Originally Posted by
88ss
Let's see, take dry air, add water to it, and it weighs less according to you. LOOOOOOOOOOOOOOOL
No, it's according to the facts.
Dry air is 80% N2 and 20% O2 (I rounded the figures).
Both have a molecular weight higher than water vapour (28 and 32 versus 18).
All gasses have the same number of molecules per unit volume - and this includes mixtures of gasses.
So the density of a mixture of N2 and O2 and H2O is less than a mixture of just N2 and O2.