put yourand in front of your mouth and with your mouth open, so when you breath-- so the air doesn expand, i want you to blow. a little disruption right there. okay now bring your mouth down really tight, so the air expands when it comes out. notice any difference in temperature? yeah. try it again, gang. open mouth. open mouth. now close mouth, so the air expands. okay, you wanna see that more dramatically? watch this. here's some steam here, huh. would i dare to take this glo away? yeah.

yeah, easy, easy saying that no proem. hot or cold? begin with a c. it's cool. relatively cool. hc? i'm not gonna put it way down at the zzle. it turns outhat that which you are seeing here, gang, is not steam. at which you can't see, that's the steam. but wh does that steam do? begin with the x. - expand. - expand and when it expas, what's it do? ben with another c. - cools. - cools. and that's your evidence over right there. isn't th remarkable? so try this at home, huh? it's cool to the touch and that gets hoer, hotter, hotter, hotter, but up here it's relatively cool, cooler here than out here. i wonder if there's a reason for that. how many say, "well, no, there's obablyo reason

"for that. it's just one of those little flukes of nature"? and at's what we're gonna be talking about. what was the reason when you bw like that it was hot and you went like that it was cool? and did you notice it was appreciably cooler doing that? that's because the air had to expand. now, we can understand that iwe thi small. here's a molecule moving around. it's gon h its nghbors, right? sometimes it gonna hit a neighbor and bound off with more energy. sometimes it's gna hit a neighbor and bound with less energy. now, when does it gain and when does it lose? look at this ping-pong paddle i have here. see it? watch this ping-pong ball come in and hit the paddle. watch this. watch this. [makes sound] see, it went off with the same speed? i could've held this very rigidly. watch again. [makes sound] kinetic energy in, kinetic energy out, same, same. did you see that? this time, i'm gonna move the paddle up like this. now watch. [makes sound] did you see it move away faster? why?

'cause i hit it. i belted a hand, it came in. boom. i gave it energy. when you got a pump and you're pumping air... [makes sounds] ...do you ever reach down and reach and touch that pump? [laughter] that pump is what? - hot. - it's hot. why? 'cause you have belted those molecules. what do you have when you take a ball-- a baseball bat and start hitting balls? what are they gonna do? slow down? they're gonna speed up. and so what happens, that paddle comes in and-- now, what happens in air when air molecules movin' by and it hits-- and it sees another one that's coming toward it? ba-ba-boom. it could bounce off with more energy than it started with. this one would slow down. but that can happen. as we see with the paddle coming in--ba-boom. it goes off faster than it came in. how about the converse? let's suppose my paddle is going away. and now my ball hits... [makes sounds] see that? shall i do it again? okay. it dribbles down. it loses speed.

so if molecules will hit others that are going away, will they rebound with greater speeds or lesser speeds or is this not clear? lesser speeds. can you see it's lesser speeds? lesser speeds, gang, okay? so what happens when air expands? go right down in there, in the microscopic realm right there, and take a look, and what do you see? "hey, now, where are you guys goin'?" they're all goin' way, yeah? and you're a molecule right in there. now you're gonna bound off all those guys. and when you bound up, you pick up speed or lose speed? - lose speed. - you lose speed. that speed goes out to the air. all that energy spreads out. in there, you've got less energy. it's--you put a thermometer-- it's--you--right here. it's really cooler. it's cooler when it expands. does that have a lot to do with weather or not? a lot to do with weather conditions. expanding air will chill, will cold, will become colder. neato? can you see why?

pretty neat, huh? yeah. so you're at the top of the mountains, honey, you know why it's so cold up there. that air has been expanding. and when it's been expanding, of course, it's cold up there. it's a lot closer to the sun. no, no, that expansion rate, that expanding of that air cools it a lot. so actually when you heat something, it expands and you happen to put more energy into it because the--for expanding, too, to heat it up? oh, now, we can get a little mixed up here. it turns out that when you heat some air, like you heat anything, you will make it grow. you will make it expand. okay? so you can force something to expand. i can take a balloon of air and hold it over a stove. and it will expand. okay? we're not talking about that. it doesn't follow now that expanding things-- --not gonna change or-- well, that--now, to say that you can heat something up and make it expand is one thing. but now we're saying if the air will expand by itself, push outward, when it expands, what happens to the temperature in the middle of that?

drop. and that drops. so the reason for it expanding is because it was going from a region of higher pressure to lower pressure? excellent, excellent, excellent. the reason it expands is because the air goes from a region of high pressure, down here, deep, deep down in the bottom of this ocean of air. and when it rises, what's it gonna do? like the balloon, like the fish, like the scuba diver we've all talked about-- these ideas are all connected, gang, huh? and as it goes up, up, up, it's gonna expand. and we learned a new thing today. as it expands, son of a gun, it cools. why does it cool? because the molecules in the middle are making impact with things on the average that are going away. and so they rebound with less, less, less speeds. and the effect is big. i mean, it's quite noticeable. there's a third form of heat transfer, gang. and the third form-- not conduction, not convection but what? radiation. radiation. that's right. radiation. and heat radiates from the sun. and it gets to us by the process of radiation.

