BACKGROUND:

Students by the 6th grade should be familiar with the mechanism of the water cycle. They might not realize the significance of water to enable life to exist on Earth.  The following is a summary of the importance of water to life. 

1. Water remains a liquid over a very wide temperature range, namely, a range of 100C°  between freezing and vaporization.   This spans the temperatures of most parts of the Earth where life can occur. 
      
2. Water has a very high specific heat, which means that it can absorb or lose much heat before its temperature changes.  This is important in maintaining body heat in mammals, such as ourselves.
     
3. Water has a high latent heat of vaporization.  For this reason, water evaporates slowly from ponds and lakes, where many life forms are dependent on it. 
      
4. Water is less dense in its solid state than in its liquid state, so that ice floats instead  of sinking.  This property permits life to develop in polar regions and subpolar regions where ice floats and allows life to continue living below the surface.  If ice were heavier than water, it would sink, and more ice would form on top of it.  As a result, all life in the waters would be trapped in the ice in the many areas of the world where it gets cold enough to freeze water.
     
5. Water is a remarkable solvent not only for the reasons mentioned above but also for gases such as oxygen and carbon dioxide.  The oxygen must be soluble in the water phase of the living cell in order for it to be used for oxidation of food.  At the same time, another gas, carbon dioxide, must also be soluble to escape to the outside of the cell, from where it travels to the lungs to get expired.
     
6. Water exhibits surface tension.  The molecules of water on the surface of a calm and quiet pond tend to be drawn into the liquid, so that the liquid surface is taut, like a sheet of rubber drawn over the open mouth of a jar.  This tautness is called surface tension.  It can support small objects like a sewing needle.  This "skin" on the water can also cause a handicap to mayflies and caddisflies that try to emerge from their juvenile images.  It also can trap flying insects that accidentally fall into the water and are unable to fly out. 
      
7. Water exhibits viscosity.  One can observe the effects of viscosity alongside a stream or river with uniform banks.  The water along the banks is nearly still, while the current in the center may be swift.  This resistance between the layers is called viscosity.   This property allows smaller fish to live near the shore, while larger fish are able to swim efficiently in strong currents.  Viscosity is also responsible for the formation of eddies, creating turbulence that leads to good mixing of air in the water and more uniform  distribution of microscopic organisms. 

PROCEDURE:

1. The water cycle can be very simple, but the more times a student is introduced to the concepts, the more involved the cycle becomes.  The movement of water involves more than just evaporation and precipitation.  Go over the major parts of the water cycle as illustrated by the diagram below.

• evaporation - the changing of liquid to water vapor

• condensation -  the changing of water vapor to a liquid

• precipitation - forms of water vapor that are heavy enough to fall to the Earth's surface such  as rain, snow, sleet, hail, and fog

• infiltration - the process by which water seeps into the soil

• water table - the level below which the ground is saturated with water

• lake - a body of water larger than a pond and too deep in parts for rooted plants to live

• river - a natural stream of water larger than a creek and emptying into an ocean, lake, or  another river

• ocean - the bodies of salt water that cover nearly three fourths of the surface of the earth 

• groundwater - water found below the surface of the Earth

• runoff - water that flows on the surface or through the ground into streams, rivers, lakes and  oceans

• transpiration - the evaporation of water from the leaves of plants

2. Use the worksheet and have the students draw in some of the components to make the diagram easier to understandable.  You may want the students to write a paragraph on the water cycle, taking information from the worksheet.
   

3. Use the online poem of Dr. Drippy to illustrate how poems can be a fun way to learn the content of the water cycle. Students should read Dr. Drippy. This poem is based on key words from the water cycle. Challenge students to write their own poem or limerick on the water cycle.

   A poem is a composition of a verse that uses rhymes to express a subject in an artistic fashion. Students can either have it rhyming or not depending on how they us their imagination.

   You may also want to assign students to create a limerick. A limerick is kind of a humorous verse of 5 lines in which the first and second lines rhyme with the fifth line. The shorter third line rhymes with the shorter fourth line.

   You may want to pair up students, one with artistic talents and the other the writer.

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