what makes it rain? rain falls ｆrom

what makes it rain? rain falls ｆrom clouds for the same reason anything falls to earth. the earth’s gravity pullsit. but every cloud is made of water droplets ｏr ice crystals.why doesn’t rain ｏr snow fall constantly ｆrom all clouds? the droplets ｏr ice crystals in clouds are exceedingly small. the effect of gravity on them is minute. air currents move ａnd lift droplets so that the net downward displacement is zero, even though the droplets are inconstant motion.droplets ａnd ice crystals behave somewhat like dust in the air made visible in a shaft of sunlight. to the casual observer,dust seems to act in a totally random fashion, moving about chaotically（混乱地）without fixed direction. but in fact dust particles are much larger than water droplets ａnd they finally fall. the cloud droplet of average size is only 1/5,000 inch in diameter.it is so small that it would take sixteen hours to fall half a mile in perfectly still air, ａnd it does not fall out of moving air at all. only when the droplet grows to a diameter of 1/125 inch ｏr larger can it fall ｆrom the cloud. the average raindrop contains a million times as much water as a tiny cloud droplet. the growth of a cloud droplet to a size large enough to fall out is the cause of rain ａnd other fｏrms of precipitation（降水）. this impｏrtant growth process is called“coalescence”.