Science in Action: The Flow of Heat (ca. 1956)

science in action science in action is produced by the West's oldest scientific institution the California Academy of Sciences now in its 100th year thank you may I pour you a cup of coffee while I'm doing this I'd like to mention a problem that has arisen now I didn't plan to drink my coffee right now what I had hoped to do was to drink it u in a few minutes so the question is shall I add the cream now or shall I add it later say in about 5 minutes when I get ready to drink the coffee but we can very easily make an experiment out of this by adding cream to one of them now and uh then later when we get ready to drink the coffee we can test that against the other cup of coffee to which we will add cream at that time now of course there will be a certain certain amount of cooling in both of these cups of coffee and that cooling will be due to the flow of heat flow of heat from the coffee to the cup and from the coffee to the air now there will be a considerable amount of difference in the temperature of those two cups of coffee in 5 minutes I have difficulty in Remembering which one cools off the faster but fortunately we have as our guest on science of action a scientist who has the answers to all such problems I'd like to have you meet him he's an old friend of our program professor physics at the University of California Dr Harvey E White how are you there Harvey good evening Earl say can you help us with this coffee I'm not sure about all the answers Earl but we'll try on this one fine uh here's a little diagram made up of two cups of coffee this one hasn't had the cream added it's black yet this is the one to which cream has been added now this cup here that is black started at the same temperature this one did but being hotter it cools off more rapidly and we can show that a little graph here oh this represents the first the cup of coffee that's black it cools off with time so that in about 5 minutes 4 and 1/2 5 minutes it's gone down almost to room temperature but not quite this would be the time scale here in minutes 1 2 3 4 5 that's right now let's look at this cup the first thing we did was add cream yes right away that cooled it down from this temperature down to about there then it started cooling but being now cooler than the other one was it doesn't give out as much heat per minute and it follows a curve that looks similar but always stays below the other one goes along like this oh yes but now don't forget we haven't added the cream to this one yet oh yes the first one so now if we add the cream here at this point it cools down below the other and it goes on oh so now if you want your coffee to be hot at the end of 5 minutes are you going to add the cream first or at the end of the time well the thing to do quite obviously from this graft is to put the cream in first and at the end of 5 minutes you'll have the hotter coffee than if you added the cream at the end of that period that's right just the opposite from what you might think well now how does all this enter into the overall pattern of the trans of heat well Earl all of the various phenomena of heat transfer or heat traveling from one place to another can be classified under one of three classes of heat transfer we call them the first one is conduction the second one is convection and the third one is radiation now conduction is a very very slow process that takes place as we'll see in our many experiments over a period of time it takes quite a while to conduct heat convection however is a more rapid process mhm but radiation is still more rapid as we'll see later on well suppose we go back to that first one in conduction and looked at these various demonstrations that Bob Bell was set up here well here is a model a crystal model uh showing how the atoms would look in a solid the thing the reason for showing this is that I want you to keep in mind that all substances are made of atoms atoms and molecules and it's the rapid state of vibration of the atoms and molecules that constitute heat if you add heat to a solid any solid the atoms and molecules vibrate faster if you allow it to cool off the atoms and molecules slow down so that heat or temperature is a measure of how fast they're vibrating well how would that affect this pan of water under which we have the heat well when you go to heat anything Earl you have to bring it into contact or nearby something that's hotter and here in this pan of water uh we bring it up bring a hot flame up from gas burning gases or from a hot plate and the molecules of that hot object hit the molecules of the bottom of the pan and set them vibrating faster they in turn hit others and this Atomic motion is conducted through the metal to the other side where it starts heats the water up now then on our chart that we have here we would have the flame at this point and then we would have the flame transferring the heat to the bottom of the container and then from that by means of this same atomic motion into the center where the water is that's right it's passing on of the atomic motion from molecule to molecule this next demonstration that you have here is one that uh it's really uh quite interesting now let's see first of all you have a heat container here and you have a certain amount of steam that's passing over through here and down here and then what are these various rods well this is to show Earl that some metals some substances are good conductors of heat and others are poor conductors of heat I see here are six metal rods all the same length all the same diameter but they're made of different Metals this first one here is copper then aluminum and here's uh brass and and German silver tin and lead now they're painted with a paint that changes color when they get hot although they're all heated to the same temperature down here at the bottom you see this one has changed color all the way up already it's been going about 5 minutes and it it is a good conductor cuffer but look at this one over here lead you see it's changed color only this far up showing it's a poor conductor so here we have different kinds of conductors good conductors poor conductors and All Metals then will have this sort of a characteristic other words they will either be poor or good as far as well some in between there are some semiconductors we might call them about this cork experiment here that is certainly a very ingenious well this is another experiment in conduction Earl here I'm going to put a few drops of water in this little aluminum tube this tube is