Calls again and again and you say, i dont know what to say but im just too busy. Im just too busy with my work. And he say over the phone, oh, thats too bad because im into giving massages and i have to do a onehour continuous massage. Massage . Well, maybe i can find the time. Come on over, right . So they come over and they gave you massage and they pour some alcohol on your back. And when they pour the alcohol on your back, you, oh, wow, its cold. He say, no, its not cold. I got it from the medicine cabinet right where all the other stuff is. Is that alcohol colder than anything else in the room . No. No. If it were, what would happen . Thermal equilibrium. The other things would heat it up. Isnt that true . Doesnt heat flow from high to low temperature . And arent all the things in our environment here, arent this, this, this, all these things the same temperature . What if this book were hotter . What would it do to the table . Energy would cascade from the book to the table until they both became the same temperature and they will level off. So that alcohol thats poured on your back has the same temperature as anything else around, but it feels cold. And why does it feel cold, gang . Because what is that alcohol doing . What its doing is what were gonna be talking about today. Its changing state. Its changing from the liquid state to the gaseous state, okay . And we call that what . Begin with ev . Evaporation. Evaporation, thats right. And were gonna be learning that evaporation is a cooling process. You know, sometimes youre swimming and you come out and youre all wet, a little breeze come by and you feel kinda chilly. But if no breeze comes by, you dont feel so chilly. And whats going on . When that breeze comes by, what happens to the water on your body . Evaporates. It evaporates. When it evaporates, how does your body feel . Begin with a c. Cool. Cool. Now, were gonna ask the question hc. Why is it that evaporation is a cooling process . And we can reason that out if we think small. See this glass of water here . Do you think all the water molecules in that glass are moving at the same speed all the time . How many say, oh, yes. At exactly the same speed all the time. Stand up. Nobody. How many say, well, theres a whole distribution of speeds and the average that relates to that which we call temperature . Show of hands. Yay, we got the idea. But you have all kinds of speeds in there, gang. Youve got fast ones, youve got slow ones. Youve got some at absolute zero in a moment [makes sound] when it comes to a dead halt, boom, that corresponds to absolute zero. The next minute, something hits it, bam, bam, bam. Theyre moving in all kinds of speeds. So you got a distribution of speeds. And the distribution goes Something Like this. Its like the distribution of our test scores. Remember how your test scores were . Score, numberno. Here was the score here and the number of people getting the score . Well, the same type of thing here. This would be the temperature or we could say the motion or the Kinetic Energy. The Kinetic Energy of molecules in a glass of water versus the number of molecules. And whats the graph just say . That down here, theres a few that are going slow and theres a few that are going fast. These are relatives ideas here, huh, relative values. And most are going right about here in the middle. And when you talk about the temperature of the water, youre talking about the average Kinetic Energy, what most of these things are doing. Isnt that true . Now, which of those molecules do you think, in the glass of water, would be most apt to evaporate, the fast ones or the slow ones . Fast. Fast. I remember when i was a little kid, my father would drink his coffee and it would be too hot to drink, hes gotta go to work quickly. And what hed do is hed take the coffee and then pour it on a saucer. Hed lift up the saucer and drink from that. It used to get my mother annoyed. She says it wasnt proper. What do you mean proper . He was using physics. Why did he pour it on a saucer to cool it, gang . Oh, you dont be knowing . Well, it turns out evaporation is guess what kind of phenomenon . Surface. Surface area. The more surface, the more evaporation takes place. If i take a glass of water and set it here, itd take a long time for you to see the level go down. If i take that glass of water and spread it over the top of the table to increase the surface, by the end of this lecture, that water will be . Begin with a g. Gone. Gone, okay. It would evaporate because thered be more surface. All my father did was increase the surface area. And when he increased the surface area, he gave what kind of molecules the chance to get out . Fast or slow . Fast. Fast. Fast ones leave. And when the fast ones go out into the vapor