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Looking at the Sea The Water Cycle

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Going Further
Build a Model of the Water Cycle

Purpose

To identify the elements of the water cycle.

To identify the sun as the source of power for the water cycle.

Materials

  • large, zip-lock plastic baggies
  • water
  • food coloring
  • masking tape
  • thermometer (one that has a large range, like an outdoor thermometer)

Background Information

Water is one of the basic building blocks of all life. It is also one of the basic ingredients of our weather. About 71% of the Earth's surface is covered by water. It is present in oceans, rivers, lakes, the polar ice caps, clouds, rain or snow, ground water and living things such as plants and animals.

Water is always moving. Surface water, warmed by the sun, evaporates into the atmosphere. Water vapor is carried by the wind all over the globe. Eventually the water vapor cools and condenses into clouds, fog, dew or various forms of precipitation. Once on the ground the water can evaporate directly or travel as runoff into the ocean, rivers, lakes or a ground water system eventually to evaporate again. This dynamic pathway of water is called the water cycle.

ProcedureIllustration of water filled baggie taped to a window

  1. Put about a cup of water into the baggie.
  2. Add a drop or two of food coloring.
  3. Carefully seal the baggie and tape it onto a sunny window.
  4. Hold the bulb of the thermometer against the bag for three minutes and then record the temperature.
  5. Let the bag hang in the sun for a couple of hours then observe the bag again. Look for any changes in the bag. Hold the bulb of the thermometer against the bag again for three minutes. Has there been a change in temperature?

Going Further

Where did the tiny droplets of water on the side of the bag come from? Can you tell if there is any less water in the bottom of the bag? How would you find out?

Hold a piece of colored ice against the condensed water vapor in the bag. This action should cause more water vapor to condense and precipitate down the sides of the bag.

Move the bag to a location where there is no sun. How does this new situation affect the water cycle?


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