Why are humidity and clouds different? Why is one invisible while the other isn’t? And why would humidity not clump together like clouds do?
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>Why are humidity and clouds different? Why is one invisible while the other isn’t?
* Humidity is gaseous water mixed in with the air. So like individual water molecules, in the gas phase.
* Clouds are (tiny) droplets of liquid water suspended in the air. Each tiny droplet has millions+ of molecules of water in liquid phase. That’s why it’s opaque, it’s not gas phase water any more. The tiny drops scatter light so you can’t see through it like normal liquid water either.
>And why would humidity not clump together
You’re right, water loves sticking together and forming droplets. But at any given temperature, there is enough heat/ thermal energy to keep a certain amount of water evaporated in the gas phase (as humidity) too. The warmer the air, the more humidity can be kept in gas phase before his clumping together into droplets begins. For a given amount of humidity, the temperature where the air gets saturated and starts condensing water is called the *dew point*. If the temperature falls below this point, there isn’t enough heat to keep the water all evaporated and it DOES start clumping together into droplets.
Humidity needs nucleation sites to accumulate enough to be visible. Essentially, little bits of dust that the humidity can condense on to form large enough droplets to scatter light, but still small enough to float.
Think about humidity as how much water vapors are in the air.
An individual water vapor is essentially invisible but if you get enough of them together you can see them, esp if you change the temperature around the group. Think of your warm breath on a cold day or the steam of a boiling kettle.
Fog is a larger version of the same thing. It’s usually seen in the morning when the coldest part of the night has packed the vapors together but the warm sun is trying to spread them apart.
Fog is just a cloud sitting on the ground.
Just like if you look at your straw in a cup of water it looks like it’s in a different spot, small water vapors do the same thing. So if you have enough together in a cloud, all the water vapor makes the light randomly change directions enough times that it looks opaque.
The wind blows the vapors into groups the same way snow drifts get blown into big piles. When enough vapors get together they form rain and fall from the sky.
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