state, whats left behind . Relatively slow. And so your most energetic molecules are gonna leave and thats gonna push the peak down cause the slow ones wont have the fast ones to bump into anymore. And its not like there are some that are always slow and some that are always fast. These are all water molecules, the same mass. So the slowest at one moment might be the fastest at the next moment. Theres a continual chaos of motions in there and its always completely random, random that peaks out at some particular average. And when you take the faster moving and have them escape to the air, it stands to reason the slower moving are left behind. So thinking small, we can see why evaporation is a cooling process. This is one of the things that makes sense, yeah . Any questions in this . I saw a nice example of this when i was in india some years ago. I was in khajuraho, india. It was really hot, like 110 fahrenheit. And i was trudging through and all of these people are out in a field. And theyre all doing work out there, working in the field. In a corner of the field was a kid, a young kid. He must have been eight years old or so. And that kids job was to continually keep a great, big clay pot of water cold. And how he did that is he had a gunny sack over the pot. The pot was open like this. He had a gunny sack over like burlap, yeah . And he had a little pot down here and a long stick with a gourd in there. And he would just keep making sure that the gunny sack stayed wet. And as long as he kept the gunny sack wet on that hot day, honeys, the water inside was begin with a c and i aint saying cool. Cold. Cold. Hc. Be checking your neighbor. You see how that works, gang . You see how that works . That gunny sack, water is evaporating, right . Which water molecules are evaporating, the fast or the slow . Fast. Fast. The fast. Whats that leave behind . Slow. Slow. So the gunny sack then gets a little cooler than the outside. But the gunny sack is against the clay and the gunny sacks are a little cooler than the clay. Which way does energy go, from the clay pot to the gunny sack or the other way around . Clay from the clay pot to the gunny sack. Heat flows from High Temperature to low of itself, yeah. And so, what happens to the gunny sack i mean, the pot gives its energy to the gunny sack and that keeps going off, off, off. You see what im saying . And so, the pot gets cool, cool, cool, but the pots against the water inside. Now, if the pots cooler than the water, and the pots against the water, which way is the energy flow gonna go, gang . From the water to the from the water to the pot. And so you see, so long that he keeps having the fast moving molecules leave on the outside, hes cooling the water on the inside. Thats beautiful physics. Let me ask you a related question. Why do hot dogs pant . Seen a hot dog [pants] go like that all time. All time, get the tongue out. Why . Do you know hot dogs pant . The answers simple, no sweat. Dogs dont sweat. The only place dogs sweat are in between the toes. But intheir body, they dont sweat, so they have to evaporate to cool. Where do they do that . Right inside where it counts, right down to the bronchial tract. [pants] theyre evaporating from the tongue and the mouth and right down through there. So theyre getting a nice, nice cooling. And on really hot days, why do you see a dog goin [pants] like that, okay . Maybe trying to get the wind going through here. Im kidding about that. [laughter] why do the pigs roll over the mud . Because theyre dirty creatures. Come on, come on, why . They dont sweat. They wanna again, no sweat, see . And they wanna keep they wanna get wet. And how do they get wet . Get wet wherever they can. And they get wet and when the breeze come by, evaporation. Evaporation does what to them . Begin with a c. Cools. It cools them. Hey, hey. Natures thermostat. Us, when you overwork, you guys start to sweat. Can i say sweat . All right, perspire. We startits a little more refined, right . We perspire. Now, why do we perspire . Natures thermostat. Isnt that true . Natures thermostat. The harder you work, the more you tend to overheat, the more you sweat. And the more you sweat, the more you cool. Cool. Begin with ev. Evaporate. Evaporate and release the the perspiration in your body evaporates, yeah . And when that evaporation takes place, whats that do to the skin, cool it or warm it . Cool it. Cool it. And so you feel cooler. Aint that neat . Ill tell you where that short circuits out. Do you ever stay in a hot tub too long . Yeah, its bad. I remember way back in the seventies when i it used to be common back then in San Francisco in the seventies to go hot tubbing. You guys, when you meet someone new, you go to a movie or something, right . [laughter] i remember one