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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?

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please help me in providing tags for this question –  BlueBerry - vignesh4303 Aug 14 '12 at 10:28
your question is pretty much an exact duplicate of the question I've linked. It's usually a good idea to search the forum before posting. Have a read of the other post, and if anything is still unclear maybe edit your question or post a new one. –  John Rennie Aug 14 '12 at 10:42
"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?" Because the cloud is so light, this gravity between the particles of the cloud is negligibly small since it is completely accounted for by air resistance, frication etc,.. –  Dimensio1n0 Jun 6 '13 at 13:05
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marked as duplicate by John Rennie, Qmechanic, Colin K, dmckee Aug 14 '12 at 16:37

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

1 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.


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.

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It is really a shame that a google search does not list the physics forum as a search result --perhaps we need better tagging/meta-data. –  Monster Truck Aug 14 '12 at 14:03
+ Minor note about the flat bases: You don't have a layer of warm and a layer of cold. You have a more-or-less linear drop in temperature with altitude (the lapse rate), caused by various things like 1) rising air expands, thus cools, and vice-versa, 2) surface heated by sun, etc. If the rate is too steep the air is unstable & you get localized updrafts and clouds like above. If less, you get stratified clouds. If negative, you have a temp inversion, like in Los Angeles smog. –  Mike Dunlavey Jul 11 '13 at 13:30
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