Why do water molecules form clouds instead of evenly distributing with the air molecules?
In: Chemistry
When there are sufficiently few water molecules, they *do* evenly distribute and are invisible. This is what it means for air to be below its dew point. When there are too many water molecules they begin to clump together to form a bunch of larger but still very small droplets. This is a cloud or fog.
Nucleation points. A nucleation point is a particle that other molecules “clump” around. Water molecules are polar (they have a positive and a negative charge) so they stick to each other (you can think of them as a bunch of very tiny magnets). But the chance of a water molecule crashing and sticking with other molecule when in the vapor state is very low due to how far apart they are from each other so they crash with and stick to bigger molecules or particles ( dust, spores, etc)
This bigger particles act a nucleation points so water molecules stick to them and then to more water molecules which in turn atract more water molecules (bunch of tiny magnets make a bigger magnet that is stronger and atracts tiny magnets even stronger) till you end up with an agregation of vapor that has enough water molecules to be visible, thus clouds form.
Clouds are dependent on the pressure, temperature, water level and windspeed conditions of the air.
For example, a cloud can form when a patch of moist air is heated, rises, and cools as it rises so that the water condenses into droplets.
That clump of air has now moved into a place where its pressure or temperature is matching the air around it, but it’s moisture level hasn’t matched. It’s carried up moisture from below.
Why doesn’t it then simply spread out evenly? For it to spread a force has to act on it. And when such a force is present, it does spread – you can see with cumulus – and especially cumulonimbus clouds – that they are puffy like cauliflower – that’s the moist air pushing out against the air around it. It has risen to a point in the air column where it can do that.
And you can often see wind blowing streams of cloud out, especially in high altitude clouds. You can see distinctive clouds that are formed in exactly this way. Any external force that pushes it around will do exactly that.
And in other cases, where it’s not just an isolated patch of warm, moist air, but a broad area, you just get fog, or nimbostratus (like a shelf of rain cloud).
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