DrW wrote:In a discussion of the damage that would be caused by the Flood of Noah (an often discussed topic at MDD) thesometimesaint, who If I recall correctly has claimed a science background in the past, stated the following:
"Plus add in the FACT that water vapor has weight. Suspending that much water in the air would crush all life. "
This is a patently ridiculous statement.
The ideal gas law, PV=nRT, is taught in high school science classes (or at least it was when I was in high school). One consequence of this simple equation is that lower molecular weight gases serve to reduce the density of a gas mixture at a given temperature and pressure.
Nitrogen gas (N2) with a molecular weight of 28 makes up about 78% of the atmosphere.
Oxygen gas (O2) with a molecular weight of 32, makes up most of the rest (about 20%).
Water vapor (H2O) only has a molecular weight of 18, so as the amount of water vapor increases in the atmosphere, the less dense the air becomes at a given temperature and pressure.
.......
Apologists who don't understand this simple principle should not be debating the fine points of the Flood with those who do.
Why do you get to suppose that the pressure would be the same? (See my last sentence below)
Well, more importantly, I think you may have approached this from the wrong angle.
The point was not about density, it was about weight.
To get that you will have to multiply by volume. The volume will have changed unless one can argue otherwise.
Let us approach this by making a couple simplifications to begin -the second one is the one we will have to backpeddle on in a moment.
First, lets talk about mass instead of weight since I don't want to assume that they will be proportional quite yet. This is because w=mg only holds precisely near the surface of the earth otherwise we nead to use Newton's full law F=GmM/R^2 and since I don't yet know the resulting volume of the atmosphere and I am about to pretend that none of it will escape into space I don't know how thick the atmosphere will be and so on).
Second, as mentioned above I am going to ignore the question of how much of the resulting vapor laden mixture will disapate into space.
Now, if we could get the volume we would take it and multiply by density which is less as you say (if temp and vol haven't changed as they might).
But the volume could be huge.
However, we don't need that at all. The fact is, the new mass will be a simple sum of the mass of the water added to the mass that was already in the atmosphere.
That means of course, the mass of the new atmosphere will be much higher even if the density is lower (which just proves the increase in volume would be dramatic and in fact, we could calculate it).
To the extent that mass is proportional to weight, we will have more weight (under my assumptions).
But, if the volume turns out to be too high, there is no immediately obvious reason to suppose that the earth can hold on to it. In fact, it seems unlikely so my assumption is very questionable. This latter issue also depends on temperature since whether molecules in the upper atmosphere have an average translational velocity higher than their escape velocity is a question of temperature. If the atmosphere is very very cold more can remain bound to the earth. Lots of factor could affect this.
But this is then one more reason your analysis has to be better.
As for pressure, that is not constant as a function of height. As for pressure at the surface, this is actually due to the weight of a column of area above a unit area. So, without a much better analysis I don't think we can get the answer to the question of whether the weight would be higher or lower.
Finally, if the weight isn't the same, the pressure won't be the same (the surface area of the earth will not have changed and from this it is easy to see that change in weight just gives change in pressure rather directly).
when believers want to give their claims more weight, they dress these claims up in scientific terms. When believers want to belittle atheism or secular humanism, they call it a "religion". -Beastie
yesterday's Mormon doctrine is today's Mormon folklore.-Buffalo