we're gonna talk about that a lot later on. we've talked about electromagnetic theory, and we talked about light. but i wanna talk about one aspect of that now. and that one aspect is is that the frequency of that radiation is directly proportional to the temperature of the source. why i want you to know about that is because i want you to know a little bit about what people are talking about when they talk about the greenhouse effect. you've all heard about it: the fact that there's a layer of carbon dioxide in the world now that is holding in the heat, and the earth is becoming warmer and warmer as the years go by, at least that's the idea. i want you to understand that. and to understand that, we have to consider a formula. now the formula makes sense, kinda. it just says that the frequency of radiation is directly proportional to the temperature of the source.

let me give you an idea. you see this rubber tube i have, stretched out and connected to the wall over there? can you all, guys, see the rubber tube? what color is the rubber tube? - yellow. - green. can you guys all be lookin' at the same rubber tube? what color is the rubber tube? - blue. - green. well, take your pick, all right? put on your glasses. so we got a rubber-- it looks red to me. yeah, it's a red rubber tube. you guys see the red rubber tube? now i'm gonna shake the tube. [makes sounds] what do you guys be seein' across the room? waves. ain't that right? can you see the waves? now i want you to look at what happens to the frequency of the waves when i shake it faster. how many see the waves shakin' up? [makes sounds] how about when i shake it like this? what's the frequency of the waves? [makes sounds] it turns out that the faster i shake, the higher the frequency of the waves. is that far out or not? that's not far out at all. that's common sense. you shake a thing like this... [makes sounds] ...you get long, lazy waves.

if i shake it like this... [makes sounds] ...i'll get little, short waves like that. we'll learn about that later, okay? that wavelength, frequency. it turns out-- well, i won't even talk about wave under this point. let me just talk about frequency. that sun: high temperature or low temperature? high. the earth: relatively, high or low? low. now it turns out that everything is emitting waves: you and me and everything else that has a temperature above absolute zero. everything is emitting waves, and everything is absorbing waves. we're just gonna concentrate on the sun and the earth for now 'cause we're running out of time. the frequency of waves emitted by the sun are very, very high. the sun's temperature is like this. so the frequency of waves is like that. so high, millions of billions of cycles per second. [makes sounds] and we call that light. and that's--and light carries energy. electromagnetic energy. high, high frequency.

why is it high frequency so high it's called light? because the temperature of the sun is very, very high. okay? now that light comes down and... [makes sounds] ...hits the earth. and so the earth warms up. but the earth reradiates that energy back out. but what frequency: high or low? low. why low? because the temperature of the earth is like this. and so the frequency of radiation that's emitted is like that. that's way down below the threshold of the red in the color spectrum. we call it below red. in a physics class, you'd never say below red. in a physics class, you'd say what, gang? infrared. so it turns out the sun emits visible light, high frequency, and the earth emits infrared, low frequency. now it turns out different things, different materials are transparent to different wavebands or frequency bands.

it turns out the atmosphere of the earth is transparent, very, very nicely to visible light. of course, it is. you can look up and see the sun and the stars right through it. we have a transparent atmosphere for light, high frequencies. it turns out the atmosphere, especially if it has little water vapor in it, is terrible--is a terrible-- well, not terrible but it's a much less transparent material and medium. so what happens to us, gang, is this. this is the sun up here. and the sun is emitting very, very high frequency rays. they come right through the atmosphere. and the earth radiates low frequency, and they can't get through the atmosphere. a lot of them can, of course, but a lot can't. and those that can't then, this energy starts to pile up in here. this happens in your car. you leave your car out in the parking lot, gang, okay? why is it when your car out in the sunlight is so hot when you open the door? well, you can say, "well, 'cause there's heat.

it's been heating in the sun." but let's look a little carefully. that sunlight is comin' right through that window, high frequency, right through the window pane. and what it does, it hits the inside of your car and heats it up. and the inside of your car reradiates. now if the inside reflect it, you'd be okay. that's why you put that silver stuff on your windshield. that's gonna reflect the light. and that reflected light-- it turns out reflected light doesn't change its frequency. we'll learn later on if you're wearing a blue shirt and you stand in front of a mirror, guess what color your image is, gang? son of a gun, blue. now you put on a red shirt and you stand in front of a mirror, what is it? whoa. same shade of red, okay? it turns out that reflection doesn't change frequency, but reradiation does. 'cause you catch it, reradiate it from one source and reradiate it from the other source, honey, you get different frequencies. and that's what's happening with the greenhouse effect. it reradiates a frequency that can't get through, especially that carbon dioxide. and that's holdin' the energy in.

you kinda be seein' that? important stuff. okay, more physics next time. yay. [music] captioning performed by aegis rapidtext

welcome to another session of beliefs and believers. today we're going to be looking at ritual and symbol and getting some more specific information on those key, key points. we mentioned that myth and ritual, of course, are packed with symbols, and we talked about symbol - if you can remember way back to the start of semester, we were talking about where people got symbols from and they draw them from the most common area. well, today we want to look at types of symbols and how symbols work as a powerful force within the myth of ritual. but we have a little time today because we've just got notes,