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Current time:0:00Total duration:7:01

Video transcript

in the video on the second law of thermodynamics I talked about how the entropy of the universe is constantly increasing that it's not going to decrease and another way of thinking about it is is that the energy in the universe more and more of it is going towards entropy it's becoming less and less useful and the argument that I use even in our everyday I talk about hey while I'm making this video my body is generating heat and that heat is leading to entropy it's leading to more entropy in the universe and an a reasonable question is how does heat lead to entropy and remember heat is a transfer a transfer of thermal energy and entropy this is a state of the system it's the number of it's it's the noise it's a it's the amount of disorder we have is the number of states that the system could actually take on so let's have an example here all right let's say assume that this is an ideal closed system this little white square here and these molecules are bouncing around with some temperature so they have some average kinetic energy each molecule will be doing different things and I always draw it as this translational kinetic energy but they could be rotating and oscillating and doing all sorts of other things so they could be they could be doing other things as well but the translational kinetic energy is a little bit easier to actually visualize but now let's transfer some heat into the system so we have a transfer of thermal energy which we call heat let me pick a color for that I will use orange and we use a letter Q to denote heat so we have a heat transfer coming into this and then because of this the temperature of this system goes up the average kinetic energy goes up these things start bouncing around with more with more momentum with more velocity so why does this system have entropy you might say well look you know there's they'll have the same number of molecules I have the same amount of volume I'm looking at a two dimensional looks like area but we could imagine the same amount of volume that it's filling up it feels like there's the same number of places that the actual molecules could be but our state is not dictated purely by position not purely by where the different things are it's the state is everything about the system that you could use to predict what's going to happen next to the system so the state also includes the various velocities of these particles so you when you have a higher temperature you have a larger number of potential velocities that you might be able to actually take on and also when you have this higher kinetic energy remember all of these all of these molecules they at the end of the day they're you know they're made up of atoms that have nuclei and they have electrons buzzing around them and as a if they don't have much kinetic energy they might not be able to get too close so let's say this is the outer electrons of one I'll just say atom and let's say that this is another one right over here if they're going with only a reasonable kinetic energy if they go with a reasonable kinetic energy they might be able to get maybe there they're going to be able to get that close but if there if they were running if they were hitting each other much faster they might be able to get a little bit closer they might they might they kind of might kind of smush into each other if you imagine kind of two balls hitting each other much faster they're going to push on each other a little bit harder and so there's actually more possible States you can take on when you have higher kinetic energy so this is this is you know these things came in really really fast and smushed into each other while these were nice and polite and came in at a nice gentle at a nice gentle velocity so you can actually even have more positional States more more different configurations in three-dimensional space so that's why heat is actually leading to entropy now I know what some of you might be saying well heat doesn't only heat doesn't only caused disorder in fact he can be used to do work in fact that's the whole basis in fact a lot of the basis of the Industrial Revolution steam engines combustion engines the combustion engine in your car that uses heat uses a combustion reaction to to expand to expand to push up a piston which is used to do actual work and that is act that is of course true and over here we have an example of that happening so I have some I have some molecules in here buzzing around some temperature and then I'm going to apply and we're going to add some heat to the system so let's add some let's add some heat to the system and in this system I don't have just a closed boundary these things start buzzing around more they can take on more states and all of that type of thing but they can also use to expand the container so what we see happening here is they push this piston they push this piston open you actually have work you actually do work in a different color you actually have work being done you actually and I'll do it smaller you actually have some work being done and how is that working done well as these things bounce around and we're talk about a lot of molecules every now and then one of these molecules is going to bump there and then bounce off but that's going to provide some force for a very small amount of time that's going to push it up a little bit and but you have so many of these molecules to it I've only drawn a handful of them but in any real thermodynamic system you're going to be talking about many you know many millions and millions and millions you're talking about things on the multiples of Avogadro's number number of molecules and so at any given moment a lot of them are going to be bouncing right off of this thing they're going to be doing work they're going to be pushing they're going to be displacing this piston in the direction of the force or part a component of their force is going to be pushing this piston actually up and doing work but no no heat based I guess you could say system or engine can be 100% efficient so some of this can be used to do work but a lot of it is going to be used to add to the disorder of the system to increase the number of states that the system could take on one way to think about it and this has always helped me is heat heat is transfer of thermal energy that happens at the boundary of the system this heat could be you know maybe there's a maybe there's a flame down here and at the boundaries this thing might be able to if this wasn't a fully closed system it could release heat at the boundaries of the system but within the system the the heat is just leading the increased thermal energy is just leading to more entropy now work also happens at the boundary of the system so up here there's probably some heat being released but it's also able to do work so heat and work these are happening at the boundaries of the system but a lot of that energy goes into the inside of the system and that is just things are just going to you know is like a big mosh pit these things are going to run into each other much faster and way more states that they could take on and so that's why when I talk about you know I move around and I'm walking on the floor just the friction with the carpet is going to generate heat that's going to contribute to entropy in the universe just me existing the cellular processes in my body to generate heat it increases the entropy of the universe that makes the the total energy of the universe less useful that's why it's happening
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