 For chapter one, we are focusing primarily on defining terms and making sure that we understand properties well enough to be able to use them to define systems. First of all, it's important that we establish what we are trying to do in thermodynamics. Thermodynamics is the study of energy and primarily for our purposes quantifying it. We are playing energy accountants. We are trying to keep track of inputs and outputs so that we can come to an idea of what's happening to the whole If you started your week out with $50 and you spent $20 and you gained $10 you would end your week with $40 Similarly if the error in the room that I'm sitting in has 50 kilojoules of thermal energy and it gains 10 kilojoules by me sitting in it and talking to you and 20 kilojoules are lost to outside the energy in the room would have dropped 10 kilojoules When you're talking about thermodynamics, there is a little bit of a distinction between microscopic versus macroscopic thermodynamics and that pretty much comes down to a difference of perspective You can think of it like the difference between Lagrangian analysis and Eulerian analysis microscopic thermodynamics typically looks at the state of individual atoms or molecules and then you come up with an assessment of the whole by summing together all of the individual molecules You are looking at a kind of statistical perspective Macroscopic thermodynamics is the perspective where you are looking at the entire thing If you are considering an entire system by looking at its boundary with the outside world as opposed to looking at what's happening on a very small Quantum of energy and then adding them together. That is a macroscopic perspective Our perspective is going to be primarily macroscopic You may be familiar with some of the laws of thermodynamics We are going to be using the first and second primarily as well as I guess the zero with for our purposes The zero with law of thermodynamics means that if two things are in thermal equilibrium with one another say A and B and Then one of those is an equilibrium with something else say B and C Then the first thing and the last thing must also be in thermal equilibrium with one another So if A and B are in thermal equilibrium and B and C are in thermal equilibrium Then A and C must also be in thermal equilibrium That's a very long-winded way of saying that if you're holding a thermometer inside and it reads 71.0 degrees Fahrenheit and you take it outside and it reads 71.0 degrees Fahrenheit then Everything else being equal the temperatures must be the same in both places The first law of thermodynamics you must be familiar with already. It is the law of conservation of energy It says that energy can be neither created nor destroyed It is so useful that we often just refer to it as the law of conservation of energy But it is the first law of thermodynamics When we apply a first law perspective to one of our analyses What we're doing is saying well, what's happening to the energy in this situation? We know it can't be created and it can't be destroyed. So where did it go if? Five kilojoules enters a system and two of it leaves Then three kilojoules must be left in the system The second law of thermodynamics is focused on the quality of energy It says that energy has a magnitude, but it also has a quality That quality represents the usefulness the order of the energy And it also says that energy will naturally go from a state of order to disorder To bring it from disorder to order requires an investment of energy So an example of that would be to say Electricity is a higher quality energy than thermal energy. So it's easy to go from electricity to heat We can get almost a hundred percent of our investment Because the conversion happens very easily It's easy to convert from a state of high quality energy to low quality energy But to go from low quality to high quality from say heat back to electricity We have to invest something in the process There is no way we're going to get 100% of the energy in heat to electricity We pay a cost for that conversion Another common question at this point is what is energy? For our purposes here, it is best to describe it as the ability to do useful work The best definition of energy from a physics perspective is probably that thing that is conserved when nature happens But that's a little bit harder for us to wrap our heads around We are applying energy terms to a specific problem in front of us Similarly, it is not uncommon to consider heat as a type of energy And it used to be that heat was the only type of energy But we now know that heat is just one of many types of energy and furthermore We clarify that when we are talking about heat. We are usually talking about heat transfer Heat transfer is dynamic When heat is in something, we actually call it thermal energy. That's the static equivalent So if my cup of coffee is hot It would be described as having a high thermal energy which would manifest as a high temperature But the heat that it gives off is a rate of energy exchange between the coffee and its surroundings It is heat transfer when it is going from the system to its surroundings When we are quantifying the characteristics of a system We are going to be describing those properties using units and units are an indication of a quantity within a dimension So here it's important that we take a minute to talk about dimensions and units