while i'm doing this i'd like to mention a problem that has arisen i didn't plan to drink my coffee right now what i had hoped to do was to drink it and a few minutes so the question is shall i add the cream now or  added later say in about five minutes when i get ready to drink the coffee but we can very easily make an experiment i was this by adding cream to one of them now and 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 and of course there will be a certain amount of cooling and both of these cups of coffee and i 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 it will be a considerable amount of difference in the temperature of those two cups of coffee in five minutes i have difficulty remembering which one cools off the faster but fortunately we have as our guest on zionism an action a scientist who has the minutes one two three four five that's right now let's look at this cup the first thing we did was add cream yes right away that cooled down from this temperature down about in there then it started calling but being you know cooler than the other one is it doesn't give out as world to know if you want your coffee to be hot the end of five minutes are you going to have the cream first or at the end of the time or the thing to do quite obviously from this graph is to put the cream in first and at the end of five minutes you'll have a harder coffee than if you added the cream at the end of that various right just the opposite of what you might think a lot of this after andrew the overall pattern of the transformation of heat well earl all of the various phenomena of heat transfer or keep 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 conduction is a very very slow process that takes place as we will see in our many experiments over a period of time it so here is a model crystal model showing how the atoms look in a solid thing the reason for showing this is that i want you to keep in mind that all substances are made of atoms atoms molecules and it's the rapid state of vibration of the atoms molecules pan of water which we have the do well when you go to heat anything irl you have to bring it into contact or nearby something that hotter and here in the pan of water would bring it up bring a hot flame up from gases burning gases or from a hot plate and the molecules of that hot object hit the molecules of the bottom of the panel set them by burning faster they in turn hit others and this atomic motion is conducted through the metal to the other side where it starts the water 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 that by means of the same atomic motion in through the center where the water is that's right passing on of the atomic motion from molecule to molecule and this next demonstration that you have here is one that is really quite interesting oh 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 some metal some substances are good conductors of heat and others are poor conductors of heat and i say here are six metal rods all the same length all the same diameter but they're made of different metals this person here is copper than aluminum and here's brass and and german silver tin and lead now they're painted with a paint the 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 five minutes and it it is a good conductor cover but look at this and over here lead you see it's change color only this far up showing it's a poor conductor so here we have different kinds of conductors good conductors and and all metals in will have this sort of a characteristic other words it will either be poor or good as  clean there are some semiconductors we might call now about this quirky experiment here that is certainly a very and gene well is another experiment in conduction earl here i'm going to put a few drops of water in this little aluminum to this tube is mounted on the shaft of the motor quite a weapon there the way that cork fucked up 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 in electricity that is an electric field to use for wiring that sort of thing but occasionally we have need of other metals that are conductor of heat but curiously enough even though it's a poor conductor if you make it fit 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 i here's a very interesting little experiment with a piece of paper this ordinary typewriter paper bond paper folded into a little cup now what i'm going to do is for a little water in this paper cup and i hope it doesn't leak and we'll put it over this open flame i don't be alarm scorched at all not a thing there when i suppose that you had a thicker piece of material in the bottom of this would that make any difference no word row i have travel further through the material i anticipated this early so i have another little box with a piece of cardboard in the bottom of a thing that has cardboard in there that you put on top of the paper that size about ten times the thick of that paper and let's see if that helps a little water in it and put it on the over the open flame copper and then hardwood air and the next thing is what a piece of paper around here a favor again copper remember is a good conductor the wood is a four conductor now put the paper around the two and so tight against them and try to burn the paper copper flows quickly into the inside the copper because it's a good conductor but here where it strikes the wood heat flows through the paper hits the wooden stop to can't conduct in a way fast enough paper gets hot and it burns so here's a good conductor for a conductor first water is actually a four conductor of heat and yet the pan of water will be quite quickly due to the second method of heat transfer called convection now convection current is a natural flow of hots water from one place to another here we come back to our diagram of the panda zero 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 full of warmer water rises only water from the side has to come in and take its place like that and again cold water here comes down the side take its place and in turn cool water comes across the top and you see what happened here we have a current or current  convection of current water from the hot region here around continuously and that's why panel heat up quickly well this is the same sort of thing that we have in lakes and various times of the year and also happens in the ocean these convection currents yes the warm water rises and g ocean currents and what would be some practical active application of these various convection currents well in this experiment or oh we're going to set up a convection current of water around this class to the shape of a letter oh this filled with water and we're going to heat one corner here with a flame you know readers right over there are crumbs and then to show that the water is going to flow see it's being warmed here and being warmer to expand and rises you know it will go up the side of the tube in a crossover and see there's quite a convection current there already set up certainly going around there and buildings are heated by a convection water current there in the first basement of the building there may be a furnace to heat the tank of water the water rises through a pipe that flows through the various rooms of the house and back again where it's heated again we have a convection current of hot water and so then we be radiators of course are just extensions of the pipes what they do is to give a larger heating service so that the house or room will heat up much more quickly that's right and of course we have another kind of convection current in the house to around that radiator there's air in this air is warm and as it warms expands and write it up and then the cold air comes in along the floor and we get the same kind of a convection current we had here  this case is the air going around the room so too convection currents are involved in such as this feeding system yes well it's certainly obvious that the hot air heating system is very similar to the hot water heating system in other words these systems are generally down in the basement there's a furnace or sometimes a furnace will be on the main floor but always there is a dock that comes from not from this furnace and it goes in usually at the at the floor line somewhere around the base boortz and then from there the hot air comes in and it's it rises up one side of the room travels across the ceiling and down the other side cross the floor to return to the furnace by another opening in the floor or the  of course it's still open the top and the candle is burning up oxygen and here in the warm nitrogen that's left right as up to two now there goes out well yes of course it is because the oxygen was soon used up to sea and it needed oxygen to keep burning and i will do the experiment again earl and when you put that in there but that tube over there i'm going to put in a little piece of cardboard done here