 Hi, I'm Zor. Welcome to Unisor education. Today I would like to talk again about heat and the temperature. It's kind of related to each other concepts, but there are lots of differences and that's what we're going to talk today about. Now this lecture is part of the course called Physics 14 presented on Unisor.com. Unisor.com is a course which means it has many lectures logically related to each other in logical sequence, in logical order. And all these lectures on the website have their textual equivalent, so you can basically read it like a textbook as well as listening to the lecture. And also the website has lots of problems, exams, etc. The website is completely free. There are no even advertisements, no strings attached at all. And I do recommend you if you found this lecture somewhere else like on YouTube, for instance, I still recommend you to go to Unisor.com and listen to this lecture from the website because it gives you again the text and also there are preceding lectures, following lectures, etc. The website also contains a prerequisite course, which is called Math for Teens. Obviously math is absolutely necessary for physics. So let's talk about heat and temperature. Well, again, we all kind of know intuitively know what these things are, but let's be very precise, more like scientific in this particular case. We know what heat actually is. Heat is a form of energy. So whatever the amount of energy is supplied to a body, it's basically converted into kinetic energy of its molecular movements. Now, what is the temperature? Well, temperature is, as we have already established in the previous lectures, it's an average kinetic energy of the particular molecules of this object. Let me make a comparison. Let's say you have two different cars and you have a certain amount of fuel, the same, we put the same amount of fuel into one and to another, but the cars are different. Now, they start moving and you press the pedal to the metal in both cases, most likely they will go with different speeds. So the speed of the car is like a speed of individual molecules or average speed of the molecules. Amount of fuel is total amount of energy. How you convert the total amount of energy which is supplied to the body into exact kinetic energy of its molecules, well, depends on what exactly this particular object consists of. I mean, different materials behave differently when the same amount of energy is supplied to them. Let's say you have certain amount of heat or energy which is supplied to one gram of water and it increases its temperature by one degree. Now, you have exactly the same amount of heat and you apply it to some other material, not the water, but let's say copper. It will also increase the temperature, so the movement of individual molecules will definitely increase, but will it increase in the same way? I mean, the temperature will be exactly the same. It will increase the temperature of the water by one degree, but will it increase by one degree temperature of the copper? Well, no, actually it's much more. And here is one and it's very important. Every material has its own capacity of converting energy which is supplied to it into kinetic energy of the molecules. And therefore, different materials react differently as far as their temperature is increasing by the same amount of energy supplied, the same amount of heat supplied. And it actually depends on the quality of the material, what this particular object is made of. It doesn't depend on any other quality. So experimentally it was established that certain amount of heat will increase certain amount of material by certain amount of degrees of Celsius. And it depends basically only on the quality of the material. So you have, let's say, one kilogram of material and let's say you want to increase it by one degree Celsius, or Kevin. Let's use Calvin. It certainly requires certain amount of heat to do this, to increase the temperature of one kilogram of material by one degree. And this amount of heat, amount of energy which you should supply to this one kilogram is different for different materials. But for the same material, it actually doesn't depend on anything else. It depends only on the mass and by how much we want to increase the temperature. From 50 to 51 degree or from 20 to 21, it's exactly the same amount of energy. It was established experimentally and for each particular object, for each particular material the object is made of, the amount of energy needed to increase one kilogram by one degree is called a specific heat capacity. So that's very, very important. Every material, and that's not only the solid material, it's also the water and gases, whatever. As long as you know the mass of this object made of this material and you know that you want to increase the temperature by a certain number of degrees, that is sufficient actually to find out how much heat you need for this. Because mass is additive, so if you want two kilograms it will be twice as much heat. And if it's not from 20 to 21 but from 20 to 22, that basically means from 20 to 21 by one degree and from 21 to 22. So again, you double temperature is also kind of an energy thing. So if you have mass of an object and you have certain amount of certain degrees you would like to increase the temperature, if you multiply this by certain constant which is specific for this material you will get amount of energy needed for this particular delta T. How much additional energy you need to supply to this mass to increase by this number of degrees and this is a specific for material. And it's different for different material. And by the way, we already know that one kilogram of water, if you want to increase by one degree of Kelvin, you need 1000 calories, right? Because it's a kilogram, not gram. So gram is one calorie, kilogram is 1000 calories, kilo calorie. And we know that this is equal to 184 J. So this is a specific heat capacity of the water. Now, just as an example, specific heat capacity of, I have certain examples, so this is water. Now copper has specific heat 385 J. So one kilogram of copper to increase the temperature by one degree of Kelvin scale, you need 385 J. By the way, look at this, it's more than 10 times less. So the water requires more energy to increase a kilogram of water by one degree than copper. Now, what else do I have? I have gold, 1000 iron, even less. Still, one kilogram, one kilogram, one kilogram, one degree, one degree, one degree increase. It needs this amount of energy. Now I have uranium, uranium has 116 J. And then I have a hydrogen. Hydrogen has 14304 J heat capacity. So if you see, there is some kind of a dependency. This is the fluid, this is the gas. These are all solids, but this one is heavier. Uranium is much heavier than gold, gold is heavier than copper, right? So it looks like the more dense the matter is, because this is the most dense. The kilogram of uranium takes much less space than the gold, gold has much space than the copper. Obviously copper has much less space than water and water has much less space, one kilogram of water, much less space takes than one kilogram of hydrogen. So as you see, it kind of depends on the density of the material. So the more dense material is, less energy it requires to increase its temperature by certain amount of degrees. Okay, now being as it may, let's examine a little bit further. Now if you look at this only, you can actually graph it. You can have a dependency. Now delta T depends delta E divided by C times M. This is the same thing. So either