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Frostbite Theater


Cups full of water are placed into bowls of liquid nitrogen! Which cup will insulate the best?

Announcer: Frostbite Theater presents... Cold Cuts! No baloney!

Joanna and Steve: Just science!

Joanna: Hi! I'm Joanna!

Steve: And I'm Steve!

Joanna: And this is a container of liquid nitrogen!

Steve: And these are two plastic cups!

Joanna: Let's see which cup is the better insulator!

Steve: Okay! So, um, how do we do that?

Joanna: Well, we'll pour water into each of the cups and then we'll pour the liquid nitrogen into each of the bowls. If we then place the cup in the bowl, the heat from the water will try to pass through the cup into the liquid nitrogen. Since we know that insulators don't allow heat to pass through them that well, the water inside the cup that's the better insulator won't freeze as quickly.

Steve: Okay. Well, I just happen to have a container of water right here. So I'll just pour some in and we can get started!

Joanna: Um, actually, in an experiment, you only want to change one thing. The fancy term that scientists use is "independent variable" or "manipulated variable." So, we're already changing what the cups are made out of, so...

Steve: So... we need to have the same amount of water in each cup?

Joanna: Exactly!

Steve: So, I need to measure the water?

Joanna: That would be nice!

Steve: Oh! I was wondering why we had this thing back here. So let me pour the water back into this. And, what do you think? 50 milliliters sound good?

Joanna: Yeah, that sounds about right. Okay.

Steve: So that's 50 milliliters of water for you.

Joanna: Thank you!

Steve: You're welcome! And... 50 milliliters of water for me!

Steve: Well now wait a minute. If I had to measure the water, don't you need to measure the nitrogen?

Joanna: Well, yes, but I'm just going to fill each of the bowls to the top.

Steve: Okay, well, that sounds fair.

Joanna: All right, are you ready?

Steve: Yes!

Steve: Well now wait a minute. Don't we need to keep these in there for the same amount of time also?

Joanna: Yes, we do. Since we're changing what the cups are made of, we want to keep everything else the same. Now, scientists have a term for that as well. They call the things that don't change "constants."

Steve: Oh!

Joanna: All right! 3... 2... 1...

Steve: Mine's going kind of nuts. What's yours doing?

Joanna: Not too much. Yours is really fogging up.

Steve: Actually, I'm getting a little bit afraid of mine right now.

Joanna: Yeah, mine's not really doing too much.

Steve: Is it time yet?

Joanna: Yeah, I guess we can take them out.

Steve: Well now wait a minute. We both started off with the same amount of nitrogen in each bowl.

Joanna: Right.

Steve: But now mine only has a little bit of nitrogen. But yours, yours has a whole lot in there!

Joanna: And not only that, what's inside your cup?

Steve: Whoa, there's ice in my cup.

Joanna: How much?

Steve: I have no idea. But, wait. I started off with 50 milliliters of water, right? And now... I have 32 milliliters of water. So if I started off with 50 and now I have 32, that means 18 milliliters of water froze and changed to ice. That's 36 percent of my water!

Joanna: That's a lot!

Steve: That's a lot of water! How much water in yours turned to ice?

Joanna: Let's see. Well, I also started with 50 milliliters of water and... What do you know! I still have 50 milliliters of water left! So, which cup's the better insulator?

Steve: Well, since none of your water froze and a good chunk of mine did, your cup must be the better insulator. And that must also be why I had less nitrogen in my bowl when we took the cups out! My cup's not a good insulator, so the heat from the water past right through the cup and went into the nitrogen. So my water lost heat and got colder and started to freeze and the nitrogen gained heat and boiled faster!

Joanna: Exactly!

Steve: That's right?!

Joanna: Yeah!

Steve: Wow!

Joanna: Thanks for watching! I hope you'll join us again soon for another experiment!

Steve: Ah! It's refreshing!

Joanna: Icy!

Steve: Yes!

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