here's the lake. okay, let me try this. here's the lake. now let's suppose that lake is 10 degrees above freezing, so it's not gonna-- what's the temperature which freezing takes place, gang? - zero. - zero. okay, so if i'm gonna freeze some water, i got to bring it from 10 down to zero, yeah? okay, let's suppose out here, this is the air, let's suppose it's 50 degrees below zero. i mean, cold. and that cold air blows over the top of the lake, how many people think that cold air blowing over the top of the lake is gonna make the temperature at the surface go up? show of hands. good. nobody. how many say, that cold air will probably make the surface temperature go down? show of hands. well, almost every--like-- hey, we got everybody? does everyone think that?

have you got 50-degree-below-zero air blow over you, you're gonna get colder, not warmer? isn't that remarkable? [laugh] come on you, gang, there's nothing remarkable about that. but i'll show you a remarkable consequence of that. it turns to nine. we'll do it by incremental steps, nine degrees. the wind, eight, can you see that makes sense? where do we got to get to? zero, yeah? - zero. - okay. do anyone see something unusual here? let me ask you a question. if i take a rock and throw it in that lake, what's the rock gonna do? float. how many say, "oh, it will probably float"? [laugh]

the rock is gonna sink, man. and why is the rock gonna sink? "well, that's characteristic of rocks, just to sink." come on, why does the rock sink? 'cause it's more dense than the water, right? how about this four-degree water? what's it gonna do, gang? beginning with an s, end with an ink. sink. sink. sink to the what? bottom. the bottom. here's your four-degree water down here. what takes its place? beginning with a t. - 10. - 10. by now, it's february, okay? get the idea? honey, we're gonna need a long winter to get to that lake. but now it's march. how much time do we have?

we get--the thing, you get the idea. [laugh] what happened at four, honey? by now, it's may. people, it's may, we're running out of winter. you can't get a deep, deep lake to get all four degrees. before you can get any three-degree water, never mind zero. what are you gonna turn the whole lake to? four. and let's suppose we have like a big meteor hit or something and we get, like, no sunshine for about four or five years then we'd get something like this. you keep doing the same thing and pretty soon, after a couple of years of that, then it would all be four. honey, that's a lot of energy taken away by that cold wind. when you get the whole lake four degrees celsius,

then and only then, that's the first three-degree water that lake has seen, gang. does it stay there or does it sink? it stays there because what's down below is more dense. the lighter, the less dense will float on top of the more dense. that makes sense? watch. now we got zero-degree water. those of you who are sitting close today will see something that those in the back of the room might not see. but watch very carefully to what happens to the water at the top. [makes noise] do you see that? did you guys see that? did you see the crystals form? again. [makes noise] see, it's a little thicker? did you see those crystals form at the top? [makes noise] do you see now why ice forms at the top of a body of water?

ain't that neat? so now you start to get some ice and the ice floats on top of the other water. do you see why you have to have-- although that only happens with the shallow. you go up to lake tahoe and you take a saucer full of water, put it outside your motel room, come in and play checkers, half a game and go back there, boom, that water is solid ice. and you look out at the lake and it stays water all the time. now you'd be saying, "why?" the reason for those sort of things. how come then, like, glacier waters rapids, like some are-- is only about, like, four or five feet deep. say again, say again? how come some glacier waters like rapids is only about four or five deep. i know they're moving, but how come they don't freeze 'cause they're like ice, that's ice cold. how come moving water doesn't freeze? yeah, how come moving water doesn't freeze? well, sometimes moving water does freeze. you just usually see on the outside edges though, right by the land. you never see the whole thing freeze over. yeah. that seem like a pretty easy question to answer, doesn't it?

wouldn't you expect your teacher to be able to be, "oh, the reason for that is blah, blah, blah." well, i don't think i can give you a good answer for that other than say that the crystals can't-- they're not a good answer. can we still be friends? [laugh] oh, that did it? okay. try another question. give me one that i said i can answer. okay. hey, let's talk about this expansion and this expansion under different temperatures and everything. we got something here that's kind of neat today. ted, could you give me a hand? talk about low temperatures. ted has brought over here some liquid nitrogen. this liquid nitrogen is about 190 degrees below zero celsius, really, really cold almost 80 degrees above the absolute zero temperature. now, can we have a volunteer to jam their hand in there for about five minutes? [laughter] okay, nobody gonna do that, right?