you express energy or heat, if you wish, as amount, which depends on how much temperature you want to increase. Or given the energy, you can get the degrees, the temperature grows. So amount of energy can be converted into increase of the temperature. The needed increase of temperature requires certain energy. So let's do it graphically. Let's say you have here heat which is supplied and the temperature grows at the temperature. So Q is argument, heat, and T is the function. So I'll use this one. Well, obviously it's a proportional dependency where C times M, specific heat capacity times M is some kind of factor. So you will have something like this graph, right? Now let's talk about melting ice. That's very important. As you know we have different states of matter. Ice, water, gold, and we can basically melt the gold. Hydrogen, we can freeze the hydrogen into liquid hydrogen. So we have different states. So let's see what happens when we are gradually heating, let's say the frozen water, which is ice, into temperature beyond zero Celsius, beyond the melting point. What happens in this case? Okay, so in the beginning we have ice. This is ice. This is zero temperature of Celsius. Okay, so as ice being gradually heated, we have this proportional kind of dependency of the increase of the temperature as the function of amount of heat supplied. What happens around zero Celsius? Well, the ice begins melting. Here is a very interesting thing. Ice has capacity, specific heat capacity, 20, 90. And water, as we know, has 4184. That's very interesting. It means that to increase the temperature by one degree, if it's an ice, if it's a one kilogram of ice, you need 20, 90 J of energy. But if it's water, it needs significantly more, like twice as much. So what happens when we are reaching the point of zero, the point of melting? Well, ice begins melting, but it doesn't really melt immediately. It gradually melts. Now, as we supply heat to the melting ice, well, there is certain water and certain amount of ice, right? So the water actually is mixed with ice. And we do supply certain amount of heat to this mix of ice and water. But what happens? Well, water touches the ice. Ice cools the water. Water heats the ice. So the melting continues, but unless it's complete, the temperature will still be the temperature of the ice and melting ice and half frozen water, which is around zero. So what I mean is, as we are increasing the amount of heat, which we are basically supplying, our temperature remains the same. Up until the point, so this is melting point. Up until the point, when everything is melted, the complete ice is melting, then we have a different coefficient between amount of heat and growth of the temperature. We need actually a little bit more heat to get to the same difference. So this is water. So this is below, temperature is below zero, when everything is ice. Now at zero, so we are increasing the heat proportionately, let's say to time or something like this, and our temperature of the ice grows. But when it starts melting, we are still increasing amount of heat, which are supplying into this mix of ice and water. But the temperature of the mix remains the same until it's completely melted. And then it continues growth, but at a different coefficient. So this coefficient relates to this specific heat. And this coefficient relates to this specific heat. So it's different proportion. Mass is the same, one kilogram, one kilogram. But the coefficient is different. That's why we have, this is a little bit steeper than this one. So this is a very interesting observation. That change of state from, let's say, solid to liquid, or the same thing from liquid to gas, requires certain amount of additional energy just to convert the state from solid to liquid. So state conversion or state transformation rather probably would be a better word. State transformation requires additional energy. And not a small amount of energy, by the way. In the case of ice melting into water, one kilogram of melting requires three, three, three thousand joules. You see, to increase by one degree the temperature of the ice, you need two thousand something joules. But to convert one kilogram from ice to melt it, when it's already reached zero temperature, just to melt it requires so much energy. So change of state is a very important and very heat consuming process. The melting in this particular case. Now, I have to tell that there is a reverse, let's say you're freezing the water into ice. Now for this, you need to extract the heat from the water. You have to cool it down. So you need something like a refrigeration or whatever, which takes the energy from the water and somehow converts it or disposes it into some kind of condenser or whatever it is, how refrigerators are made. So again, to keep something, to freeze something, you need to extract certain amount of heat, which is exactly equal to amount of heat you need to supply to make a different, to make a reverse transformation. So you need certain amount of heat to supply to ice to convert into water and you need to extract exactly the same amount of heat to convert water into ice. So this is a very important concept of how the heat and temperature are related. As long as we don't change the state, as long as the state is not transformed, if it's a solid, it's a solid, then you have basically a proportional dependency between amount of heat and the temperature. You increase the amount of heat and the temperature is proportionally growing. And this is basically... As soon as you reach the point of state transformation, then you will have this horizontal line which indicates that you are supplying the heat in this case and the melting is basically going on, the transformation of the state is going on. And it requires a lot of energy, actually. Let's just think about... If you increase the temperature of ice, let's say, from minus 50, let's say, to zero, you need 50 times this, which is about, what, 100,000, right? 50 times 2,000, that's about 100,000. Then after you have reached the temperature of zero from minus 50, which is a lot of Celsius, to zero, that's 50 degrees, you have to spend about 100,000 joules. Then to melt this kilogram of ice, you need three times as much. And then you have to increase the temperature, let's say, again to 50 degrees of... Plus 50 degrees Celsius. That requires 50 times 4,000, more than 200, still less than to melt. So melting is a very energy-consuming process. So that's how you have to really understand. It's very, very important. The range of state is really very much energy-consuming process. And there are just two words which I just wanted to say. I usually... I don't think you will ever use these words, but there is a scientific terminology. This process of melting requires additional energy. So the process of melting, therefore, is called endothermic, which means it's consuming energy. If the reverse process, let's say we are freezing the water, so the energy flows from the water outside, refrigerator, whatever, it's called exothermic. So endothermic is the process which consumes energy. Exothermic process is the one when energy is flowing outside. Well, that's basically it. That's all I wanted to talk about the dependency between heat and temperature today. I do recommend you to read the text information for this lecture on unison.com. You have to go to the chapter called Energy, and then there is a sub-chapter Heat and Temperature paragraph. Okay, that's it for today. Thank you very much and good luck.