[Physics] why does gravitational force bring the clouds down?

atmospheric sciencemeteorologynewtonian-gravity

Possible Duplicate:
The Density of Clouds

according to definition of cloud :

A visible mass of condensed water vapor floating in the atmosphere, typically high above the ground

as there's an enormous amount of gravitational force on earth why can't the cloud particles cant get attracted towards earth ,

my general question is if we threw an object which weighs even 1milligram to ground it gets attracted and falls down on earth,

As per the gravity definition:

an attractive force that affects and is produced by all mass and other forms of energy as well as pressure and stress

so why can't the cloud's particle can't get attracted by gravitational force as the cloud is an form when they have tons of water particles in them?

Best Answer

I wasn't going to answer, since this is a duplicate, but I saw these clouds on the way to work and since they are relevant for the question I thought I'd post them.

Clouds

Look closely at the clouds and you'll see their bottoms are flat. That's because they are being shaped by air currents (thermals) rising from below the clouds. The average density of a cloud is only a tiny bit greater than the density of dry air, so although in theory a cloud would sink in completely still air, in practice the motion of clouds is completely controlled by air currents. In the case of these clouds the rising air currents completely outweigh any tendancy of the cloud to sink.

The flat base marks a temperature change between a lower layer of warm air and an upper layer of colder air. The rising air hits this boundary and cools, and water condenses to form the clouds. That's why you get a well defined flat base, and why all the clouds have their bases at the same level.