Introduction To Temperature Scales

by Patrick Ford
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Hey guys. So, for the next couple of chapters, we're gonna start talking about thermodynamics. And to start things off, we're gonna start talking about the most basic fundamental measurement within thermodynamics, which is called temperature. So, I'm gonna give you an introduction of brief introduction on temperature and the different scales and systems that we use in physics. Let's go ahead and check this out here. So, what is temperature? Well, we're going to develop a much more precise definition later on. But for now, a basic definition of temperature is it's a measure of how hot or cold something is. So, we can kind of rely on our everyday experience for this. If you grab an ice cube, that ice cube relative to you is probably feels very cold versus if you stick your hand in a pot of boiling water that unfortunately is gonna be very painful and feel very hot. Now, these are really precise scientific definitions. So, a more useful one is it's a measure or it's related to the average kinetic energy of the particles that make up an object. So, remember that kinetic energy is related to how fast particles are moving. So the idea here is that the molecules of water that are sort of locked up inside of an ice cube are vibrating very slowly. There are low temperature, they don't have a lot of kinetic energy and therefore the particles move relatively slowly versus the pot of boiling water. These things are actually moving around very, very, very quickly. So there's a high temperature. The things feels very hot. There's lots of kinetic energy and the particles are moving very fast. All right, so we're gonna have to do some measurements and calculations with temperature. So we're actually going to need to know the three temperature scales or systems of units that we have in physics. And they're all actually related on arbitrary reference points that have to do with water. These are basically just values that we picked because we could easily reproduce them. These are things like the freezing point or boiling point of water. Basically any scientists could freeze or boil water and that's what we chose as our reference points. So, if you live in the United States, you're probably most familiar with the Fahrenheit scale and the Fahrenheit scale has two reference points. The freezing point of water is 32 F and the boiling point is 212 F. Exactly. Now there are obviously much colder temperatures. Zero point is gonna be somewhere around here, all the way down to the coldest temperature possible. We're talking about that in just a second here. Now, the other scale that we use is called the Celsius scale, basically if you live anywhere else in the world, you probably use this one. This is sort of like the metric system temperature scale and the reference points that we use are a little bit more intuitive, basically what scientist is did is we called the freezing points. The point where ice turns to water and vice versa. We called this the zero point. This is where zero Celsius is and the boiling point. This is actually 100 degrees Celsius. So I don't want to point out is that these measurements mean the exact same thing. So for instance, zero degrees Celsius and 32 F both represent the freezing point of water. We just naming them were sort of calling them different numbers, it's kind of have like 12 inches is equal to one ft, they both represent the same distance, just on different number scales. It's kind of the same exact idea here. Alright, so the last thing I wanna talk about is the kelvin scale. The kelvin scale is the one that we're gonna use most commonly, it's the one that we're going to plug in to all of our equations, we're gonna plug in all of our temperatures in kelvin. Now, kelvin is a little bit different because it's called an absolute temperature scale and the reason it's called this is that the kelvin scale actually starts at absolute zero. What do I mean by that? Well, for the Celsius scale, we just chose zero as the freezing point of water and in the Fahrenheit scale, zero was just sort of over here somewhere. Doesn't actually correspond to anything special, but for the kelvin scale, the absolute zero, the zero point, the starting point is the coldest temperature possible. So this is actually what we define as the beginning of the kelvin scale, It's the coldest possible temperature that you could ever possibly have. Alright, and so we call this absolute zero. So the freezing point of in kelvin is gonna be 273. kelvin and the boiling point is going to be 317 uh 73.15. Alright, so what I want you to do is realize that these scales here, the difference between these two numbers is 100. The difference between these two numbers is also 100. So the kelvin and Celsius scale are actually sort of the same, it's just that one is sort of shifted downwards like this whereas this scale over here, the Fahrenheit, these differences are actually 100 eighty's. So basically you can kind of think about is that the scale is a little bit bigger. The numbers there are more numbers in between those freezing and boiling points. Alright, so we can actually go ahead and convert the coldest temperature possible to Celsius, that's gonna be negative to 73.15 degrees Celsius and Fahrenheit, it's going to be negative for 59.6 degrees Fahrenheit. Again, all these measurements mean the same thing, These are all the coldest possible temperatures just in their respective scales. Alright, so hopefully this makes sense. Let me know if you guys have any questions