When a rock falls from the sky, it hits the ground much faster than a feather or leaf would...partly because of it's higher weight and density, and partly because of its shape slowing itself down. Well...the water molecules that individually comprise a cloud don't fall to the ground that quickly either (which is why they look like they're floating)...Sometimes clouds ARE falling to the ground, but only at a speed of 0.0003 feet per second (not very fast). At that speed, it would take practically forever for clouds to hit the ground (and they just don't last that long for that to happen). Moreover, when clouds form, they form by 'extra' water vapor being thrown into a saturated environment...The usual way this happens, is through upward air motion (sort of what happens when steam rises off boiled water)...Well, that upward air motion can balance any downward air motion that gravity will have on droplets, and often allow clouds to actually grow vertically to incredible heights! Sometimes that upward air motion is only present in 1/2 a cloud...where you won't see any rain underneath that part of the cloud, but in another part of the cloud twice as much! It's really neat to see when/how it all comes together.