Liquid Nitrogen and the Tea Kettle Mystery!
Everyone knows that liquid nitrogen is cold and everyone knows that tea kettles whistle when they're hot, so what's going on here??
Announcer: Frostbite Theater presents... Cold Cuts! No baloney!
Joanna and Steve: Just science!
Steve: Okay, it's not that hot, not that cold. It's sort of room temperature metal, so it's kind of cool.
Pretend I'm at home. I'm at home, my radio is broken. No music. The only music I can get is if this thing whistles, which isn't that exciting but it's better than nothing. How do I do that, at home?
Audience: Heat it up!
Steve: Yeah, I go to the kitchen, I fill this up with water, put this on the stove and, for this to whistle, this has to get...
Steve: It's got to get hot. Do I have a stove here?
Steve: No! Can I make this whistle?
Someone in the Audience: Use the liquid nitrogen!
Steve: Okay! Sure! We'll try that!
Instead of filling this up with water, I will put a few precisely measured and accurately delivered spoonfuls...
Of nitrogen into the tea kettle.
So now, inside the tea kettle, I claim this thing is now 321 degrees below zero.
Is that hot or cold?
Audience: It's cold.
Steve: Does it sound hot or cold?
Tea Kettle: -- Whistling --
Audience: Hot! Hot!
Steve: Yeah... Uh, right. Okay. I'm confused. Let's take a vote.
Who says "Tea kettle hot!" raise your hand.
Who says "Tea kettle cold!" raise your hand.
Who says "I've got not idea..." raise your hand.
Okay, it's perfectly fine not to know. That's why scientists do experiments. They do experiments because they don't always know the answers.
So, easier question. What's this?
Audience: A glove!
Steve: A glove. I'm going to take the glove and wipe it on the tea kettle.
What do you see on the glove?
Steve: Frost. Ice. This thing is cold enough we can take the water vapor from the air and we can freeze it to the surface of the tea kettle. Okay, so this thing is really, really cold. Can I have a volunteer please? To lick this.
What'll happen if you lick it?
Yeah. What movie was that? That was Christmas Story? Yeah.
So here's what I'm going to do. Rather that have somebody lick it for real, getting the lawyers involved yet again, I'm going to take the glove, I'm going to carefully take a little bit of water from the flowers and pour a little bit of water on the glove.
And clean up the little bit that I spilt.
And I'll carefully put the flowers back so they don't get hurt.
For those of you that have had literature, that's called foreshadowing.
Now, what we've just made is a model of your tongue. It's wet and it's floppy like your tongue is, it's just blue with fingers, right, close enough.
So, everyone who wanted to lick this, pretend this is you.
Okay, so here you come to the tea kettle going 'La, la, la, la, la, la.'
Everyone go 'La, la, la, la, la, la.'
Audience: La, la, la, la, la, la.
Steve: And you lick the tea kettle.
Now, that's going to be fun for, like, two seconds. And then, you're going to want to get your tongue back. So, what do you need to do? You gotta pull it.
Steve: So there is ice on your tongue. Here are little bits of tongue on the tea kettle. So, not a great thing to go around and lick. But, there's a problem. You guys told me this whistles when it's hot. Why was it whistling if it was cold?
Yeah, how does a tea kettle work? It doesn't work if something's hot.
If I'm at home, I'm at home, this is full of water, it's on the stove, it's whistling, what's that mean the water inside's doing?
Someone in the Audience: Boiling!
Steve: Boiling! When a liquid boils it changes from a liquid to...
Steve: A gas! The gas takes up more room, comes out of the hole, makes this thing whistle. Tea kettles don't tell you if something's hot or cold. They tell you if something is boiling or not. So, if I take the nitrogen and shove it in here and it whistles, what does it mean the nitrogen's doing?
Steve: It's boiling! It just happens that it boils if it ever gets warmer than 321 degrees below zero. What in the room is warmer than 321 degrees below zero?
Steve: Everything! Everything in the room is about 400 degrees too hot for this stuff to stick around. So, if the nitrogen touches anything in the room, it boils, changes back to a gas, goes into the air and we end up breathing the stuff.
Have you ever taken water and flicked it on a hot frying pan? And the water kind of dances around? Does the same thing on the table. When we pour it on the table, it hits the table, it boils, and then it floats on a little layer of gas. So the table's not wet. And if I want to get rid of the nitrogen faster than having it roll off, I just introduce it to mister glove. And I can boil it off a lot faster that way.
This is what the stuff looks like. It looks a little like Sprite. I wouldn't go drinking it. Why is it bubbling?
Audience: It's boiling!
Steve: It's boiling! The air around it is 400 degrees too hot for it to stick around. If I touch it with my glove, it'll boil faster. Don't know if you can see that or not...
If I put it on the overhead and Mr. Dave hits the lights...
So, that's what it looks like. It looks kind of like boiling water. It acts kind of like boiling water. But it's not boiling water. It is boiling.
But boiling doesn't mean hot. Boiling doesn't mean cold. Boiling just means you're changing from a liquid into a gas.
Now, keeping in mind that this stuff is very cold, even though it's boiling, I'm going to need from the audience, two somewhat brave and slightly foolish volunteers!
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