how many pounds to clouds weigh?

Question

seriously how many ponds do they weigh......
and

how do they float in the air (sky) like that

Answer 1

Clouds are in a constant state of evaporating and recondensing. Clouds are actually small drops of condensed water. You can see this for yourself if you ever go through fog during the daytime.

The droplets are small enough that their terminal velocity is small, but nevertheless the droplets are constantly settling towards the earth. Water droplets are denser than air and average amongst many of them tend to be falling, though local winds will dominate over the small terminal velocity.


Complicating things, water vapor (note that visible steam is NOT water vapor...it is droplets of water that have condensed out of water vapor that is in the same area) is less dense than air, simply because the molecular mass of water is about 2/3 that of air, so the vapor that is often associated with the droplets in cloudswill tend to be buoyant creating an updraft. I suspect that when this updraft is larger or the same as the terminal velocity of the droplets, there is no rain. One of my sources says buoyancy from rising warm surface air dominates.

As they fall they can evaporate (except when the density is high enough that they start sticking together to form bigger droplets with higher terminal velocity and don't have time to evaportate again. This is called rain.) More droplets form higher up, and the cycle continues. When the replacement rate (depends mostly on relative humidity near the cloud boundaries) is slower than the destruction rate the cloud disappears. When it is faster you get many more droplets and rain forms.


To calculate the mass you need the volume of the whole cloud, the number density of droplets (droplets/ cc for instance) and their rough size.

Example...a large cumulo-nimbus cloud can be 20 km tall (2000 meters). Assuming it is as wide as it is tall, it will have a volume of approximately 6x10^12 cubic meters (6 trillion cubic *meters*). Droplet sizes tend to be around 10 microns and you will have about 10^10 of them per cubic meter. Multiply it all out and you end up with 31 million metric tons of water.

Answer 2

A lot. As usual, Wikipedia has answers:

http://en.wikipedia.org/wiki/Humidity

Let's say a cloud contains 10g of water per cubic meter and has a volume of 1km^3, it will contain 0.01kg/m^3*(1000m)^3 = 10^7kg = 10,000 tons of water.

I don't think anybody would want that to rain down on their back yard...

Including the air, it is a lot more, of course... because 1m^3 of air weighs about 1.4kg (or so). So now we are talking over a million tons...

Why do clouds float? Because the density of the cloud is lower than the density of air...

:-)

Answer 3

Well, the problem you have dropped onto us for solution is just a little hard to handle from where I sit. The particular cloud that you wish for me to weigh or measure the weight of...
CAN YOU PLEASE POINT IT OUT TO ME? I will also need the height, length and width of it to deliver an accurate answer to you. The actual weight of clouds actually varies somewhat with color also. So in addition to the measurements and actual identification of the particular cloud you want weighed, I will also need to know if it is:

a.) White and fluffy.
b.) White and Flat.
c.) Gray
d.) Dark Gray
e.) Black