mounted on the shaft of a motor and I'm going to put a cork in the end of the tube now and stop stop it up good and tight and now I'll put this wooden clamp around this shaft and I'll turn the motor on now what'll happen is the friction will develop heat it will be conducted through to the tube to the water and caus it to boil and then I hope steam will develop and blow the little cork out there she goes here it was the conduction of the heat through the metal to the water that caused it to boil well that's really quite a weapon there the way that cord popped out of course all of us know about the advantages of metals that are conductors such as copper and some of these others we've seen demonstrated copper and electricity uh that is an electric field used for wiring that sort of thing but occasionally we have need of other metals that are non-conductors such things used in insulation in glass wool uh lead shields for X-ray equipment uh oh wood and various other things but uh how about paper now what sort of conductor is that Harvey well paper Earl is a very very poor conductor of heat but curiously enough even though it's a poor conductor if you make it thin enough and distribute the heat over a large enough area you can conduct a lot of heat through a thing like a thin piece of paper now here's a very interesting little experiment with a piece of paper this is ordinary typewriter Paper Bond paper folded into a little cup now what I'm going to do is pour a little water in this paper cup and I hope it doesn't leak and we'll put it over this Open Flame now don't be alarmed or all now there's a let's see there should be a Scorch Mark there if anything's going to happen I don't see anything at all well this paper can't possibly burn as long as that water is in there the water is starting to boil can we dump the water back in and see what the underside of that looks like yes let's try that see the paper is not scorched at all not a thing there well now suppose that you you had a thicker uh piece of material uh in the bottom of this uh would that make any difference in other words the heat would have to travel further through the material I anticipated this Earl and so I have another little box with a piece of cardboard in the bottom of it see well that has cardboard in there that you put on top of the paper that's right it's about 10 times as thick as that paper now let's see if that helps us any put a little water in it and put it on the over the Open Flame are you hoping it'll burn Earl I'm just looking down here to see what well I see Scorch Mark appearing there it's water out there there's a Scorch Mark already in other words then the the thinner the paper is the more difficult it is for it to burn because the heat will be transferred through and yet the heavier paper here the heat wasn't able to go through as rily that's right let's put this back on here and let it go a while see if we can get the water to boil in other words we come back to that later in the program we'll find that the water is still boiling and the paper will not be touched that's a good idea mhm fine well now this uh this Rod that you have have here is another quite interesting one let's see first of all a piece of metal here this is copper copper and then hardwood here and the next thing is what a piece of paper around there piece of paper again copper remember is a good conductor the wood is a poor conductor I'll put the paper around the two and hold it tight against them and try to burn the paper oh yes we have a we have a Scorch Mark there let's take the paper up and we see what happens The Scorch mark corresponds with the wooden area but there's no burn mark on the copper part now that again is conduction right that's right the heat flowing through the paper hits the copper flows quickly into the inside of the copper because it's a good conductor but here where it strikes the wood the heat flows through the paper hits the wood and stops it can't conduct it away fast enough paper gets hot and it burns so here's a good conductor poor conductor with a piece of paper around it this water we've all seen uh how water can be heated it's a poor conductor and yet it quite often Heats quickly over an open and hot fire uh we see it happen but just how does it happen and why does it happen well of course water is actually a poor conductor of heat and yet the pan of water will heat quite quickly due to the second method of heat transfer called convection now a convection current is an actual flow of hot water from one place to another here we come back to our diagram of the pan you the Earl when the heat is conducted through the bottom of the pan it heats up the water here in this area and the hot water has expanded and it being lighter now Rises to the top it goes up here toward the top of the pan well if warm a water rises cold water from the side has to come in and take its place like that and again cold water here comes down the sides to take its place and in turn cold water comes across the top now you see what happens here we have a current oh current is set up there a convection of current of water from the hot region here around continuously and that's why a panel heat up up quickly well this is the same sort of thing that we have in Lakes uh various times of the year and also happens in the ocean these convection currents yes the warm water rises and gives us these ocean currents well now what would be some practical application of these various convection currents well in this experimenter we're going to set up a convection current of water around this glass tube in the shape of a letter O this is filled with water and we're going to heat one corner here with a flame we move this right over there there it comes and then to show that the water is going to flow you see it's being warmed here and being warmer it expands and Rises yes it'll go up the side of the tube and across over and down and we'll get a convection current clockwise around this L and this D that you have then would indicate that that's right in order for you to see that the water is moving I'll put this Dy in the top see there's quite a convection current there already set up certainly going around there you see that all right in other words a poor conductor such as water can be rapidly heated due to this convection current which is set up yes now there's there are practical values to which this can be put Earl many houses and uh uh buildings are heated by a convection water current they're in the basement of the building there may be a furnace that