44.WHY DON’T ALL CLOUDS PRODUCE RAIN?
Have you ever flown through clouds in an aircraft, or perhaps been high up on a mountain where the clouds swirled act about you? Then you must have gained a fairly good idea of what a cloud is: just an accumulation of mist.
As you know, there is always water vapor in the air. During the summer there is more of this vapor in the air because the temperature is higher. When there is so much water vapor in the air that just a small reduction in temperature will make the vapor condense Form tiny droplets of watery, we say the air is saturated.
43.WHY DO WE HAVE FLOODS?
For as far back as we can go in the history of man, we find records or tales, or legends, about great floods. The reason for this is that there have always been floods. In fact, primitive man deliberately settled in the valleys that were in the paths of floods because they were so fertile.
What is a flood? It’s a condition that exists when a river overflows its banks and the water spreads out elsewhere What causes a flood? the accumulation of a great deal of water in a river that comes from heavy rains, or from other streams or reservoirs that feed into the river. A river usually drains a vast area, or ‘watershed,’ and it is the heavy flow of water from anywhere in this watershed that makes a river rise and flood over its banks.
42.WHERE DOES WATER GO WHEN IT DRIES UP?
You look out on the street or road and you see water. An hour later in bright sunshine, it is gone! Or wet clothes are hung out on a line, and by the end of the day, they are dry. Where did the water go?
We say the water evaporates. But what does this mean? Evaporation is the process by which a liquid that is exposed to air gradually becomes a gas or vapor. Many liquids evaporate quite quickly, much more quickly than water. This is true of alcohol, gasoline, and ammonia. Some liquids, such as mercury, evaporate very slowly.