time, this lady, i asked her out, asked her to go to a movie. Says, why dont we just get to know each other better . Why dont we go to the Grand Central hot tubs . [laughter] i dont know her yet, you know . I have thismy fondest dreams went a little bit too fast. Can i handle this . You know . Its a true story, by the way. And soyeah, we went to the hot tub. Hey, and in the hot tubs, all my students were there. Hey, what are you doing here . Hey, mister hewitt, what are you doing here . [laughter] hey, hewitt. Hey, that checkyourneighbor routine worked, didnt it . Hey, all right. But, anyway, i got in the hot tub there, and its really, really hot, yeah . And im in there, and shes outside, and she says, come on here, letscome over here, ill give you a rub down. Oh, ill just stay in the water here a little longer. [laughter] that waters hot. And that water is hot, and guess what im doing inside that tub. Sweating. Sweating like mad. Oh, yes. But the sweating, usually, it corresponds to begin with ev. Evaporation. Evaporation. And evaporation, usually cools. Cools you. But im in the water. And whats happening there, gang . Any cooling going on . No. So what does the old thermostat up here say . M s, m s, m s. More sweat. More sweat, more sweat, more sweat. So im under the water sweating, sweating, sweating profusely. My heartboom, boom, boom, boom, boom, boomoverworking. I interrupted my bodys natural function by getting in that hot water and preventing the evaporation doing the cooling. And, honey, if you wanna get wasted, talk about limp city, you will really get wasted if you stay in the hot tub too long. And you think sometime, people thinking, oh, you come out, hey, hey, man, hey. No, its not that way. You come out [makes sound] [laughter] youre all wasted. Youre all drained out. If youi wonder, too, about these deodorants, you know . You put these deodorants on that make it so you dont perspire . Can those be good for you . That mean youre gonna overheat. If you prevent natures function, sweating, youre gonna overheat. And if you overheat, your heart overworks, and, honey, you get wasted, not energized. Just the other way around. Kinda makes sense, huh . Hey, if evaporation is a cooling process, how about boiling . Oh, no, boiling wouldnt be a cooling process. Boiling is a heating process. Oh, no, no, no, boiling is a cooling process. Dont believe it . You come home sometime, your hands are all hot and sticky, you wanna cool them off. Your moms over there cooking a great big pot of boiling water ready to put some spaghetti in. You read in the book, boiling is a cooling process. What do you do . You take your hot and sticky hands and you dunk them into boiling water. You mother says, what are you doing . Im cooling them off. Good idea or bad idea . Bad. Bad idea. So is boiling really a cooling process . End with a p. Yup. Begin with a y. Yup. Yup. Yet the question is begged, whats heating and whats cooling. Yes. Tell your friends that when youre cooking some tea and youre boiling some water, and they come by, say, what are you doing . Oh, im cooling off the water. Theyll say, youre what . I say im cooling off the water. And they look at it and see all the bubbles coming out. Youre cooling the water . Say, yeah, im cooling the water. Put your hand above. Ooh, i burned myself. You know why you burned yourself . You say, because heat came from the water. Thats what i mean by cooling. See, i got the fire underneath, thats heating the water. Thats the part thats heating the water. But the boiling process does what . Cools the water. Honey, the boiling takes away all the energy. To say you take energy from something is to say you cool it. If redhot lava is coming down the mountain and it cools, does that mean its cold . No, but its cooling as its coming down. And your boiling water is cooling as it boils. Isnt that neat . Thats why i use a Pressure Cooker. Use a Pressure Cooker to prevent the boiling. That will prevent the cooling, and that will allow you to get more heat, more internal energy in your water and cook your food faster. Thats what its all about. Because more pressure lets look at that. Heres regular boiling. Lets not look at Pressure Cooker yet. I wont put the lid on, okay . This is just regular boiling. Lets use whats the temperature at which water boils, gang . 100 degree celsius. Is it 100 degree celsius . Is that right . Lets suppose we get to 98 degrees celsius. Now the water molecule in there, theyre going a lot faster than they were at 78 or like that. Isnt that true . Okay, now, theyre 98. Now, those water molecules are all banging around in there. A little group of them says, hey, gang, lets cut out, lets form a little bubble. Lets be buoyed to the top, and lets cut out. Lets steam it out right now. And so what they do is they form a little bubble here. And you know what happens when they form that little bubble . 