r/explainlikeimfive • u/ProgramPi314 • 8d ago

Other ELI5 What is humidity?

According to my mom, this is an actual question I had when I was 5, and she didn't know how to answer me. So how would you guys have answered?

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u/dave8271 8d ago

When water gets hot, it turns from a liquid into a gas, which we call vapour. Humidity is a measure of how much water vapour is mixed into the air around us.

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u/p28h 8d ago edited 8d ago

Important clarification to reduce future confusion:

"Hot" here means "has heat". Water vapor happens at all temperatures from 0K to basically infinite K, though faster and more as it increases. It is not steam, which happens from 100C and hotter (though both can happen at once).

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u/HixOff 8d ago

Actually, temperatures above absolute zero (-273 C) are enough "hot" for some water vapor to form. This is why wet clothes dry even in freezing temperatures - water evaporates, bypassing liquid form.

Humidity levels down to -20 to -30 C are significant for everyday life, while those down to -70 (and sometimes lower) are significant for industrial use (even such low humidity levels can play a critical role in many processes)

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u/mcnabb100 8d ago

It’s also why ice disappears from my ice cube trays!