- LeBron Asks: Why does sweating cool you down?
- Evaporative cooling
- Heat of vaporization of water and ethanol
- Specific heat of water
- Liquid water denser than solid water (ice)
- Specific heat, heat of vaporization, and density of water
- Temperature and state changes in water
Evaporative cooling. Why sweating cools you down.
Want to join the conversation?
- What happens if your body DIDN'T have sweat glands? Would you burn up? Or would you be cooled some other way?(9 votes)
- Dogs don't have as many sweat glands as we do, so they lose heat by panting - that's when you see dogs breathing heavily with their tongues hanging out.
Heat can also be lost in humans and other species by vasodilation. This is where blood vessels dilate, bringing hot blood to the surface of the skin where it can be cooled by the air before being returned to the heart.(16 votes)
- Is it a disease if you don't sweat or can't sweat?(6 votes)
- What makes the average temperature decrease?(5 votes)
- Since the fastest moving molecules vaporize, the temperature is lower because it adds to the average speed. When it is gone, the average speed drops, so the temperature also drops.(2 votes)
- is there any other natural ways your body cools you down besides sweat?(3 votes)
- Even if your body would be completely dry, the molecules of your skin would still transfer some kinetic energy to the surrounding air molecules. So if you are in a cold environment without an isolating layer of clothes on your skin, you will lose heat even without sweating. Also, you lose some heat by breathing (although this is technically the same process as your lungs also "evaporate" water into the air you exhale). Dogs cool down by panting with their tongues hanging out because they can't sweat like humans do.(6 votes)
- If you heated a solid block of, lets say some sort of metal(one that could withstand A Huge amount of heat), eventually would, you see the whole block vibrating?
Thank you.(2 votes)
- Yes, those vibrations are released in the form of light. Hence why when you heat up an object, it starts to glow.(6 votes)
- At5:13Sal mentions that the water molecules on the skin surface are linked by hydrogen bonds. Would the cooling effect of a liquid be different if there was no hydrogen bond? I would assume that evaporation of other liquids without hydrogen bonds would take away less energy (=heat), because not having to break up a hydrogen bond would need less energy? Am I correct?(3 votes)
- Yes, hydrogen bonds take energy to form, and actually take a larger amount of heat to disrupt a hydrogen bond putting hydrogen bonds. So in theory other liquids with the same evaporating temperatures would take less energy.(3 votes)
- At1:08, Sal says that sweat is mainly made up of water, so what are the rest of the constituents of sweat? I know that since sweat tastes salty, it has a salt content (NaCl), but what else it has along with water and salt, no matter how small the quantity?(0 votes)
- i found this at Chemistry.about.com... hope it helps!
Perspiration consists of water, minerals, lactate and urea. On average, the mineral composition is:
sodium (0.9 gram/liter)
potassium (0.2 g/l)
calcium (0.015 g/l)
magnesium (0.0013 g/l)
Trace metals that the body excretes in sweat include:
zinc (0.4 milligrams/liter)
copper (0.3–0.8 mg/l)
iron (1 mg/l)
chromium (0.1 mg/l)
nickel (0.05 mg/l)
lead (0.05 mg/l)(8 votes)
- Is water and sweat always used to cool yourself down or heat?(2 votes)
- Sweat can also be used in other situations than for cooling or heating. When we are stressed or frightened, we tend to sweat a lot. The sweat has unpleasant odor that is considered to be a social signal in threatening environment. It is believed to be an evolutionarily acquired trait to warn someone that there may be a danger there.(3 votes)
- Why do the water molecules not have the same amount of kinetic energy?
And why can we see sweat in a liquid state on our body if the water evaporates as a gas?(2 votes)
- The simple answer to both of your questions: temperature.
For your first question, each water molecule has a different temperature, and so that is what gives them different amounts of kinetic energy.
