To introduce the children to the Water Cycle, I read “All the Water in the World” by George Ella Lyon. The wonderful illustrations and poetic text of this book educate about the water cycle and reinforce the simple, yet profound message: water gives life.
Evaporation, Condensation, Precipitation
Water that falls from the sky today has been around since before the time of the dinosaurs. So how does the earth keep reusing the same water and what is the water cycle?
Discussion: In the water cycle, water falls to the earth as rain (precipitation). When rain falls on the ground some is used by plants and animals and some sinks into the dirt and can form underground rivers and streams. Rain also collects, into lakes, rivers and the oceans where it evaporates into vapor when the sun heats these surfaces. Plants and animals also lose water to evaporation. When the water vapor rises high enough into the sky it cools down and condenses as water droplets (clouds) and then returns to the earth as rain or snow. And the Water Cycle continues on and on….
Using a poster of the water cycle (which they helped put together) reinforced this discussion with the children.
I also did a simple demonstration that illustrated the different steps of the water cycle, and the different states of water (solid, liquid, gas).
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| I boiled water in a pot with a glass lid. As the water heated, droplets of water condensed on the lid. |
Then the children helped with two simple experiments on condensation. In one experiment each child took a turn breathing onto a mirror to see how their warm breath would condense on a cooler surface. In another experiment they helped load ice into several large cans and then felt the outside of the can as water droplets formed on the surface. I posed the question “Where does the water on the can come from?” We discussed how the water got there as the warm air hit the colder surface of the can and condensed on the outside of the can.
Properties of Water
Objective: To familiarize students with the various properties of water and to study two properties: surface tension of water, water as a solvent.
SURFACE TENSION OF WATER (water has a “skin” and water “loves” water)
Experiment #1
Materials:
4” X 4” flat piece of plastic
eyedropper for each child
small container of water
small container of dish soap w/several eyedropper in it
Procedure: Each child used an eyedropper to drop water on a sheet of plastic to observe how the drops added to each other to build one large drop. Children then introduced a small amount of dish soap to the large drop and watched the drop disperse.
Experiment#2
Materials:
one nickel & one dime / child
eyedropper for each child
small container of water
small container of dish soap w/several stoppers in it
Procedure: Each child used an eyedropper to drop water on a coin, first a nickel and then a dime. As we dropped the water on the coins we counted the drops to see which coin could hold the most drops. Children then introduced a small amount of dish soap to the large drop on each coin and watched the drop disperse.
Explanation: The water molecules are attracted to one another, but not to air molecules. So, as long as they possibly can, the water molecules will stick together rather than dispersing. This tendency of water molecules to stick together is called "surface tension." A surface tension gives water the appearance of having a "skin". This is why small droplets of water stay in a round shape rather than spreading out in all directions. Some animals, like water striders, exploit surface tension to walk on water! But surface tension can be weakened.
Questions for discussion: What do children think will happen if they keep adding drops? Why hasn’t the water spilled over the edge of the coins? What will it take to make the water spill?
WATER AS A SOLVENT
Ocean in a Bottle
Some liquids mix with water and others don’t. This is because some liquids are denser than others. For example, when oil and water are mixed together the oil always rises to the top because it is less dense than water. By placing both oil and water in a container and adding a few drops of food coloring the color will mix with only the water since it is of the same density and not mix with the oil.
What You'll Need:
Funnel
Clear soda bottle
Water
Cooking oil
Blue food coloring
Step 1: Using a funnel, pour water into a soda bottle until it is about 2/3 full.
Step 2: Using a funnel, pour oil into the same soda bottle almost to the top. The oil and water do not mix.
Step 3: Add a few drops of blue food coloring and watch as the drops of food coloring pass through the oil layer and only mix with the water.
Step 4: Put the top back on tightly, and gently tilt the bottle back and forth to create an ocean wave effect.
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