[Phys-L] Re: A "simple" physics problem?

[Brian Whatcott <betwys1@SBCGLOBAL.NET>]

>  Vickie Frohne wrote:
>
> > BTW, this question is tied into some environmental issues.
> > Any rise in the ocean levels due to global warming will be
> > due to ice that's currently on land (ice sheets in Greenland
> > or Antarctica). Melting sea ice (i.e. the north polar ice
> > cap)will not contribute to the rise in sea level because
> > floating sea ice is already displacing ocean water.
>
> That assumes there is no heavier-than-water object resting on (or in)
> the ice?
>
>  Herbert H Gottlieb wrote:
>
> > Please don't forget that as the sea water becomes warmer
> > it heats the air above the water. The warmer air can hold
> > much more moisture making the sea level even lower by an
> > rch or two.
>
> And so global warming, by warming the water, will lead to additional
> evaporational cooling, which will cool the air back down to normal?
>
>  Brian Whatcott wrote:
>
> > I may be missing something.  Moist air is less dense:
> > its columnar weight is less than dry air, so a water level
> > beneath it would rise.

Bob Cohen wrote

> Assuming the pressure is the same.  As you point out, the surface
> air pressure is closely related to the total columnar mass.
> Evaporating water into the column will *increase* the air pressure,
> won't it?
>
> ____________________________________________________
> Robert Cohen; 570-422-3428; www.esu.edu/~bbq
> East Stroudsburg University; E. Stroudsburg, PA 18301


I used the idea of a surface air pressure being calculable from
  the gravitational pull on the mass of the column of air out to
vacuum - which I called its weight.

I asserted that water vapor is lighter than dry air, which is true -
other things equal - so I implied that moist air tends to go with
lower air pressure, and hence  higher water level in the region.

So I say again, adding humidity tends to decrease air pressure.
But I will listen to reasons why you are right!
:-)


Brian Whatcott    Altus OK    Eureka!
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