Basically title, you always hear “windchill only affects humans” but we use fans to cool things all the time?
In: Physics
It ultimately affects objects the same as humans. It just happens that humans are wet, warm objects.
A wet object loses heat by evaporating water to dryer surrounding air. This forms a layer of moist air, that slows down evaporation. The moisture moves away slowly through the air, wind instead just replaces the moist air.
A warm object loses heat to cooler air simply by heat flowing from hot to cold naturally. This forms a layer of somewhat warmer air, slowing the cooling, with the heat moving away to cooler air slowly. Air, that does not move, is particularly slow at this. Wind speeds it up, by replacing the heated air by cooler air. Additionally, hot air is less dense than cold air, so the heat transfer is causing some amount of “wind” by itself. Hence why we insulate buildings and clothing with material, that traps a lot of air, and why even perfectly air-tight windows can cause some “draft” when it is cold outside.
Both effects work also the other way around. Hotter-than-object air heats the object, and if water can condense from wet air to a dry object, the condensation heats the object. Wind helps to replenish heat and humidity in those cases.
So “wind chill” is really just wind speeding up what already happens, if the object happens to be warm and moist and whether the human body counts as warm and moist depends on the weather conditions.
Also, the human body maintains its “wet and warm” state by eating and drinking. Using energy from the food produces waste heat. Humans in particular also sweat as a way of actively making the *surface* wet for the sake of cooling.
By contrast, a typical inert object will over time adjust its wetness and temperature to the air. Then, and only then, wind will not affect it. Temperature and humidity change over the day, but slowly, so the effect will never be *much*.
Unless there is a sudden change, such as taking food out of the pot. Now you have a hot, wet object, that you can cool with wind.
Latest Answers