Logan Shaw wrote:
Ether Jones wrote:
So for example one cubic foot of dry air at 90 degrees Fahrenheit and
one atmosphere pressure is HEAVIER than one cubic foot of humid air at
the same temperature and pressure.

The reason is simple: air is mostly nitrogen. Nitrogen occurs
naturally as a diatomic molecule, N2. Water is H2O. Use a periodic
table to figure the molecular weights of the nitrogen molecule and the
water molecule. You will see that the water molecule is much lighter
than the nitrogen molecule.

It might also help in explaining to point out that, at a given
temperature and pressure, a given volume of gas contains the same
number of molecules no matter what those molecules are. This isn't
exactly the most intuitive thing: after all, it's not how solids
behave.

- Logan
OK, OK, Its not weight we feel.

Still air with high humidity prevents our skin from effectively
dissipating heat thru evaporation of sweat. The brain interprets this
as weight, somewhat akin to the feeling of suffocation, but very very mild.