天上的雲為甚麼不會掉下來？

Clouds are formed by water vapor and condensation nuclei. When hot air rises, water vapors follow. As water vapors reach a certain altitude, or to its dew point, water vapors condense around condensation nuclei such as salts and dust. As these water vapors condense, they form clouds. Clouds do not fall because it is being kept on the same atitude

During daytime, some water in the sea turns to water vapour and rises. on the sky, the water vapour turns to cloud, there are many water on the clouds, the clouds cannot take water, it for down as rain. It is some gas, it is light than the air, so it will not fall down.

因為雲是水蒸氣,是氣體,當在天上凝結成水點,空氣抵受不了,
就會下水,下水就是下雨。

雲是怎樣形成的呢?
參考:
http://www.sgjh.tc.edu.tw/Web/CLOUDS/c1-4.htm
http://www.weather.com.hk/learn/cloud.asp

夏天，地面被太陽曬得火辣辣，地面的空氣被烤熱變輕，就上升到天空中。熱空氣一邊上升，一邊漸漸冷下來，凝結成很多小水滴，就形成一塊雲。由於這種小水滴非常輕，上升中的空氣十分容易托往它，因此就浮在空中。
另外，冷空氣同熱空氣相遇時，冷空氣也把熱空托到天空，使它變成雲；有時，向前流動的濕空氣碰到山嶺、高原時，也會被迫上升，形成雲霧。

they r just gas