system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why does air from a normal fan FEEL colder when it hits your face, even if the fan doesn’t change the temperature of it?
gpt
The air that is hitting your face is not colder (well, it’s probably colder than your body temperature), but there are two reasons it feels colder. First, if you’re just sitting still and the air around you isn’t moving, the air closest to your skin gets heated up by your body and doesn’t go anywhere. But if the air around you is constantly moving, that warmer air next to your skin will be replaced by cooler air. Second, moisture on your skin evaporates, and if air is moving over your skin, it evaporates faster - and the evaporation itself does cause cooling (this is why we sweat, because it cools us off). In fact there are even machines called evaporative coolers or swamp coolers which can cool the air in a room significantly just by moving air over a damp surface (but these only work in places where the air isn’t very humid).