雨(rain)是从云中降落的水滴,陆地和海洋表面的水蒸发变成水蒸气,水蒸气上升到一定高度后遇冷变成小水滴,这些小水滴组成了云,它们在云里互相碰撞,合并成大水滴,当它大到空气托不住的时候,就从云中落了下来,形成了雨.
另附英文：
Rain is liquid precipitation,as opposed to other kinds of precipitation such as snow,hail and sleet.Rain requires the presence of a thick layer of the atmosphere to have temperatures above the melting point of water near and above the Earth's surface.On Earth,it is the condensation of atmospheric water vapor into drops of water heavy enough to fall,often making it to the surface.Two processes,possibly acting together,can lead to air becoming saturated leading to rainfall:cooling the air or adding water vapour to the air.Virga is precipitation that begins falling to the earth but evaporates before reaching the surface; it is one of the ways air can become saturated.Precipitation forms via collision with other rain drops or ice crystals within a cloud.Rain drops range in size from oblate,pancake-like shapes for larger drops,to small spheres for smaller drops.