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Current time:0:00Total duration:10:50
Sal wrote "subtance," but meant to write "substance."

Video transcript

in chemistry there is a very valuable concept called specific heat is the specific heat is particularly a given substance so every substance has a different specific heat and it's defined as the amount of heat the amount of heat energy needed to raise one gram of a substance one degree Celsius sometimes the definition might say to raise a given mass of a substance one degree Celsius but I'm just being a little bit more a little bit more particular one gram of a substance one degree Celsius so it's telling it says well how much energy do I have to put into something to heat it up so for example for example water water if I want to raise that one degree Celsius so if I want to raise that one degree Celsius I would have to put in I would have to put in a certain amount of I would have to put in a certain amount of heat which would be different than si if I had sand let's say this is let's say this is sand this is sand right now I have trouble picking colors so this is sand right over here I could do a better job of drawing sand so this is sand right over here if I want to raise that one degree Celsius I would need a different amount and it actually turns out that I need less heat I need less heat to raise the sand one degree Celsius that I need to raise the temperature of the water or one gram of the water one degree Celsius so let's say this is a gram of water and this is a gram of sand I'm going to need more heat here to raise this one degree Celsius than to raise that and that's because water has a higher specific heat so higher higher relatively higher specific heat specific heat and sand or at least relative to water has a lower specific heat lower specific heat so two ways you could think about it let me write this lower lower specific specific heat two ways to think about it if you want to raise one gram of each of them one degree Celsius you're going to have to put more energy into the water then you're going to have to put into the sand or the other way around if you put the same amount of energy into both you're going to raise the temperature of the sand lot more than you would raise the temperature of the water and water actually its specific heat has a special name and this is a name that you have seen before the specific heat of water is called the calorie specific specific heat of water is called the calorie and you have seen this word before when you've when you've wanted to cut calories when you've looked at the back of nutritional labels on on food now there's one clarification the calorie that people talk about when they're talking about nutritional labels or how many calories are actually in food that's actually kilocalories so if you see if someone hands you a let's say bowl of ice cream let me draw a bowl of ice cream here so if someone hands you a bowl of ice cream right over here and they tell you that this is 500 calories let me write that down this is 500 calories if we're thinking of it in terms of specific heat it's actually 500 kilocalories 500 kilo kilo calories so there's a couple of ways that you could think about 500 kilocalories you could think about it as this is this this ice cream has enough energy to raise to raise 500 500 kilograms of water water 1 degrees Celsius you could also view it as the amount well actually if you want to think of it in more human terms most humans are roughly grown people are between say 50 kilograms or 60 70 kilograms roughly over there so you could say 50 kilograms of water actually a grown male might be composed of about 50 kilograms of water there's obviously other things that make up their weight I'm just approximating 50 gram 50 kilograms of water and then we're raising it one degree Celsius in the top case but in this case you would raise it 10 you would raise it 10 degrees Celsius and that's actually happening in our body your body heat is actually caused partially your the energy from food some of it is to process your movement and the different functions of your muscles and the brain and all the things your body does and some of it it just is just producing heat sometimes as a byproduct of that movement and sometimes frankly just for the sake of producing heat so 500 500 calories that you see on a food label that's really 500 kilocalories and that's the that's enough energy to raise 500,000 grams of water remember 500 kilograms 500 thousand grams of water one degree Celsius or fifty thousand grams of water 10 degrees Celsius but anyway water has a special name it's calorie it's neat to be able to connect it to or what we're eating and to think about what a calorie actually means or what a kilocalorie actually means but this that this this notion that water has a higher relative specific heat to say things like land actually has huge impacts on our climate and it's actually one of the reasons why it's often nice to live near the coast because let me draw let me draw a coastline right over here so this is actually I'll draw it from I'll draw it from above so that's the coastline this is land let's just say it's made up of sand for the sake of argument and other things and this is water and let's think about it first let's think about it in the summer let's think about in the summer when it is hot and you think about just a sunny a sunny day so in the summer when things