heats a tank of water the water rises through a pipe and flows through the various rooms of the house house and back again where it's heated again we have a convection current of hot water incidentally the radiators of course are the just extensions of the pipes what they do is to give a larger heating surface so that the house or the room will heat up much more quickly that's right and of course we have another kind of convection current in the house too around that radiator there's air and this air is warmed and as it warmed it expands and it rises then the cold air comes in along the floor and we get the same kind of a convection current we had here only in this case it's the air going around the room mhm so two convection currents are involved in such a heating system yes well it's certainly obvious that the hot air heating system is very similar to the hot water uh heating system in other words these uh systems in houses generally down in the basement there is a furnace or sometimes the furnace will be on the main floor but always there is a duct that comes from that furnace furnace and it goes in usually at the at the floor line somewhere around the baseboard and then from there the uh hot air comes in and uh it rises up one side of the room travels across the ceiling down the other side across the floor to return to the furnace by another opening in the floor or the baseboard now here's another experiment convection Earl will you hold that glass cylinder I certainly will I'm going to light a candle here at the bottom of this box and then I want you to place the glass tube over the top of it and press it down on on that cork so that no air can get in at the bottom of course it's still open at top and the candle is burning up oxygen in here and the warm nitrogen that's left Rises up the tube oh that goes out well yes of course because the oxygen was soon used up you see and it uh needed oxygen to keep burning now we'll do the experiment again Earl and when you put that in there put that tube over there I'm going to put in a a little piece of cardboard down in here slip this down in here and dividing the cylinder into two parts but now the CL the flame will burn on as long as you leave that cardboard in because what has happened is that the warm air started up and it started up one side first and that started a convection current up here and cold air came down the other side well how do you know that it goes down this side and up this side well I don't Earl but if I put my finger over there and try both sides it gets warm here so I know the warm air is coming up this side now and the cold air is going down there well to test that if we take this out by then very very soon the flame should die down again because the oxygen again will be uh tight at the bottom oh there it goes I get this back in I may be able to get it back again there they oh there she comes in other words we set up a convection current again so that we reestablished the same thing as before well let's go back over here and look at this uh boiling water that we have here in the paper cup and see what's happening oh she's still boiling merrily away can we dump that into the see if I can keep from burning myself here turn side down and on the bottom hardly any indication that the uh piece of paper just plain typewriting paper has been in this flame all this pretty time yeah certainly very striking well now Earl we come to the third method of heat transfer many you've gotten up sometimes in the morning and seen the sun come up over the horizon on a clear morning and just as soon as you see the light you feel the heat from the Sun so this shows that from the sun he has traveled with the same speed of light and that's 186,000 m a second so when I said radiation is fast I meant fast it travels with this enormous speed now this that you have over here then is a heat uh measuring device yes this is a thermal pile Earl there's a little metal horn or reflector and in the back of this horn is are a lot of little wires and these wires are arranged so that when heat falls on them they develop an electric current tiny electric current and that current through these wires goes to a meter here which we project on this screen oh yes and you see the pointer of this meter here it moves when I turn this horn it's a detector of heat now if I point it at the floor you see it shows in the center reading a reading of zero yes now if I point it towards your face see the needle go over the right is that my face is doing that well that's because your face is warmer than the than the floor now if I pointed at the wall back here it goes back toward zero again point at my face it goes up back at the floor now in my hand it goes up again anything anything that's warm is indicated by the movement of the pointer well that's certainly a very accurate uh method of measuring heat uh coming back to something that we've known for many years u a heating device radiant heat the oldfashioned fireplace of course down at the bottom here is the uh where the fire would be and then we have a chimney that comes up here the important thing about the fireplace is again convection currents most of the heat comes up here and by radiant heat or reflected heat we get the heat coming out in the room by means of such things as fire brecks in the back of the fireplace that's right earol and of course the radiant heat is what heats up the room all of the convection currents are up the chimney and that's fortunate because in that warm air there's a lot of carbon monoxide with poisonous gases and it's a good thing they do go out the chimney when You Face a fireplace and the Fire Burning Brightly you'll feel it on your face and if you turn your back to it you'll see that the heat is cut off from your face so we get there an indication that the radiant heat are light waves traveling and when they hit your face they're absorbed or hit your body and changed into heat so what we have then in our fireplace at home is very much the same sort of thing that we saw demonstrated in this experiment a little bit before in other words convection currents going up the tube and without the convection currents of course you wouldn't be able to have a fire in the fireplace anymore than this flame would be able to stay there for just a slight second now there's one other type of heating that we haven't mentioned yet and that's panel heating it's a newer thing that's just come in and according to Engineers it's very very satisfying Factory and economical now just how does this work Harvey well in