Second question: Remember that the difference between H2O in a liquid state and a gaseous state is the temperature. So, the temperature of the liquid state of water must change in order for it to become a gas.(1 vote)
- Hello! This is so incredible and so crazy to find out. I would like to know how our bodies will cool down when we dive into a pool, for example. In that case, there will be no evaporation, right? Thank you!!(2 votes)
- Evaporative and non-evaporative cooling works partly because water is a conductor(1 vote)
- [Voiceover] So if you are like most of us, your body probably sweats when it is warm, when your environment is warm, and you probably realize that it sweats in order to cool itself, in order to keep the body from overheating. But you probably have wondered, "Well, how does this work? "What is actually causing that?" And the simple answer is it's happening-- or what's allowing your body to cool-- the chemical process, I guess you could say the physical process is happening is evaporative cooling. Evaporative cooling. Which is really the notion that as that water, those beats of sweat vaporize, it's actually gonna cool your arm down. But that begs the question, how does that actually happen? And so let's just visualize it a little bit. Let's just say that is your arm, so this is your arm right over here, so let's... I don't draw my best... Draw a quick arm right over here, so okay, that's your arm, and it's got beads of sweat. Let's say it's a hot environment it's got beads of sweat right over here. And if we were to zoom in on that sweat, if we were to zoom in on that sweat, we would see the constituent water molecules and sweat is mainly H20. It is mainly water. Now when we talk about the temperature of something, we're talking about the average kinetic energy. Each of the individual molecules, they all have different kinetic energies. They're all bouncing around in different ways and transferring the momentum in all different ways. And so you can imagine a reality. Maybe this one has a fairly high kinetic energy. It's moving in that direction. This one has a lower kinetic energy. moving in this direction. Maybe this one has a medium kinetic energy, moving in this direction. Maybe this one has a really high kinetic energy moving in that direction. And so we've already talked about how hydrogen bonds in water between the partially negative end and the partially positive ends. That's what keeps the water together as these things move past and flow past each other. What gives the water its cohesion is these hydrogen bonds. But if all of a sudden-- remember, we're talking about the average kinetic energy-- but even if we're at room temperature, and the average kinetic energy isn't so hot, you might have individual particles, individual molecules that actually have quite a high kinetic energy and if they're in the right place, if they're near the surface and their kinetic energy is high enough to break the hydrogen bonds with neighboring water molecules, and to overcome the pressure in the atmosphere, so let's say that this is, these are just gas molecules in the atmosphere here. But it's enough to break free and none of these things bounce into it and force it back to form hydrogen bonds. This thing could actually break free and enter and become water vapor. And become in its gaseous state. And it'll be so far apart from other water molecules that it won't form hydrogen bonds anymore. So by vaporizing or by this process of evaporation, what's happening? Well if your highest kinetic energy particles or some of your highest kinetic energy particles are able to escape, what's going to happen to the average kinetic energy? Well as the highest kinetic energy things escape and those are the ones that are most likely to escape, well then your average kinetic energy is going to go down. So average kinetic energy is going to go down. Or another way of saying it, is that your temperature is going to go down. Your temperature is going to go down because as these molecules turn into water vapor, they're going to be the highest kinetic energy, energy is transferred to them, and then they escape. And so what's left over is going to have a lower average kinetic energy. And you're saying, "Well, how does that "actually cool down my hand?" Well, your hand is made up of molecules as well. So let's say this is the surface of your hand, those are the molecules, they have some average kinetic energy, they are kind of vibrating in place, especially if we're talking about they're... they're a solid. And so maybe I'll draw the more, you know, they're vibrating like this, they're bonded to each other in some way. I won't go into the details of what types of molecules these are, but then if you have your water molecules here, water molecules that are sitting on the surface, and I'm drawing this is kind of a cross-section. Let me draw the water molecules. I'll draw them as blue molecules. So this is an H2O right over here. H2O. This is an H2O. And this is an H2O. And they have some hydrogen bonding, so there is some hydrogen bonding going on. Well, as the high kinetic energy water molecules escape, I'll say this one right over here escapes, and so the average kinetic energy of what's left over is lower, so then the temperature has gone down, and now your body molecules, the ones that are all warmed up, and because of whatever's going on inside of your body, well, those can now bump into, they can vibrate and bump into these water molecules and increase their kinetic energy more than the ones that have the most kinetic energy. Those might escape again. And so it's a--one way of thinking about it is that all that heat is being used to allow these individual water molecules to escape in order to vaporize. And so that heat is leaving your body, so it allows you to cool down. Cooling down happens by heat actually leaving. So that's how evaporative... I wrote evaporative cool... That's how evaporative cooling... That's how evaporative cooling actually works.