are hot so you have the Sun you have the Sun right over here and it's radiating energy and obviously the air it also has is is also warming up the things that it comes in touch with but you're having at least at the coastline the air is roughly the same temperature over both and although there will be some variation and they're getting the same amount of sunlight but since water has a higher specific heat that heat is going to what is going to warm up water or less so this is going to get less hot let me write it over here this is going to get less hot less hot and the land is going to get more hot more hot more hot and that's why when you're in the coastline the air is also affected by what's in touch with it's going to be in touch with this less hot water and so as the air especially if it's coming from the ocean if the air is going in this direction then if you're at the coast you're going to get probably a cooler breeze and if you're more inland over here if you're more inland over here it's probably going to be a lot the air is going to be hotter so this is going to be hotter air if you're inland and it's a less hot air if you're at the coastline because the air is being cooled down to some degree or it's not being warmed up as much by the water now you have the opposite effect if you think about the coldest times of the year if you think about the middle of the night in the winter so let me draw that so if you think about nighttime in the winter when everything is cooling down when everything is cooling down once you have your coastline well now they're both the land over here and the water they're going to be radiating heat and the water is going to be radiating heat there's no other sources of heat that's radiating heat into the air but if they if they radiate roughly the same amount of heat the land is going to look drop in temperature much much more so it's going to get colder here so the land is going to be get colder and the water is going to get less cold because it works in both directions more energy goes into water the temperature changes less and it could also radiate the same amount of heat but also lose less it would also lose less temperature so in the winter and really cold times of the year well the air above the water when it comes in touch with the water is going to be less cold than the air above the land because the water is less cool and and so it's nice to live near the water it's going to be less cold in the coastal areas than it would be if you're further inland and this this phenomenon this is frankly anywhere where you might see water but it's very pronounced where I live I live in the San Francisco Bay Area and if you live you literally have this you have the Pacific Ocean let me draw that you have the Pacific Ocean here you have a ocean right over here and you have the San Francisco Bay that looks something like that you have your Golden Gate Bridge is right over here for anyone who is curious this is San Francisco right up here I actually live right right about there and you see it if you if you hang out in the summer in the middle of the day in the coastline it could be maybe ten ten degrees even 20 degrees cooler than if you are well inland over here so it has very a profound impact on weather patterns so the last thing you might be wondering is well why does water have such a high specific heat well that goes back to our good old friend the hydrogen bond because if you're talking about a solid substance if you're talking about a solid substance and I'll just draw a generic solid substance so a solid substance right over here I don't know what this is let's say it's in some type of structure that looks something like this as it gets energy as it gets as it gets heat energy the heat energy just increases the kinetic energy of the actual particles it actually just makes them vibrate more makes them vibrate and place more and that's actually what temperature is it's really average kinetic energy when you touch something like ooh that's hot it's really because those things are just vibrating Ritsu super super super super fast so it's going to make these things vibrate more almost in place especially if we're thinking about something that is a solid while in the case of water sure when you get more energy it's going to make the water molecules move around faster vibrate more have more kinetic energy but in order to have more kinetic energy they're going to have to overcome this kind of creation and and-and-and-and-and breaking up of the hydrogen bonds you can almost imagine the friction of a hydrogen bond that bond you can imagine if if this water molecule wants to move in this direction has to break this hydrogen bond is going to form another hydrogen bonds got to break that and so it needs energy to keep breaking and ream or at least breaking those hydrogen bonds overcoming the friction of those hydrogen bonds and I'll use I'll use the friction in quotes because it's well actually all friction is actually some type of atomic force that's occurring at a microscopic level but it's having to overcome that and so some of this heat energy is actually used to overcome that as opposed to increasing the actual kinetic energy of the individual molecules or making them vibrate or whatever it actually increase their temperature and this is why water is able to store more heat and why it has a higher specific specific heat
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