 Hello, welcome to my channel. My name is Adrian and today in understanding thermodynamics, we are going to look at the properties volume, mass, density and specific volume. Now for the contents of this video, we will consider the properties volume and mass. We will explain how density and specific volume are calculated and we will explain why density and specific volume are intensive variables. Now, volume is often used to denote a quantity of substances and that easily fill a container such as gases or liquids. For instance, we can measure the amount of a soft drink by the volume in liters or in milliliters. So you'll often find in the stores, you can buy a two liter Coke, two liters denoting the volume or the amount of Coke that you're going to buy. It is clear that the volume of a substance is dependent on the quantity of that substance. A drop of water and a cup of water cannot have the same volume. Therefore we say that volume is an extensive property. Now in engineering, we work with large volumes and it is sometimes more convenient to measure volume in cubic meters rather than using liters. Now for rectangular objects, the volume is the length multiplied by the breadth multiplied by the width. The volume of the box in this picture is therefore 0.6 meters multiplied by 0.45 meters multiplied by 0.4 meters and that will give you a total of 0.11 cubic meters. Now because we know that there's 1,000 liters inside a cubic meter, we can then say that 0.11 cubic meters is 110 liters. Now for irregularly shaped objects, we often use mass to denote quantity compared to using volume. Now imagine if you go to the shops to buy some meat and you can see in the picture here, the meat has a very irregular shape. So we'd rather go and say, oh I want 200 grams of lamb meat or a 500 gram steak piece rather than oh I would like 200 milliliters of chicken please. So in engineering, we use kilogram as a unit of mass. Now the mass again is dependent on the quantity of the substance. Therefore mass is also an extensive variable. Yeah, talking of all this meat is making me hungry. After this video, let's put some meat on the fire. What do you think? Next let's look at density. Now we said that substances have properties and we can use to identify and describe them and density is one of these properties. Density can be calculated by taking the objects mass and divide it by its volume. Now we know that the density of a rock is much higher than the density of air in a balloon. So let's consider this block of cheese on the scale. Its dimensions is 12 and a half centimeters by three centimeters by 8.5 centimeters. This gives it a volume of 319 cubic centimeters. The mass of the cheese is 440 grams or 0.44 kilograms. The density of the cheese can be calculated from mass divided by volume and we get a value of 1,380 kilograms per cubic meter. Now water's density is approximately 1,000 kilograms per cubic meter. In fact, the exact value is 997 kilograms per cubic meter at 25 degrees Celsius and air's density is 1.18 kilograms per cubic meter. But this also varied depending on temperature and pressure of the air. The density of substance is independent of the quantity of that substance and therefore density is an intensive variable. So let's consider a specific volume. Specific volume is the volume of a substance divided by its mass. That can also be said as the inverse of density. It's not easy to develop a concrete understanding of the concept of specific volume but in thermodynamics we use specific volume rather than density. Now the specific volume of liquid water is close to 0.001 cubic meters per kilogram and the specific volume for air is in the order of one cubic meter per kilogram. So in summary, volume and mass are used to denote the quantity of a substance. Because we use volume and mass to denote a quantity of a substance they are extensive variables. Their magnitude depend on the amount of that substance. Density can be calculated by mass divided by volume and its units is kilogram per cubic meter and also you can calculate specific volume by taking volume divided by mass. Specific volume is also the inverse of density. And we also know that density and specific volume is intensive variables, meaning that they are independent of the quantity of the substance. That's it, thank you very much for watching. The course notes which these videos are based on is available on my website, adreonsblog.com. You are welcome to connect with me on Twitter. My Twitter handle is at asv90 and if you have any questions you're more than welcome to ask them on Twitter and I will answer them. Thank you very much for watching and I will see you in the next video, bye.