Cloud weight weasling.

[Irishman]

TBone2 said:

Anybody notice that Dave the Ph.D overreached a bit when he mentioned the concept of a skydiver crashing into “the AstroTurf” at 120 mph?

Reread that exchange again. I admit that it is confusing, but it wasn’t Dave who made the remark about the skydiver and the AstroTurf. It was “TM”, the Teeming Millions. In other words, Cecil inserted into is exchange with Dave some remarks by the Teeming Millions so as to clarify the technical points of the discussion.

King_Al said:

so what r you guys up too

Cecil wrote his response to the question, which began with the disclaimer that the questioner was incorrect, and in fact a cloud does weigh more (and also mass more) than a 747. However, to make the column interesting, he took the losing side and tried to “weasel” the answer so JMG could find a way to not lose. That’s why Cecil explained all the comments about water vapor, density of the cloud, etc. He threw in the buoyancy of the cloud to give JMG an out.

Then PhD Dave wanted to argue that Cecil’s weaseling was inappropriate. Cecil argued with him why his weaseling was okay - even though admittedly it was weaseling. And then the conversation got technical, and the Teeming Millions got lost.

rhinobird felt Cecil was not justified in weaseling. But Cecil admitted weaseling, so rhinobird’s complaint ends up just being a statement of opinion.

The rest of us began a discussion of how clouds work, how the heavy water stays suspended in the light air. That brings up air currents, humidity levels, evaporated water vs. condensated water, etc.

We all agree that clouds have weight. The weaseling is whether you include in “weight” the other forces such as buoyancy. That should be something of a slightly different term, such as “effective weight”, i.e. what you would read on a scale. “Effective weight” would take into account things like the buoyancy force, or the centripetal acceleration of the Earth (variation from poles to equator).

I’ll say that the individual cloud particles are continuously falling slowly, and their floating is caused by the change of temprature and warmer upgoing winds. Cause if we think of a cloud in a closed box it would fall to the ground, So therefore must be affected alot by their surroundings

Yes, a cloud is not just condensed water, but the air that it is entrapped in. Thus “surroundings” are a part of the picture, and trying to put the cloud in a box does change the cloud. A bit of the QM Heisenberg principle kind of effect. [Note: That’s a metaphor.]

By the way, we can respect if you aren’t fluent in English and try to make allowances, but it does help if you at least attempt to follow the conventions of the language. There’s a reason English used capitalization and punctuation.

[Arnold_Winkelried]

“used capitalization and punctuation”?

There’s also a reason why English has a present tense.

[King_Al]

Me and a buddy have been talking about air in space,
And our talk is alot like the cloud talk here.
It goes something like this…
If you take a long pipe with a opening in one end and closed in the other, And put the pipe with the open end about 10 feet over earth, And we then imagine that the other end grows out into space.
what would happen?

1. (My guess)
   The air will stay in the tube, And let its weight will be on the sides of the tube. Because gravity pulls the air down and therefore, Create a suck in the top of the pipe from the decompressing of the highest levels of air, Will at some point stop the air from being pulled further down by gravity.

The air is kept at earth by gravity, And when the air in the pipe gets time to settle, It will fall to earth and because of the emptyness of space.
It will not need any matter to replace it so it would just keep falling and leave the tube empty like space.

and because he is one of the persons i listen too
i can’t deside, but my guess will be nr.1

[SysRq2000]

Hi everybody im that buddy king_al mentioned in his last post. Here’s an illustration of what he ment to say in his last post.

http://212.242.221.105/AirPressVsGrav.jpg

King Al suggests that if you fill his tube with air, so the pressure would be the same as the pressure at ground level, the pressure only would be a little different from the top of the tube to the bottom of the tube. He also believes that this pressure doesn’t need any help to be uphold. For this to be true you’ll have to ignore the influence of gravity! I suggest that that because of gravity the pressure will be the same as the pressure outside the tube.
Now wht do you guys think?

[Irishman]

Thanks, Arnold. That is unfortunately a frequent typo I make, especially embarrassing because of its placement. I guess that’s Guadere’s Law in action.

[Irishman]

I probably didn’t spell that right, either.

[Lemur866]

In the example, the air in the pipe will be pretty much the same as the air outside the pipe. The air in the pipe will not “leak out” the bottom and be replaced by vacuum. We can see an analgous situation by placing a straw in water. The water doesn’t drain out of the straw to be replaced by air because to do so it would have to lift the rest of the water up.

[Irishman]

King_Al and SysRq2000, what you are describing has a name - it’s called a chimney.

If you run a hollow tube straight up (and ignore the stresses in the tube’s materials that would cause it to fail ), the air inside the tube will behave just like the air outside the tube. The air pressure at the bottom inside the tube matches the outside, and the same thing at the top. The pressure difference from top to bottom of the tube matches the weight of the air, just like without the tube.

However, suppose you add a heat source under the tube. You then have warm air, which is buoyant, and starts to flow up the tube. This draws in more air from the bottom of the tube, and will begin an air flow through the chimney and out the top. I’m not sure if the height of the chimney will affect the ability to flow air - weight vs convection.

I tried to find some online descriptions, without much success. There’s a little description at this site, which is mostly trying to talk about chimney placement inside vs. outside the house.
http://www.woodheat.org/chimneys/evilchim.htm

See also http://www.ae.iastate.edu/natural_ventilation.htm .

I did run across one ingenious use of natural convection that does not require a fire for a heat source. It is a solar chimney. The idea is to capture solar energy as the heat source.
http://www.me.ufl.edu/SOLAR/chimney.html
Solar Chimney article

Hope that explains things.

[Loren_Pechtel]

*Originally posted by King_Al *
Me and a buddy have been talking about air in space,
And our talk is alot like the cloud talk here.
It goes something like this…
If you take a long pipe with a opening in one end and closed in the other, And put the pipe with the open end about 10 feet over earth, And we then imagine that the other end grows out into space.
what would happen?

 My boss has joked about making a huge vaccuum cleaner that way.

1. (My guess)
The air will stay in the tube, And let its weight will be on the sides of the tube. Because gravity pulls the air down and therefore, Create a suck in the top of the pipe from the decompressing of the highest levels of air, Will at some point stop the air from being pulled further down by gravity.

 Correct, the air stays in. Simple experiment to show this--take a straw and stick it in a glass of water. Note that the water doesn't rise. The pressure at the bottom of the straw is clearly higher than the pressure at the top, but it doesn't force the water up because it's exactly balanced by the mass of stuff in the tube. (Note that you might see a slight change in the water level due to surface tension effects. This can be gotten around by using a sufficiently large tube.)