LICHTMAN, BYLINE: Hi, Ira.

FLATOW: What have you got for us this week?

LICHTMAN: This week is an experiment that anyone can do at home. You just need permission from your housemates.

(SOUNDBITE OF LAUGHTER)

LICHTMAN: So here's what you do: Go to the refrigerator, get out some milk, and then pour a puddle of it on your countertop or your kitchen table. Then take a hard-boiled egg and spin it in that puddle.

FLATOW: That's it?

LICHTMAN: That's it. That's it. That's it. We're done.

FLATOW: You don't have to cry over this spilled milk. You're going to spill it, and then...

LICHTMAN: No tears for this one, no.

FLATOW: No tears. And you're going to take a hard-boiled egg and spin it in the milk.

LICHTMAN: And here is the amazing thing that happens. The milk wicks up the side of the egg and spins off at the equator, and it looks like a little mini-sprinkler. And this experiment came from an engineer, Tadd Truscott, who's at Brigham Young University. And, you know, as we talked about this this week in our editorial meeting, you may remember that there was some skepticism in the office.

FLATOW: You mean the guffaws that were sure...

LICHTMAN: So much guffawing.

FLATOW: What have you got next week?

LICHTMAN: Yeah. Where the heck did this come from, I think was the question posed. So I...

FLATOW: Very euphemistically put, Flora.

(SOUNDBITE OF LAUGHTER)

LICHTMAN: Thank you. Well, this is radio. So, anyway, I tried to track this down. So I talked to Tadd about this, where he got it, and he said that it dates back to his grad school days.

TADD TRUSCOTT: One of my favorite people I ever met at MIT was Alex Hornstein, and he just has a lot of wild and crazy ideas. And one day he was like, oh, we should spin an egg in milk. And I was like: What? I took some video of it, though, and suddenly we were like, wow, now that is something to behold. It's really quite beautiful to watch this milk rise up the side and flick off the edge. So that's kind of where it was born.

FLATOW: OK. So that's the first part. And we get some clue there, but I don't know. I - you probably don't feel satisfied. We didn't really get to the bottom of it. We heard about Alex Hornstein, but I thought I've got to give this guy a call. And he happened to be in Hong Kong, but he was available from Skype. So I gave him a ring.

(SOUNDBITE OF TELEPHONE RINGING)

ALEX HORNSTEIN: Hey, Flora.

LICHTMAN: And I asked him if he remembered that fateful day in the lab when they spun the egg in milk.

HORNSTEIN: I do. We had just gotten an expensive, high-speed camera for the lab. We worked in a lab where Tadd shot curveballs into a giant tank of water, and this was somehow important for science. And so we got this giant, high-speed camera that was, like, hugely expensive. And so we thought we should mess with it.

And so we started picking up things that would be, like, really funny in high speed. And so we put ourselves in this, like, 600-gallon tank of water and swam around and filmed that. We shake our faces in front of the camera, and we'd watch our lips get really distorted.

And in high school, I had a teacher who was really into high-speed photography. I was his work service student, and so I used to build him high-speed photo systems, and he had done a whole series with eggs and milk. But I thought, oh, that'll be cool. We should take some of these egg photos.

LICHTMAN: And so I went on to ask Alex where he thought his high school teacher - that's where the investigation stopped, by the way. But I asked Alex where he thought his high school teacher got this, and he said that it was his impression that the people in this sort of high-speed video and high-speed photography communities had come up with all these neat things to look at. Anyway, if Alex Hornstein's high school teacher is listening to this and has an answer from where this came from, email us and let us know.

But in any case, the bigger sort of mystery is, why does this happen? And Tadd Truscott sort of took this up again years later because he was doing this experiment with his kids in the kitchen. And he realized they didn't know what was going on, and he has a PhD in hydrodynamics, so this is something he thought he could tackle, which is what he did. He built this custom-made spinning apparatus in the lab, and then he spun all these different things, like billiard balls and this big, metal ball and all kinds of stuff, in different fluids. And that's the video - we sort of have a montage of that on our website.

FLATOW: And it's really amazing. I mean, just so we repeat for people, if you take a - spill some milk on a counter. Take a hard boiled egg, and you know how it can spin on its point? As it's spinning on its point, the milk rises up off the counter on its own, almost magically, right? And then get spun out this side, and it gets spun out at a very high rate. Didn't he calculate how fast it could get spun out there?

LICHTMAN: Yeah. I mean, you know, they looked at different things, and I think it was four liter - you know what, actually look at the video because I don't want to misquote it, but it was a pretty good pump, it turns out. That was a kind of, you know, (unintelligible) for Truscott.

FLATOW: Yeah. And so he - so the video shows not only the egg but it shows an eight-ball, right? A cue ball, an eight-ball spinning in the air, and then the milk is coming off, and he tried it with different fluids in the video. He found out which one works the best?

LICHTMAN: Yeah and - well, it turns out that if you use different fluids of different viscosities, you'd get different shapes flying off. So if you use, like, a glycerin water mixture, which is way more viscous than water, you can get these sheets coming off of your spinning cue ball that are like feet in diameter. I mean, it's really cool to watch.

FLATOW: Wow. It is. It's our video pick of the week up there, you know? Maybe if you've done this yourself, Flora, would you like to see some video?

LICHTMAN: Oh, definitely.

FLATOW: I knew you would.

LICHTMAN: Of course.

FLATOW: You can send us your videos. And why this happens and also the explanation why this happened.

LICHTMAN: There is some science in this video, you should say. I mean, we haven't touched on it here.

FLATOW: We're not gonna give it away. You have to go watch the video.

LICHTMAN: Watch the video, but it's a really simple, elegant explanation. It's pretty neat.

FLATOW: Elegant is a good word for it. Up on our video pick of the week on our website at sciencefriday.com. You can also download it on our iTunes on your cellphone or smartphone that way too. Thank you, Flora.

LICHTMAN: Thanks, Ira.

FLATOW: I'm Ira Flatow. This is SCIENCE FRIDAY from NPR.

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