let's the second thing we can learn from the spectrum it's the temperature we can tell what the temperature of an object is based on the pattern of light it's giving off so here's my question what is temperature when we talk about the temperature of something what are we talking about what what are we actually measuring about that object if we're talking about temperature what is what does temperature mean yeah how hot or how cold something is how hot or how cold something is but it turns out that's not actually what you're actually measuring okay it turns out what you're actually measuring when you're talking about temperature like how hot and how cold is kind of like how we're feeling and somebody's on the right track right there what you're actually measuring is the random motion of the particles of a substance okay and we don't normally think of it that way because the particles of a substance are very very very small in microscopic right but you know let's say that I was the particle in a substance if you look soo min far enough that you could actually see me I'm not just sitting here like if we look at the air in this room or your room or wherever you're at the air particles aren't just sitting still there they're jiggling around right they're jiggling around now does anybody know what happened what a high temperature means does anybody know what happens to these jiggles if we were to raise the temperature of this gas what happens to these random jiggles yeah they go faster so a higher temperature would be something like this and a lower temperature if you could see the particles they're jiggling around slow so that's what temperature is okay what unit are we gonna use for temperature most of the time well what's the what's the dumb everyday unit of temperature that Americans use what's the dumb unit of temperature that we use maybe dumb is a bit strong yeah don't worry if you can't spell it Fahrenheit right Fahrenheit Fahrenheit is is not a very good system to use for temperature and to understand that we need to know what is Fahrenheit based on okay because every thermometer is basically the same like you if if you all thermometers yeah I mean like just think of like a typical thermometer like a classic thermometer it's just a tube of glass with a substance in it that fills it up as it gets hotter so you uh you couldn't use any system on that same thermometer they're all basically trying to tell us the same thing but let's say you had a blank one and you wanted to set it up as a Fahrenheit thermometer does anybody know what the reference temperature and by that I mean the temperature that the thermometer is based on for Fahrenheit you guys know what Fahrenheit was originally set up based on like you needed to have something with a known temperature that you could stick the thermometer in to know where to put the markings it's based on human body temperature or at least it originally was based on human body temperature so it was originally set up so that a human body would be a hundred degrees Fahrenheit right and if you had a blank thermometer you could turn it into a Fahrenheit thermometer by sticking it in your mouth and then mark your temperature as a hundred degrees does anybody know why that's a bad thing to base a thermometer on why would it be a bad idea to base the markings on your thermometer on human body temperature why would that be bad it's like some people are getting it yeah because when you base your thermometer on a reference temperature you need it to be on something that stays the same then we have two problems and you guys have pointed both of them out number one your body temperature changes throughout the day so depending on when you set up your your thermometer you'd get a different temperature set marked as a hundred degrees and also every person is different so every person who sets up that thermometer is gonna get a different temperature and you can do things to make that better like you could take a group of people and get their average temperature but that's still no guarantee that the group that you contain is is all gonna have you know maybe you didn't know it but a lot of them were sick right so human body temperature doesn't make sense to base your thermometer on so Fahrenheit thermometers are not guaranteed to be the same and we've changed what that's actually based on it's based on something else for modern Fahrenheit thermometers but it's still not gonna be a perfect match okay so fahrenheits not that great what scientifically then the only reason that people in the US like Fahrenheit is because that's what we grew up with it's like inches and feet we grew up with it so we're used to it so we kind of know if somebody says 70 degrees Fahrenheit you know roughly what that is right but if we had just grown up with a better system that's the one that we would have been used to and what is a better temperature scale that's used by most of science what's a better temperature scale actually some of you guys mentioned it earlier Celsius is better right Celsius is better degrees Celsius are better and it's better because of the the reference temperature for Celsius being a better thing to basic they thermometer on right so here's my question do any of you guys know what the Celsius thermometer is based on like does anybody know what we base like zero degrees and a hundred degrees on for the Celsius thermometer it's not the human body it's a type of substance super important substance it's water right its water and B to be a little bit more specific zero degrees is the temperature that water freezes at and a hundred degrees is Tim the temperature water boils at so if you want to set up a Celsius thermometer you can just get a bucket of water put the thermometer in it raise the temperature until it starts to boil mark that as a hundred and then lower the temperature until the water freezes and Mark that as zero right when it freezes and yeah that's gonna be a lot more reliable right because if I have a bucket of water and you have a bucket of water and we're setting up those thermometers right here we're gonna get the same temperatures on the thermometer so if we try to do experiments with these thermometers we need them to be the same so that we can compare results if they're not the same no results can really be compared and that's a lot better so you can get a much more reliable thermometer using water but it's still not perfect it's still not perfect and to understand that right now not everybody in this class