Properties of a System

Okay, welcome everybody. So, in this particular segment, it will be pretty focused segment, but I'm going to talk about properties. Actually, the word property is something that we use in day-to-day language, so it should resonate with you fairly easily. But these properties, what I mean by that is this is the characteristics of a system because we define what the system is. Now, I talk about the property because, as you will see soon, we'll have a state postulate, and all I need to define is what a property is. And, you know, I'll give you a couple of examples to go by, like temperature, like pressure, like density. I abbreviate density with rho, Greek letter rho. Okay, but before going forward, let me divide the properties into two, and I take the liberty, and I wrote them already here to make it a little faster than usual. But this intensive property itself means that these are the properties that are independent of mass. Okay, so this particular property is independent of mass. The extensive property, it's not going to come as a surprise to you, but now it will depend on mass, depend on mass. Okay, and the best way to differentiate, you know, whether something is a property and function of mass or not is to kind of look at it this way. Okay, all right. In this, I want to give an example here. As you see, let's say that this is an oil tanker carrying a lot of oil, right? There will be some pressure, and there will be some volume of it, right, associated with the particular tanker. But then, in reality, what they do is they don't have like one huge compartment of all the oil in a tank. If one section is damaged in here, what will happen? That this, the whole ship will go down, right? So, what they do is they make it into many many different compartments, and they're isolated from another. So, what happens is if one leaks, you know, it's going to be fine, then, you know, for nature purposes as well, right? But the question now I have for you is, when I make this into compartments, as shown over here, I give an example too obviously, what will happen to the pressure? Well, the pressure is going to... Let's say that I have two of them. Am I going to divide the pressure by half? Like, if it was 100 kilopascal, is it going to be now 50? No, not really. What will happen is now it will stay exactly where is that. Pressure will be pressure, right? But obviously, I divided the volume by two. That was the whole point of doing this, right, for protection purposes and nature conservation purposes. The volume by two. So, okay, now let's look at these definitions and where these two fit. Okay, so you can see pressure. Because the mass is half of it here, right? Pressure is the same though. So, okay, then this seems like independent of mass. How about the temperature? When you divide something into two, like the example that I gave, will go temperature by... Let's say I have 10 compartments, is it going to be temperature by 10? No, not really, it's going to stay the same. How about the density? Is the density of oil going to change over, you know, how many compartments I have over there? No, not really. So, you can see in here, these are all intensive properties. Okay, and I gave the example to you in terms of the extensive property, volume is one of them. Well, it goes without saying, mass depends on mass, right? So, it is also something. And I also have, like, total energy. We'll use these definitions to enter a total energy is capital E, and I can have a kinetic energy, I can have a potential energy, I have internal energy. Again, I don't want to, you know, give you a lot of lingo, and especially the internal one, you might not be familiar with. We'll cover those. Okay, one thing is that this upper that I'm going to use, this internal energy capital. So, the capital letters will indicate it is an extensive property. Okay, something to note. Okay, so there is another definition that I want to go over related to the property. It's called the specific property. Okay, and it is an extensive property which depends on mass, and when you divide that by mass, you're looking at a per unit mass basis. Okay, and I gave the example of this, you know, energy, total energy. So, basically, what I gave as an example is E, capital E, divided by m, and we're going to call this lowercase e. Typically, specific properties are expressed in terms of lowercase letters, but I'm going to write this in here. So, this is going to be kinetic energy per unit mass, 1 over 2 m V square, right? Kinetic energy. So, this is the kinetic energy per unit mass, right? Plus potential energy, mgz. So, divide by potential energy, so it's going to be potential energy per unit mass. As you know, it's mgz, so it's going to be g times z, and m dropped out. And the internal energy, we'll talk about it, but lowercase u. So, I'm getting ahead of myself, but we are going to use these kinds of things a lot. So, I want to just drop it in there just to get us used to it. I'm not expecting you to understand fully at this point in time. Okay, okay, one other thing. Oh boy, we are going to use it so often, and we are going to use this actually more often than volume. And I'll actually go back and look at this, the way that I define volume. Maybe you have noticed that. Did you notice that I put a volume and I put a bar in the middle of it? Why do you think they do? I mean, just for the hobby, you know, I do that you think? No, not really. I don't do that, you know. This is not my hobby, right? So, I do this, volume divided by mass. Okay, and then what I get is, well, still specific volume, right? I cannot call it s because it is common to mess many different things specific, right? So, I have to call it specific volume, but the specific volume will be abbreviated by the letter v or lowercase v. So, here's what the problem with the v letter is. The capital letter V and the lowercase v looks very similar in your exams, and you do get confused. Okay, so in order to address the issue with that, I put a bar in a capital V so I can differentiate volume and specific volume. Because, as I said, this specific volume will be used very, very often. Or, some people call this V bar. Up to you, I don't really have a preference. You do what you gotta do. But I do it this way, you know, like a v, but it's almost like, you know, much harder to see that it is a v. Okay, just I want to be double or triple sure that I'm not making a mistake here. Okay, let's look at the density. The density actually is something that we know for a little while now, right? Mass divided by volume. Let me immediately ask you a question. What happens when I multiply specific volume by density? Ah, did you see that? I get one, right? Like mass mass, volume volume, so I get one. So, basically, this density is the reverse of specific volume, right? So, I want to just write that down for us for our purposes. So, the density will be one over specific volume. Okay, let's talk about another one called specific gravity. As, you know, looking at the definition over here, you can see that it's going to be gravity by mass. Wrong. That's not going to be it. Unfortunately, this definition of specific fails over here. Actually, the way that we define this is, this is the density of what I'm dealing with with respect to the density of water at 4 degree C. Okay, there's, you know, some things that we need to discuss here. Why am I doing this? First of all, I mean, I had a density, you know, so why am I dividing a density by a density? Well, I'm normalizing it, number one. And I'll give you another... Well, what's the unit? What's the unit of specific gravity? It is unitless, right? So, that's going to help me. Whether I'm working with British gravitational or I'm working with the SI units, I'll still get the same, you know, number. Okay, um, the second question I have for you is, what is so special about 4 degree C, right? Why not zero, right? Or 32 Fahrenheit? So, well, this is what it is. Water is most dense at 4 degree C, not at zero. I want to highlight that this is 1000 kilogram per meter cube. This comes in actually quite handy when I'm dealing with, let's say, mercury. Okay, we don't use this as often as we used to, but, you know, mercury. So, that's going to be... The density of mercury is 13,600 kilogram per meter cube. Okay, divide this by 1000 kilogram per meter cube. You get to see that this is 13.6. Okay, okay, good. So, here's the deal. I don't want to use this. I want to use this. This looks much more, you know, user-friendly. So, that's kind of like the motivation behind using this. But as long as what you're doing, it doesn't really matter. It's simply multiplied by a thousand. That's what you're going to get if you're using SI, right? So, there are other ones that sometimes we cover, such as specific weight. But I don't really use it a lot in thermodynamics. I use it very often in the fluid mechanics, but then I introduced it over... Just no need. Okay, so this is what you need from this section. Thank you for watching this.