Clouds and Rain Quiz
How a cloud forms
The Sun warms seas, lakes and plants, and water evaporates into invisible water vapor. Warm, moist air rises, and as it rises it cools.
Cool air can't hold as much vapor, so some of it condenses into tiny droplets. They need something to form on: specks of dust, salt from the sea or smoke, called condensation nuclei.
Billions of these droplets, each far too small to fall, make up a cloud. High up, where it's very cold, clouds are made of tiny ice crystals instead.
Kinds of clouds
Clouds are named mostly by shape and height. Cumulus clouds are the puffy, cotton-ball clouds of fair weather. Stratus clouds are flat gray sheets that cover the sky, and fog is really a stratus cloud at ground level.
Cirrus clouds are thin, wispy streaks very high up, made of ice crystals. They can be a sign that the weather is about to change.
Cumulonimbus clouds are the giants: towering storm clouds that can reach more than 10 km high and bring thunder, lightning, heavy rain and hail. 'Nimbus' means rain cloud.
From droplets to rain
Cloud droplets are so small that it takes about a million of them to make one raindrop. Inside a cloud they bump into each other and join, growing until they're heavy enough to fall.
In many clouds, rain actually starts as snow. Ice crystals grow by stealing vapor from the droplets around them, then melt into rain as they fall into warmer air.
Raindrops aren't really teardrop-shaped. Small ones are round, and bigger ones are flattened on the bottom, like a bun, by the air they fall through.