lives in the same place right now - excuse me not everybody in this class lives in the same place do any of you guys like right now where I live we're basically sea level is anybody any you guys live somewhere where you're kind of above sea level I'm gonna guess probably not many of you because you're probably all kind of near me but if you did does anybody know what happens to water when you try to boil it at a really high elevation like up in the mountains like Colorado or something then we know what happens when you try to water boil water there it boils at a different temperature yeah it boils at a different temperature and that's because it turns out boiling temperature for water depends on air pressure okay because the air pressure is different up at the top of a mountain the temperature that as I air pressure is different at the top of a mountain the temperature water boils at and freezes at is going to be different and so that means if I set up my thermometer here at sea level and you set up your thermometer over in Colorado we're gonna have different thermometers again so it's not perfect but it is a lot better than using something like human body temperature instead there is an even better temperature scale and that's the one that's typically used in astronomy most of the time although don't worry I will say some temperatures in Fahrenheit as we go along but does anybody know what that last scale is what's that last scale that's even better than Celsius Kelvin okay and I'll write that down because not everybody knows that one so this is one that's pretty much almost exclusively used in science and the reason that scientists like to use Kelvin for temperature instead of Fahrenheit and Celsius is that it is a lot more exact okay and that's because of what it's based on okay now what is it based on it turns out remember temperatures about the jiggles temperatures about the jiggles in the substance right Kelvin is actually based on a special properties of a special property of the jiggles itself okay so what I want you to imagine is imagine we took the air in whatever room you're in and you know that we got these random jiggles going on what did we say happens to those random jiggles if we got the air colder if we got the air colder what's going to have - these jiggles don't make me jiggle around Petula yeah they're gonna slow down right they're gonna slow down and if we kept lowering the temperature of this substance that jiggle would slow down even more right and eventually it would probably turn into a liquid and then a solid but even in a solid there's still a little bit of jiggle in there it's just really slow but let's say I keep lowering the temperature it would keep getting slower but if I keep lowering that temperature what would eventually happen to this jiggle it would stop and then here we go you can't be any slower than stopped so that means the air in your room has a lowest temperature it could possibly have where you can't lower the temperature any less than that right now it turns out we can do that for any substance for any substance sorry I'm getting another another case of freezing display haha okay now if we took water instead its jiggling right if we lowered the temperature of the water that jiggle with eventually stop so there's a lowest temperature for water too and if we took an even totally different substance like gold there's a little bit of jiggle inside every piece of gold if we got that gold cold enough we could find a lowest temperature for gold so every substance if you lower their temperature enough all of their jiggles will stop and then that's the lowest temperature you can make that substance now it turns out what we've figured out is that that lowest possible temperature is the same temperature for every substance every substance that exists has the exact same lowest temperature and that means that nothing can go lower than that one certain temperature that's the minimum possible temperature for the universe does anybody know what we call that minimum possible temperature for the universe yeah all the particles stop at the same temperature I'll go ahead and tell you what it's called it's called absolute zero okay it's called absolute zero yeah and actually somebody got it little a good job good job so that temperature is what Kelvin is based on and it turns out it doesn't matter what the substance is is the substance is made out of and it doesn't matter where it is or what pressure it's in or what the properties around it are at all the lowest temperature is always exactly the same so if you base your thermometer on that then your thermometers would always be the same and so that means that Kelvin thermometers are always identical okay so to distinguish between those things like Fahrenheit and Celsius are called relative temperature scales because you're not always gonna get the same thing it depends on the situation but Kelvin it's called an absolute temperature scale because it's based on something that never ever changes so Kelvin temperatures are what's typically used in science but especially when you need the temperature to be really precise now check this out check this out there's a benefit here if we make the absolute bottom temperature zero Kelvin what kind of numbers do we not have to deal with in that temperature scale if Kelvin if the lowest possible temperature is zero what kind of numbers do we not have to worry about there are always a pain in the butt negative there's no negative temperatures in Kelvin so all you really got to know here is that a bigger number in Kelvin just means a hotter temperature okay so for example here we go let's say we had a and object a and object B an object a was 500 K and object B was 2,500 K so 500 Kelvin and 2,500 Kelvin don't overthink this which one of these is hotter or B which one's hotter yeah yeah B is hotter because it's got a higher number of Kelvin okay oh and by the way a lot of times people forget that this is a temperature because they're not used to Kelvin and also because there's something missing here that we normally see on temperature scales when we talk about Fahrenheit and Celsius it's always 35 degrees Fahrenheit and you have that little circle right same thing with Celsius 35 degrees Celsius but in Kelvin we don't say degrees okay we just say Kelvin so this can be read as 500 Kelvin or 500 kelvins both of those I've heard is as acceptable but just remember when you see just a capital K after a number you're looking at a temperature