章节大纲

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  • 水循环

    Hands cupping water flowing from a faucet into a sink.
     

    Where have these water molecules been?
    ::这些水分子到哪里去了?

    Did you ever wonder where the  water  molecules you drink came from? Were some of the molecules trapped in a  ? Flowing along the bottom of the ocean? Up high in a thundercloud? Maybe a water  molecule  that you drink today once quenched the thirst of a dinosaur. It's all entirely possible.
    ::你有没有想过你喝的水分子来自何方?一些分子是否被困在海底?在海底流淌?在雷球中高处?也许今天你喝的水分子曾经解开了恐龙的渴。这一切都是完全可能的。

    The Water Cycle
    ::水循环

    The  water cycle  ( Figure   ) is the movement of water between different  reservoirs .  On Earth, water can exist in the  atmosphere , oceans, underground, and in living things. The water cycle is powered by  energy  from the  .
    ::水循环(图)是不同水库之间的水流动。 在地球上,水存在于大气、海洋、地下和生物中。水循环由来自水的能量驱动。

    The water cycle, showing evaporation, condensation, precipitation, and surface runoff.
     
    The water cycle has no beginning or end. Water just keeps moving along.

    Water keeps cycling. The water cycle repeats over and over again. Each water molecule has probably been around for billions of years. That’s because Earth’s water is constantly recycled.
    ::水循环不断循环。 水循环反复重复。 每个水分子可能已经存在数十亿年了。 这是因为地球的水不断被回收。

    Processes in the Water Cycle
    ::水循环过程

    Water keeps changing state as it goes through the water cycle. This means that it can be a solid, liquid, or gas. How does water change state? How does it keep moving through the cycle? As seen above ( Figure   ), several processes are involved.
    ::水在水循环中不断改变状态。 这意味着水可以是固体、液体或气体。 水的变化状况如何? 水是如何在循环中不断移动的? 如上( 图 ) 所示, 涉及多个过程 。

    • Evaporation  changes liquid water to  water vapor . Energy from the Sun causes water to evaporate. Most evaporation is from the oceans because they cover so much area. The water vapor rises into the atmosphere.
      ::蒸发将液态水改变为水蒸气。太阳产生的能量导致水蒸发。大部分蒸发来自海洋,因为它们覆盖了这么多区域。水蒸发进入大气层。
    • Transpiration  is like evaporation because it changes liquid water to water vapor. In transpiration, plants release water vapor through their leaves ( Figure   ). This water vapor rises into the atmosphere.
      ::蒸发就像蒸发一样,因为它将液态水变成水蒸气。在蒸发中,植物通过叶子释放水蒸气(图)。这种水蒸气会升入大气。
    Plant roots absorbing water and releasing vapor through leaves in transpiration.
     
    Liquid water is taken up by plant roots. The plant releases water vapor into the atmosphere. This is transpiration.
    • Condensation  changes water vapor to liquid water. As air rises higher into the atmosphere, it cools. Cool air can hold less water vapor than warm air. So some of the water vapor condenses into water droplets. Water droplets may form  . Below is an example of condensation ( Figure   ).
      ::凝聚会将水蒸发变成液态水。 当空气向大气中上升时, 它会冷却。 冷空气能容纳的水蒸发量比温暖空气少。 因此有些水蒸发体会凝聚到水滴中。 水滴可能会形成。 下面是凝结的例子( 图 )。
    A glass of cold water with condensation and ice, demonstrating the condensation process.
     
    A glass filled with ice water becomes cold. It cools the air near the glass. Cooler air can hold less water so water vapor condenses onto the glass.
    •  is water that falls from clouds to Earth’s surface. Water droplets in clouds fall to Earth when they become too large to stay aloft. The water falls as  rain  if the air is warm. If the air is cold, the water may freeze and fall as  snow ,  sleet , or  hail . Most precipitation falls into the oceans. Some falls on land.
      ::水是从云层流到地球表面的水。 云层中的水滴在云体太大而不能停留在高空时会掉落到地球。 如果空气是温暖的,水会像雨一样降下。 如果空气是冷的,水会像雪、流水或冰雹一样冷却和落下。 大部分降水会降入海洋。 有些降水会落在陆地上。
    • Runoff  is precipitation that flows over the surface of the land. This water may travel to a  river ,  lake , or ocean. Runoff may pick up fertilizer and other pollutants and deliver them to a water body. In this way, runoff may pollute bodies of water.
      ::径流是指在陆地表面流动的降水,这种水可能流向河流、湖泊或海洋,径流可能收集肥料和其他污染物,并将它们输送到水体中,以这种方式,径流可能污染水体。
    • Infiltration  is the process by which water soaks into the ground. Some of the water may seep deep underground. Some may stay in the  soil , where plants can absorb it with their roots.
      ::渗入过程是水渗入地下的过程,有些水可能渗入地下深处,有些可能留在土壤中,植物可以用其根部吸收土壤。

     

     

      

    Science Friday: Forecasting the Meltdown: The Aerial Snow Observatory
    ::科学星期五:预测熔化:空中雪天文台

    75% of Southern California's water supply comes from the snowpack in the Sierra Nevada  Mountain  Range. This video by  Science  Friday explains how NASA uses specialized instrumentation in the Airborne Snow Observatory to carefully measure the water content.
    ::南加利福尼亚州75%的供水来自内华达山脉山脉的雪堆。这段由科学周五拍摄的视频解释了美国航天局如何在空降雪观测站使用专门仪器来仔细测量水含量。

     

     

     

    Summary
    ::摘要

    • The water cycle recognizes all of the reservoirs of water. It also describes the processes that carry water between the reservoirs.
      ::水循环承认所有水库,还描述了水库之间的水输送过程。
    • Water changes state by evaporation and condensation. Plants release water through their leaves by transpiration.
      ::植物通过蒸发和凝聚从叶子中释放水。
    • Water can move between reservoirs through precipitation, runoff, and infiltration.
      ::水可以通过降水、径流和渗透在水库之间流动。

    Review
    ::回顾

    1. What is transpiration?
      ::什么是蒸发?
    1. How are evaporation and condensation the same? How are they different?
      ::蒸发和凝聚如何相同?它们有什么不同?
    1. What is the role of the major reservoirs in the water cycle?
      ::主要水库在水循环中的作用是什么?