panel heating Earl you have a similar principle to the fireplace you have a large area that's warm like the brick walls only here you warm the floors or the ceiling or sometimes the Walls by by hot water in pipes this warms up the whole floor area ceiling area and the warmer areas radiate heat toward the people the occupants of the room if you even though the room may be quite cold this radiant heat when it hits your face hits your body it's absorbed and becomes heat and you feel quite comfortable well this final experiment that you have over here this gear that you have is is certainly very interesting those big reflectors just what is all of this gear now can you give us an idea as to how this works Harvey well Earl here we have a large metal reflector the kind you have in a search light and uh at the focus of this search light mirror we have one of these thermal piles now way over across the room way down the other end of the laboratory about 30 or 40 ft down there isn't it yes you'll find another mirror down there is just like the one we have here and Bob Bell has a candle flame ready to put in this mirror now when he puts the candle flame at the center focus of this mirror it acts like a search light it reflects the heat Rays as well as the light and we have a beam of heat rays and light coming across to this one here they're again reflected and come into the thermop pile Oh now we'll see it on the galvanometer there and we'll see it on the little pointer of the galvanometer as it moves now Bob if you put the candle flame in will'll watch the pointer does it move over Earl there it goes over that shows it's receiving heat here now will you take the candle flame away Bob did it come back again coming back once more can we do that another time over it goes now take the candle out Bob see the pointer come back again well uh just how far could you separate these reflectors now and still get that sort of a reaction on this meter well Earl we could put that candle flame 100 ft a mile 2 miles 5 mil even 50 mil away if it was a clear day and we could pick up the heat from it and bring it over here and receive it as a matter of fact uh astronomers uh use thermop piles to detect the heat radiation from Stars Believe It or Not millions of miles away and then then they mount equipment something like this in their telescopes and are then able to get a to get a reading yes they reflect the light or through their refractor bring the light to a focus from a star on a little thermal pile and record the current from it and measure their heat radiated by a star millions of miles away well this is certainly one of the most accurate pieces of measuring equipment that I've ever seen and looking back over these demonstrations that you brought to the laboratory it seems to me that it boils down again to these three basic issues first of all conduction secondly convection and third radiation and no matter where we turn in our everyday lives we're going to come up against these factors that have to do with heat that's right well um I want to thank you again for coming to science in action to bring these wonderful experiments and I see your assistant Bob Bell is still wrestling with the Mir down there thanks also to Bob for helping with these demonstrations it's been a pleasure Earl I'll be back in just a moment with the animal to eat this is the skull of our animal the week and as you can see from those large teeth it's a rodent a burrowing rodent and directly underneath it is the size of the new new born youngster very very small just about the size of the skull of the adult youve probably guessed what our special pet is that we have here in the laboratory it's a pet California gopher this one happens to be the special friend of Bill mball now bill you have a carrot there would you see if you can put it down in here and what do you call him what's his name dig dig oh fine put it over here and let's see if he'll uh if he's interested in it this is unquestionably one of the Tous Gophers that I have ever had an opportunity to see he's not quite sure whether he likes that or not does he he's pushing it over in the corner there how long have you had him as a pet now well about a year about a year you want to put some of this down here over in the side and see what happens uh very easily now he's out yeah there he goes see if he's interested in that oatmeal I know sometimes he fills these pouches with that of course Gophers don't see very well they do he hear however extremely well so that if you happen to come upon one that's working in your front lawn if you uh don't step very carefully he'll know that you're there although he may not be able to see you notice this very short tail now that's quite important as the Gopher he doesn't he's a little bit uh doesn't want me to demonstrate that tail but notice how short it is that's again quite important to the Gopher because it enables him to run backwards in the Burl he's washing himself there now oh you cute little rascal you you know gophers make wonderful pets although when we find them in our lawn why we usually want to get rid of them now not all Gophers have the appearance of this well I'd like to show you some other color patterns these are steady skins this is a Milano this is a desert form here you can see the difference and here's an albino now in the eastern United States they have a gopher that is somewhat different from our Western one uh here are the two types and main difference is in the size of the front feet notice the size of this big foot this is the Eastern gopher the smaller size of the uh the foot of the western gopher principal differences between the eastern and the Western Gophers so let's see what our fellow dig is doing here again seems to be quite interested in this how often do you feed him Bill about twice a week or so twice a week well he's really a good patent and this is his normal cage that you keep him in I hope you'll keep us advised as to how dick does in the future and thanks very much for bringing him to science and action now here's a type of equipment that we have have an opportunity to examine a little bit more closely on our next program when we look at our radar defense system our special guest on the program that time will be Brigadier General Andrew of the US Air Force we hope you will plan to be with us then thanks a lot you have just seen another in the fascinating television series science in action science in action is produced by the California Academy of Sciences under the supervision of Dr Robert C Miller [Music] e