system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Lifeguard here, why does 80 degree weather feel hot but 80 degree water feel cold?
gpt
Physics. You body generates a certain amount of heat, and tries to keep your temperature constant at 98.6 F. Air is not very dense, and thus is not all that efficient at taking away your extra heat. Your body is generating heat faster than it is being lost to the air, so your compensatory mechanisms (sweat, lowering energy level, etc.) kick in. Water is extremely dense and has an extremely high heat capacity, so it is extremely efficient at taking away extra heat. That's why we use it in things like radiators and other cooling systems.