人人终身学习知识网~是各类综合知识资源信息分享,提升综合素质与提高知识技能的终身学习网络平台

 找回密码
 立即注册

QQ登录

只需一步,快速开始

微信登录

微信扫码,快速开始

[六级大学英语阅读] 六级冲刺练习阅读(129)

[复制链接]

  Precipitation

  The dictionary defines the word precipitation as a falling down , and when the meteorologist uses this word with regard to the weather he is speaking of the rain, snow, sleet, and hail which fall down to earth from the atmosphere. All of these examples of precipitation have something in common. In every case what falls to the earth is water in one form or another.

  Evaporation. In order to understand why precipitation occurs and to appreciate some of the similarities and differences in the various types of precipitation, we must first find out how water gets into the atmosphere. This will also help us to understand some of the other weather elements like dew and frost, and clouds and fog.

  Of course you have seen water disappear from a wet street or from the surface of a fish tank. We call this disappearance evaporation. Why does water evaporate and where does the water go?

  Scientists know that water, like all other substances in the universe, is composed of countless billions of tiny particles known as molecules. The molecules of water are so small they cannot be seen with even the most powerful electron microscopes ever devised. There is ample proof of their existence, however, and we also know that these molecules are constantly darting about and colliding.

  Now, consider the water in an aquarium. Throughout the tank, water molecules are speeding about and bumping into each other, The constant collisions prevent the tiny particles from getting very far. At the surface of the tank, however, many molecules can escape freely into the air. This is the process of evaporation and it is through this process that water is constantly entering the atmosphere. The molecules of water are, of course, too small to be seen, and so we speak of trie water in the air as an invisible vapor. When the temperature increases, the speed at which the molecules move also increases. Faster-moving molecules escape more rapidly and evaporation is speeded up when it is warm.

回复

使用道具 举报

小黑屋/人人终身学习知识网~是各类综合知识资源信息分享,提升综合素质与提高知识技能的终身学习网络平台

Powered by 5wangxiao

© 2007-2021 5wangxiao.Com Inc.

快速回复 返回顶部 返回列表