Why does wind feel so much colder when hitting wet skin?
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Because water evaporating is how water cools things down. Water absorbs energy in order to evaporate. Wind blowing over water makes it evaporate faster.
The moisture on your skin evaporates quickly when hit by wind, carrying heat away from your body.
Evaporation is an endothermic process, meaning it takes energy to do so. When air is blown onto water, that water wants to evaporate, especially if that air is relatively dry and has the space for the water molecules. So when the water does evaporate it pulls energy from its surroundings to make the state change. There’s that, and water is a much better conductor of heat than air, so if that water in your skin is cold (perhaps because some of it is evaporating and sapping it of its heat energy) it will feel extra cold because water is just good at conducting heat from your body.
Ok, so there are a few things at play. The primary thing to understand is how evaporating water cools you down. Water is made up of molecules. As long as they have some energy (they are not at absolute zero) the molecules jiggle around a bit. When in a liquid form, they jiggle a bit, but not enough to break away from the rest of the liquid. Water tends to stick to itself which is why it forms beads/drops. If they get enough energy to leave the other molecules and wander further away, that’s the gas phase or steam. Clearly the molecules will jiggle more because they’re warmer, but they also jiggle a lot more because they’re less confined by other nearby water molecules. That extra energy of jiggling tends to come from you. It saps your body heat to make the phase change, cooling you down.
The next thing to realize is that the rate at which water evaporates depends on a few things. Heat is a big factor, but the humidity also makes a difference. Humidity is given as a percent because it measures how much water the air can hold in gas form. Basically, the more water is already in the air, the harder it is to put more in. So it evaporates more slowly.
Essentially, the water that evaporates quickly raises the humidity near your body, but that evaporated water is slow to disperse to the rest of the air. A breeze can move that humid air away from you, replacing it with dryer air that has more room to hold evaporated water. The rate of evaporation increases, and that means the rate at which energy is drained from you also increases. Cooling you down.
One interesting fact that’s closely related but not exactly part of the answer to your question: we don’t really feel temperature. When something feels hot, it actually means it is transferring energy to you faster. Cold things are pulling energy from you faster. We actually sense the rate of transfer of thermal energy, not the amount of thermal energy. That’s why if you keep a book and a metal plate outside at the same temperature and let them acclimate together, the metal will still feel colder than the book. They’re at the same temperature, but your body is warmer than that, so you transfer heat to them. Metals are good thermal conductors which means heat transfers faster from you to the metal than to the book. If you bake fresh muffins. The muffins are hot, yes, but you can handle them long enough to take them out of the tray. The metal tray, however, will burn your have extremely quickly.
Also, tangentially, your body heat can warm up the air molecules directly and the same thing happens. The air near you heats up faster and holds on to the heat a bit so it doesn’t spread out very quickly. This slows the rate at which heat leaves your body because the difference in temperature between you and the air is smaller. But a breeze can replace that warm air with colder air. Same thing happens when you blow on hot food. It’s just providing fresh air for the hot thing to give off energy to, speeding up the transfer. But it’s nowhere near as efficient of cooling as evaporation. That energy that goes into the change from liquid to gas is massive compared to the energy it takes to heat up without changing states. Plus, water is a much better thermal conductor that air. So it will feel much colder than just wind blowing across dry skin.
Heat can help dry things out.
Conversely, things lose heat water evaporates from them.
The wind helps liquid evaporate, and hence will cool down (and help dry) wet surfaces.
When you feel cold you aren’t actually feeling the temperature of the item, you are feeling the loss of heat from the part of your body it’s touching. Same is true with wet skin. Water evaporates in the wind causing it to take some of your skin temperature with it.
that property is called evaporative cooling. substances that have a low boiling point will show this even better. for example, if you spray isopropyl alcohol on your hands and wave them around, your hand will get really cold because the ipa will evaporate very quickly.
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