If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content
Current time:0:00Total duration:9:18

First Law of Thermodynamics introduction

AP.BIO:
ENE‑1 (EU)
,
ENE‑1.H (LO)
,
ENE‑1.H.1 (EK)
,
ENE‑1.H.2 (EK)

Video transcript

let's now explore the first law of thermodynamics and before even talking about the first law of thermodynamics some of you might be saying well what are thermodynamics and you could tell from the the roots of this word you have thermo related to thermal it's dealing with temperature and the dynamics the properties of temperature how do they move how does temperature behave and that's pretty much what thermodynamics is it's about it's the study of heat and temperature and how it relates to energy and work and how different forms of energy can be transferred from one form to another and that's actually at the heart of the first law of thermodynamics which we touched on on the introduction to energy video and the first law of thermodynamics tells us that energy energy this is an important one I'm going to write down energy cannot be created or destroyed cannot be created created or destroyed or destroyed it can only be converted from one form to another it can it can only only be converted only be converted I'm having trouble writing today converted from one form from one form to another or you could transfer it but you're not going to you're not going to create or destroy it and the whole thing that I the rest of this video I just want to really have you internalize that and I want to look at a bunch of examples and think about well what is the energy that we're observing or that we're seeing in a system and then thinking about where is that energy coming from that to appreciate it's not just coming out of nowhere and that it's not just disappearing it's not getting destroyed either and so let's start with this example of a light bulb and I encourage you to pause this video think about the forms of energy that we can see here and then think about where is that energy coming from and where is it going well the most for obvious form of energy that you see here and this the whole point of a light bulb is you see the radiant energy you see the you see the electromagnetic waves the light being emitted from it and that light so this is radiant energy radiant energy and that and that radiant energy that radiant energy is due to the heat in the filament right over here as the electrons go through it it generates heat so you have thermal energy so you have thermal energy as well thermal thermal energy but where does this radiant and thermal energy come from it is once again first law of thermodynamics that tells us it's not just being created out of thin air it's it must be converted or being transferred from someplace well I just gave you a hint this thermal energy is due to the electrons moving through the filament they're moving through the filament which has some resistance and that generates heat so the electrons are moving through this and as they move through that resistor they generate heat so you actually have the kinetic energy of the electrons I'll just write ke for short kinetic energy of the electrons well where is that kinetic energy coming from well that's coming from the potential energy you know maybe this thing is plugged into is plugged into a socket of some kind so let me draw an electric socket right over here and the electric socket I'll draw the electric socket if this is the electric socket in your home there is a electrostatic potential between these two terminals and so when you make a connection the electrons are able to the electrons are able to move and we will get into the details of AC and DC current in the future but there's there's an electrostatic potential from this point to this point if we assume that's the direction that the electrons are going in and so that that that it's that potential energy we convert to this kinetic energy of the electrons which is really in the form of a current and then that gets converted into thermal energy and a radiant energy now what happens after let's say you unplug the light the light goes dark what happened to all of that energy is it still there well yeah that thermal energy is going to continue to dissipate through the system and this right over here would be an open system it's going to the the air inside the light bulb you can't fully see the light bulb right here but it looks something like this that's going to heat up but then it's going to heat up the glass rounding the lightbulb and that's going to heat up the surrounding air so the thermal energy is going to be transferred to that radiant energy is going to move outward and it could be used it could be converted into other forms of energy most likely thermal energy it is also probably going to heat up other things well what about a pool table when I hit a when I had it what if I hit a pool a billiard ball or a pool ball right over here well where is that energy going well that some of that energy might be going to go hit the next ball which might go to hit the next ball but as we all know if we've ever played if we've ever played pool at some point they're going to stop so what happened to all of that energy well while they were rolling while they were rolling there was some air resistance there was some air resistance so they're bumping against these a the air molecules and it's really friction due to air and that energy is essentially going to be converted to heat and one trend that you're going to see very frequently is as systems as systems progress a lot more of the energy tends to tends to turn into heat rather than doing useful work and so you're going to have as the billiard balls move there's the air and so that's going to be that that's going to be converted that some of that kinetic energy is going to be turned into heat energy you're also going to have friction with the actual felt on the table and that friction you're going to have molecules rubbing up against each other that's also going to be converted into heat and so that because that that kinetic energy gets sapped off of a Keith gets keeping sapped away from the friction which is essentially converting the kinetic energy to heat energy eventually you won't have any more kinetic energy now what about this weightlifter here he's using the chemical energy in his in the ATP in his muscles too that converts into a kinetic energy that moves his muscles that moves this weight but once he's in this position what happened to all of that energy well a lot of that energy is now being stored in potential it's the potential energy he's got this big weight he's got that big weight above his head and if you were to let just let go that thing would fall I wouldn't recommend he do that but that thing would fall quite fast and so now it's all or a lot of it has been stored up in potential energy but he would have also generated Heat his muscles would have generated heat even the act of moving at the air is going to be some heat in the air some friction with it and so I want you to appreciate that this energy is not coming out of nowhere it's it is it is being converted from one form or another are being transferred from one part of the system to another now we can look at these examples over here same thing with a runner what happens after you can you can by the fact that okay his chemical energy is allowing his muscles to move and that's turning into his whole kinetic energy for his entire body his body is moving but at some point he stops where did all that where did all that energy go well some of it will be heat in his body that's being dissipated into the broader system into the air and also when he was running there would been there was this contact with the ground that's going to make the molecules in the ground vibrate a little bit some of it will be transferred as sound so the air particles moving through the air and a lot of it will be heat and we're going to see that over and over and over again the diver up here you have mostly potential energy then it converts to kinetic energy as he's as he's get almost in the water but what happens once we falls into the water well then that energy is going to be transferred as you're going to have these waves of water move away and it will also increase friction so well actually you would have had friction as he fell down so that would have generated some heat and it would have been also some heat with the friction with the water you normally don't think of friction with the water but there is some friction with the actual water and there's also your these waves you have higher kinetic energy of the actual water being transferred outward from where he actually dropped in and I could keep going on and on you have the potential the chemical potential energy of the fuel here being trans B you have combustion occurring and then that gets converted into the thermal energy and the radiant energy of what we associate with fire and that doesn't disappear it just keeps the radiating outwards the radiant energy just keeps reading outward maybe it might heat up something and the thermal energy will just keep radiating outward and or May I should say the thermal energy will just dissipate outward and heat up the things around it same thing with our lightning example you start with the electrostatic you started with this electrostatic potential where the bottom of the clouds were more negative and then the ground is positive as well and at some point that potential energy turns into kinetic energy as the electron transfer through the air and then that gets converted into or to a good bit it's going to be converted to heat and radiant energy so the whole point of this video is no matter what example you look at if you look if you think about it carefully enough and I encourage you to do this in your everyday life the energy isn't just coming out of you know magically appearing it's it's just being converted from one form to another
AP® is a registered trademark of the College Board, which has not reviewed this resource.