Raindrop formation

Raindrops are formed when water inside a cloud condenses onto a nucleus. Other water molecules are attracted to the nucleus and the to each other, and they also condense. A nucleus can be a particle of ice, dust or pollution. As the mass of the droplet increases, the raindrop becomes heavier and may start to fall toward the earth. Most raindrops evaporate back into the air before hitting the ground. In order for a raindrop to hold together and become "rain," the droplet has to be between 0.5 and 5 mm. Some scientists think that all raindrops actually start out as ice or snow and melt on the way to the ground.