Let's continue to talk about the different form of heat transfer. Let's go first to conduction. Conduction, usually we are talking about thermal energy is being transferred from one molecule to another molecule, from one place to another place. Through the direct contact between these two particle or molecule so that heat energy can be transferred from one to the other as kinetic energy. So in this particular diagram very easily you can recognize that we have a lot of particles lining up in this particular plane. What we have is if we heat it up what we have is the heat is coming up into this single molecule. And when it's being heated up, it starts to vibrate. It increases kinetic energy. And that kinetic energy is being transferred to the next molecule and make the next molecule vibrating faster. As a result the energy transfer from one particle to other particle and gradually they spread over an entire surface or entire volume. In that process, we call it heat transfer. Again using the equation that we talk about, it is very easy to understand what we are really talking about. We are talking about the transfer of energy per unit time. Q divided by t. It is affected by the property of the substance. K. In this case, K is referred to the conductance of this particular substance. And its affected by the area, the difference in temperature as well as the distance between the heating surface and the food or the target subject. Now so in this case. Q divided by t refers to how fast this particular substance can be cooked. K as I said conductance. A very specific characteristic of this food. For example steak, pork or chicken. A refers to how large is the area. This heating surface is in contact with the food. t is how hot is the surface clear above the food.

How large is the difference between the two. And of course, how fast the heat can be transferred depending how far they are away from each other. The shorter they are close to each other or the thickness of this particularsteak is thinner than we will say that the heat can be transferred faster through the steak. Now so that's how we understand how heat is transferred. Now for the principle of this conduction, we need to recognize that in fact food heats up always very slowly because there is a lot of cell structure in food. Which they requires the heat energy to make them into movement into kinetic energy. And so therefore this thickness the shape of the food the area of contact the temperature difference between the pan and the food as well as how much time it takes all comes into play. And if you remember that particular equation you understand. How you can manipulate the system so that you can cook the food more effectively. Now there's another element I want you focus on which is, how much energy is required to heat up the food. And that's another element that you need to remember. In this case Q is the same thing, talking about amount of energy. But then there are now two other elements that we need to focus on. One is delta T. Delta T refers to difference of temperature and m and c. m means that actually how large is that particular piece of food you want to cook it up, of course. The larger it is you need more energy, the smaller it is you don't need as much energy. And the other part which is about the heat capacity of a specific heat capacity. Again another very specific characteristic of a substance or material. And some of the substance they need to take a lot of heat energy in order to raise the temperature, some of them don't. We need to understand for most of the food in fact we are having them cooked in water. And water in general actually has a very high heat capacity.

So what I mean is that in order to raise the temperature of this particular substance which is mostly made of water, you need to use a lot of energy. Of course, there are other substances such as metal, they don't need to use a lot of energy. You can raise the temperature very easily. So what is it that I want to show you that about the relation between conductance and heat capacity. Essentially we will say that some substance, they have very high conductance. They conduct the heat very fast. Some very slow. And on the other hand, on heat capacity some of the material, they need to take a lot of energy in order to raise the temperature. Some don't. And we plot them all into one single graph. For example, if you look at the y axis, it is referring to conductance. You may see that in fact some of the metals such as silver and copper, which we use for making a cooking utensil, pot or so. They are usually made of metal and they have a very high conductance. What I mean is that when heat go through them they can be transferred very quickly through them. On the other hand if you talk about water, meat, fish these are mostly made of water as the major content, the conductance is very low. So what I mean is if you want to heat up water it takes a much longer time compared with the time you take to heat up the same metal. On the other hand if you look at the x axis. We're talking about the heat capacity. Water has a very high heat capacity. Meaning that you need to use a lot of energy in order to raise it's temperature. So combine together what it mean is that you can use very little energy and very quickly. You can heat up metal. While on the other hand for most of the food made of water, it takes a lot of energy. And it takes a long time for you to allow the heat to transfer into them and heat them up.

With that in fact it has lot of implications how we cook things. For example we do stone grill. Why do we want to use stone grill? Because stone in fact they can store a lot of the energy. So that they can gradually transmit out and be passed on to the meat. If you want it to be even faster what you do is you can do the tepanyaki. Which is using a stainless steel as a surface which allows very quick heat transfer. Similarly probably you have encounter burning of your tongue when you're trying to eat pizza. Think about that, what happened in a pizza. You'll find that on the pizza on the surface that may be tomato that may be cheese or so. These are watery substance. In a way they have very high heat capacity. So they store a lot of heat in them so when your tongue get in contact with them. You have all this heat stored in them they will be passed on to you very quickly and therefore you get burned. On the other hand if you look at a lot of the air bubbles and all this, they have very low heat capacity. So when you're biting onto the crust, where because there's lot of air bubble in it, in fact you don't get burned very easily. In order to illustrate this relationship of heat conductance and heat capacity. We are going to go to some experiments to show you how it can be illustrated.