One reason our planet is so dynamic: liquid water is denser than air, but water vapor is 𝘭𝘦𝘴𝘴 dense than air. So water keeps going up and coming down.

The reason: the molecular weight of N₂ is 14+14 = 28, and for O₂ it's 16+16 = 32, but for H₂O it's just 1+1+16 = 18.

Caveat: for ideal gases at a given temperature and pressure, the density is simply proportional to the molecular weight! But water vapor is sometimes far from ideal. This chart shows the % deviation from ideality of water vapor's volume at various temperatures and pressures.

However, that chart is not very helpful for atmospheric conditions, where the pressure is 100 kPa and temperature is between 0 °C and 50 °C. A more useful chart shows the density of moist air.

So it's a bit more complicated than I made it sound, but the basic idea is right.

@johncarlosbaez listen, water doesn't respect any one, it doesn't respect any chart, it will expand when you expect it to contract, contract when you expect it to expand, it will try its best at looking extra peaceful even when pumped with several kW of power for several minutes just to burn you worse than an ethanol fire.

It is time for you to realize: water is angry, it just barely tolerates you... For now

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