30 kilometers of air, honey. 30 kilometers of air are squashing down. Squash right down and smash that bubble right back into smithereens. The air pressure outside is simply too intense to allow that bubble to form. Those molecules are gonna theyll have to go faster than that to exert enough pressure to overcome the pressure, mainly, of the atmosphere, let alone this height right here. So thats what happens. So the water then, since its not cooling, the water goes up to 99. And the water molecules say, hey, lets try it again, gang. They cut out like this. And what happens . Old atmosphere up above says, no, you dont. Smash. Smash them right back down. What happens . No cooling, the water heats up more. Now, the molecules are more energetic, right . Will exert more pressure when they form a bubble, yeah . Now, they form a bubble. Atmospheric pressure up above says, oh, no, you dont. Smash. All the bubble says, oh, yes, we do. Squash. Because, now, the bubbles are pushing out with a muchas much enough pressure to overcome the atmospheric pressure plus the pressure of the water. And thats the temperature in which boiling takes place at sea level. Now, you go up in the mountains where youre closer to the top of the air. Does the atmospheric pressure pushes hard . No. No. So boiling should take place at a higher temperature or lower temperature . Lower. Does it make sense, a lower temperature . Isnt that neat how physics makes sense like this . See . And if you keep taking the pressure away, pressure away, pressure away, youll get boiling at Room Temperature and below. Theres a wonderful, wonderful experiment at the exploratorium in San Francisco. Its my favorite. And all it is, is theres a cylinder, a plexiglass so you can see inside, and a vacuum pump. And you squirt a little water in a little cup. And you put the water in the cup at room water temperature, you can even put your hand in there and everything, and you close the thing. You throw the switch. Stretch it. Take the air out. It starts to lower the pressure. And guess what the little water in the cup starts to do, gang. Boil. Begin with a b. Boil. Boil. And people walking by dont know whats going on, and they see the boiling water. And they ask questions like, gee, how are they heating it up . Theyre not heating it up. But its boiling. The only time you ever see boiling with someone heating it up, honey. But theres boiling when you dont heat it up too. Theres two things that go on with boiling. What are they . The heat you give and the pressure you exert. And if you change either one, youre gonna change the temperature which youre gonna change the temperature of the water. Yeah . And so what happens is its boiling, boiling, boiling. Now, heres a neat thing. It continues to boil. The pressure goes down, down, down. And you continue to watch and, lo and behold, turns to ice. Turns to ice. Its beautiful. The water boils right down the bubbles. You even see the frozen bubbles. And water boils until it becomes ice. So if youre ever with a friend that doesnt believe water is a boiling process, take him to the exploratorium in San Francisco and check that one out. Boiling is a process. Say again. Boiling is a cooling process. Boiling is a cooling process. What did i say . Water is a boiling process. Oh, gosh. Myno. Oh, hewitt, hewitt, hewitt, yeah. Yeah, water is aokay. [laughter] thank you, lee. Thank you. Yeah, but boiling really is a cooling process, gang. And when youre cooking water at home and its boiling away, you just rememberpeople, that, hey, whats the temperature of that water . And they say, a hundred degrees celsius. You turn the flame up. Whats the temperature now . [growls] theyd say 100 degrees celsius. Thats right. Turn it all the way up. [growls] really frothing over. Whats the temperature now . They say 100 degrees celsius. I know something, you know . I know that temperature of water is always the same. And then you say, well, how does it stay the same if i keep turning up the heat . And they say, well, gee, i theres probably no reason for that. Its just a property of boiling water to always stay the same. And you say what . Check your neighbor. It makes sense, gang. Yeah. It makes sense . We get the answer to such thing. Yeah. And it goes, the more heat you put in, the faster it cools and one just offsets the other, and thats what keep the temperature always the same. Really, really nice. Now, what happens if you put a cover on there . Some people say when you put a cover on top of your spaghetti that it will cook faster. True or false . False. True. The answer is true. Because when you put the cover on your spaghetti, you increase the pressure in here a litt