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This is about a group project for our science class and we've decided to do a physical model on clouds.

We could use liquid nitrogen and hot water to demonstrate the formation of the clouds and we are aware that it doesn't form like that in the nature.

I just wanted to ask, what's the pressure required for clouds to form? I found out that it's -10o C temp. but nothing about pressure (lower than normal but don't have the exact number)

Any ideas? :( I'm starting to feel pretty desperate.

Can we use the nitrogen to decrease the temperature to -10 and then pressure, and wait for liquid water to condensate?

Any kind of answer will be appreciated. Thanks :)

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  • $\begingroup$ Wait until it's below -30°C outside and throw hot water down from the second floor ;-). $\endgroup$
    – gerrit ♦
    Oct 14, 2016 at 8:01
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    $\begingroup$ azot? Do you mean liquid nitrogen? Please edit the question, and while you're doing that, add some white space. $\endgroup$
    – Jan Doggen
    Oct 14, 2016 at 9:32

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To form a cloud, generally speaking, pressure does not play a significant factor (with the exception of the effect on temperature).

If you want to prove that to yourself, go outside when it is foggy and measure the air pressure. Fog is a cloud, and pressure likely hasn't changed as much as it does in the vertical direction.

As far a forming a cloud, it is actually relatively easy. You only need to decrease the temperature to it's dewpoint. You may want relatively dirty air, so that the solute effect makes it easy to form drops. Silver iodide would be good for this.

For reference, the Kohler curve describes the saturation needed for cloud droplets to form.

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I actually disagree that pressure isn't a significant factor. It is pressure and temperature together that determine boiling and condensation points. The atmospheric pressure on Everest is roughly 1/3 that of standard atmospheric pressure making water boil at 71C instead of at 100C. Using simple plastic containers like 2 liter bottles you can achieve around 100 psi safely which is roughly 7 times standard atm. For this reason you can create a cloud in plastic bottles using a bike pump or even just squeezing it to manipulate this principle. This link shows you how to make a cloud in a bottle with actual water http://www.wikihow.com/Make-a-Cloud-in-a-Bottle but if you want some wow factor you can use a bike pump and alcohol to form a large amount of fog or cloud like in this link http://www.abc.net.au/science/articles/2013/05/21/3759793.htm

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