okay, let's show how the-- let's take the-- let's show how the volume of something will change. here's an air-filled balloon, gang. okay, what's gonna happen to the volume when it gets cold? how many will say, "oh, it's gonna expand"? stand up. and what happens to the volume, gang? look at that. now, it's gonna start to warm up the air temperature. what happened to the volume? what happened to the volume when we bring it above air temperature?

hang it a little closer, ted. -- yeah. [laughter] let's try the flower. there's a flower ted found out in the ground. it's kind of nice and limp, right? kind of limp, isn't it? okay. so what happens is you slow those molecules down. why did it fizzle like that? yeah, why did it fizzle like that? what's going on? oh, gang, did you see such a thing? look at that, gang. if you stuck your hand in there and hit it against the table, would it do the same thing? yes, yes, can we have a volunteer, please? [laughter] unfortunately, it would, yeah.

another one? right. would a pen break? you wanna try it? yeah. okay, ted's got a little-- let's see if i can do this. i did this a long time ago. what was that? now, i got a friend of mine, his name is gerald walker who does something that i don't have the guts to do. gerald takes the stuff and drinks a little bit and blows out. i ain't gonna do that, gang. [laughter] ted is doing pretty good, yeah? guess who's got the courage of the two of us? come on, try one. here's where you get the bnta. what did you do? did you eat it? is it all right? did you put it in your mouth? what will you do is hold it. well, it isn't your tongue, put it over your teeth and then just blow over the top of it. i only drop, of course, i don't have any experience. i didn't say how you did that, ted. it will be-- you want me to-- oh, i have an extra one. do you want me to do it first? you do it first. let me look and see what you're doing. okay. you pick it up. yeah.

[laughter] anyone hungry? i've got one more. we'll do this at the party, gang. it's a little cool, yeah. that's why you don't stick it on your tongue for a long time but, again, the same story with the white hot spark, it's not real cold for a long time. here you go. thank you, ted. whole way, man. whole way. [laughter] okay. yeah, i've--how death defying-- going to be here. we got a penny. what do you suppose happened to the size of that penny that we put in here, gang? if you had some calibers, you measured the diameter, what would happen to the diameter when it's cold, get larger or smaller? smaller. smaller. they'll shrink, right? is that water warm after a while it's been out in the air?

oh, it's not water. this is liquid nitrogen. yeah, liquid nitrogen. oh, darn. does it warm up though after? oh, yeah, it's warmed up. it's boiling. it's boiling right now. that's what this stuff is. it's boiling right now. do you want to see if this gonna break, right? no. that's gonna be-- so that's a little real. now, do you want this back? we're gonna make our own. [laughter] copper is a very good conductor. does the-- so when we cool things, gang, they expand or they contract? question. isn't that plastic container? yeah. is it brittle? yes, it is very brittle, very brittle, yeah. see the frost in the outside? if you ever drop that, it will probably just crack. hey gang, i want to leave you with a question. when we cool things, they contract. right. when we heat things, they expand. if i heat this ring, get it really, really hot--

and i'm gonna do that next time. next time, i'm gonna put it under the blowtorch and i'm gonna get it really, really hot. would it become larger, smaller or stay the same? let's suppose we did this as a test. i took the ring and let's suppose the ring right now will pass through the-- let's suppose the ball will pass through the ring. if i heat the ball up, will it still pass through the ring? no. that's elementary. i would insult you if i told you to think about that for a long time, right? we know the ball is gonna get bigger. and if the ball gets bigger, it will never get through the hole if it just barely makes it now. isn't that true? here's the question i got for you. the next time we come in, i'm not gonna heat up the ball. i'm gonna heat up the ring. and when i heat up the ring, will the ball be able to get through if it just gets through now? will the hole become larger, smaller or stay the same size

when i heat the ring? think about that 'cause we got that for homework. hey, you know what? you can do this as a test, experiment. take a ring off your finger, put it on the stove, get it hot. does the hole get bigger, smaller or stay-- and then jam it back in your finger and see. [laughter] no, no, not your finger, your kid sister's finger, all right? and see if the hole gets larger, smaller or stays the same and see if you can say hc for next time, gang, okay? homework? as a homework. catch you later, physics. [music] captioning performed by aegis rapidtext