for our purposes, we are going to describe dimensions as primary and secondary a Primary dimension is something that is directly measured and cannot be reduced further We describe four primary dimensions mass length temperature and time But there are more we just don't consider them here. They are outside the scope of our analysis Secondary dimensions are dimensions that are made up of the primary dimensions for example volume Is a secondary dimension and it is made up of length cubed. It is made up of primary dimensions force is Another secondary dimension you could describe force as a mass times acceleration Acceleration would be length per time squared therefore the force dimension would be mass length per time squared pressure is a secondary dimension that would be force per length squared Which would be mass per length time squared when we are describing dimensions we are usually quantifying something with units and Just a note all units are arbitrary They are not better or worse than each other, but there are different units that are more useful in different circumstances For example when we talk about weight A Newton is a manifestation of force that is convenient for calculations because the metric unit system is built So that those calculations are very convenient However, if you were a 17th century farmer a Newton is a very abstract concept The pound is defined as an quantity of wheat. I Believe it's seven thousand, but don't quote me off the top of my head a Pound of force would be the weight of seven thousand grains of wheat Taken from the middle of the ear and if you were a farmer and you were trying to figure out how much wheat you had You could describe it in pounds of force That would be more convenient to that person than the Newton Same goes for temperature scales When we talk about temperatures, we usually use a relative temperature because it's a little bit more convenient When I'm describing outside temperature. I could describe that as 300 Kelvin, but that doesn't give a lot of relative perspective between a high temperature and a low temperature 300 Kelvin versus 350 Kelvin is a lot of temperature difference, but it doesn't seem like much in regard to numbers The logic of the Fahrenheit temperature scale any more is that zero represents About the coldest condition that you are going to encounter at least if you don't live in a lot of very unfortunate places in the world like for example where I am now and 100 represents about the highest temperature that you're going to be considering again unless you live where I live and Therefore you can compare the cold temperature to the hot temperature with a relative scale between them If I say it's 25 degrees Fahrenheit outside and tomorrow it will be 75 degrees Fahrenheit You can make an easy correlation between. Oh, that's going to be very hot relative to what it is now It's going to feel like much hotter than the difference between 300 Kelvin and 325 Kelvin Same goes for Celsius for Celsius. We are describing the hot and cold relative states of water So if zero is the temperature at which water freezes under standard atmosphere pressure and 100 is the temperature at which water boils under standard atmosphere pressure Then I can easily see how the water in front of me is behaving relative to its freezing and boiling points if I put a Pot of water onto the stove with which to make ramen noodles and it begins at 20 degrees Celsius And I heat it up and it goes from 20 to 30 and then from 30 to 40 I can easily see ah I'm like 20 percent boiling now. I'm 30 percent to boiling or 40 percent to boiling I am half way between freezing and boiling when I'm at 50 degrees Fahrenheit That is the usefulness of that temperature scale now for math purposes Neither one of those is good If it's 25 degrees Fahrenheit outside and I say tomorrow is supposed to be twice as hot What does that mean? Is it 50 degrees Fahrenheit? Okay, then what about if it was negative five degrees Fahrenheit? Does that mean tomorrow's twice as hot? So it's negative 10 No for math. We are talking about temperature relative to absolute zero That is actual manifestation of average kinetic energy of the molecules, which is what temperature actually means We're describing it relative to when there is no motion So if it's 300 degrees, excuse me if it's 300 Kelvin out and Tomorrow it's supposed to be twice as hot twice the thermal energy would mean 600 Kelvin That would be a very hot day by the way furthermore when we are talking about units the Arbitraryness of the units pretty much comes down to what's useful for the problem in front of us But something else to be aware of is that when you are adding and subtracting units You need them to be the same the fancy word for that is dimensionally homogenous You can't add five kilopascals to five psi to get 10 kilopascal psi You need to convert one to the other or rather you need to convert them so that they're the same so that you can add them together when we are keeping track of units and dimensions in our calculations, we are going to be using a representation a notational scheme called dimensional analysis Where we keep track of the dimensions or rather we keep track of what's happening to the dimensions relative to one another and That makes it much easier for us to convert to different unit systems or even to see where we possibly could have made mistakes Let's explore that more now