 Hey everybody, Dr. O here, in this video we're going to talk about the four mechanisms of heat exchange or heat transfer. So as you can see we have radiation, evaporation, convection and conduction. So they all work in a very similar method and that is that heat is going to flow from where there's a high concentration of it to a low concentration. The four different methods or mechanisms of heat transfer just have to do with directly how it's done. So let's look at each one of them. So let's start here with conduction. So conduction is going to be the transfer of heat between two objects that are touching each other. So here we see, you can guess by looking at this picture, that the warm tea, warm coffee, whatever's in there is going to transfer that heat from the mug into the fingers. So your fingers are going to be warm if you're holding, mine's in a thermos, but if you're holding warm water, I think it's generally more with seats, right? If you sit down and the seat is real cold, now it's going to actually make you colder where you sit down and the seat is real hot, then it's going to make you hotter. So that's conduction when two things come in direct contact with each other. This is only going to be about 3% of the heat transfer that occurs with humans. So it's not a huge deal. Next we have convection. So you see here, the wind is blowing here. If you imagine you have a fan blowing in your face, this kind of thing. Convection is going to be responsible for about 15% of the heat loss from a human body. Remember where this heat comes from, just our metabolism generates it. So this is going to be, the air surrounding us is going to carry heat away from us if the air is cooler than our bodies. So if you think about it, I think about this with windshield, right? Why is it colder when it's windy? Well, we kind of have a blanket of warmth around us and what the wind does is blows that blanket off and that's why it's so much colder when it's windy. So the wind chill would be an example of increased convection, moving this warm air away from our bodies so we're surrounded by cooler air making this colder, at least that's what I think of with convection. So still not a huge deal. The next two, the last two are the ones that we pay the most attention to. And the first is radiation. This is going to be by far the most common way that your body loses heat is through radiation. So radiation is the transfer of heat through infrared rays. You see a picture of the sun here. So the sun is basically radiating us. If you're outside, I think about like in the middle of July or August or something and you're outside and it feels like the sun is literally beating down your neck because on these really sunny days that heat and radiation from the sun is actually transferring heat into you and warming you up. So we're all basically radiators. Just like a radiator in a room can warm a room up. We're basically radiators which is why if you put a large group of people together the temperature in the room would go up because we're all just sitting here furnaces just pouring out heat. So remember that radiation is the key way that we lose body heat and that's why. We just radiate into our environment with infrared rays. This is also why if you use infrared cameras you can see us because we light up because of this infrared energy being released from our bodies. And lastly we have evaporation. So normally evaporation is around 20% of the heat that's lost by a human body, especially so I would say the key thing here is radiation is the key way we lose body heat. But evaporation is the key way we cool down. So if we're overheating because it's hot out or we're exercising, evaporation or maybe it's better to call it sweat evaporation is the main way that we cool our bodies off. We do it with the fact that it takes a lot of energy to vaporize water, to remove water and evaporate it into the environment and as it does so it's going to pull a lot of water with it. Now that's how sweating works but the key with sweat besides the fact that it's the primary way we cool our bodies down when we're exercising is sweat evaporation is going to be dependent on humidity. In a low humidity situation or environment almost all the sweat you produce will be evaporated and take heat with it. But if it's humid there's already so much moisture in the atmosphere that your sweat is going to pull off of you rather than being evaporated. This is why it's up to you know they say it's up to 27 times harder to cool your body down when it's humid and we all know that 90 degrees with low humidity doesn't feel anything like 90 degrees with high humidity and that's why if you're concerned about dehydration or losing too many electrolytes super important the more humid it is the more liquid you can consume. You can lose two three thousand milligrams of sodium in an hour from sweating but if you're if you're sweating and it's not being evaporated which means that you're sweating and it's not cooling you off your body's going to generate more and more sweat. So in a human environment you make way more sweat but it's actually less effective and that's why you got to be careful with dehydration because and then if you stop sweating that's when you get in serious concerns with heat stroke because without this process how are you going to cool your body and your core temperatures go into climb and that could be life threatening. Alright so those are the four mechanisms of heat transfer just remember that radiation is the primary one and then evaporation or sweat evaporation is the primary way we cool if we're exercising or we're getting hot. I hope this helps. Have a wonderful day. Be blessed.