Hydro-Cycle Works

Water is always on the move. It falls from the sky as rain, hammers the coastline as waves, trickles through crevices 1,000 feet underground, vaporizes and sails slowly into the clouds. Even water buried under thousands of pounds of ice in the polar icecaps is on the move - its movement is slow, sometimes taking thousands of years to budge even a few inches.

Water moves continuously through a natural system called the hydrologic cycle. Powered by the heat of the sun, all the water that falls to the ground as precipitation sooner or later makes its way back into the clouds where it eventually becomes precipitation again.

The saying goes, "what goes around comes around." In the case of water, that is certainly true.

Because all of the planet's water circulates through the hydrologic cycle, Earth is a closed system. In effect, the same water is here as was here when Earth was formed.

In this activity, your students will build themselves a model of the hydrologic cycle out of two-liter soda bottles and see for themselves the process Earth uses to recycle its water supply.

Learning Goal

To use household items to build a model of the hydrologic cycle.

Subject

Science

Sunshine State Standards

Science: Processes that Shape the Earth, SC.D.1.3, SC.D.2.3; How Living Things Interact with Their Environment, SC.G.1.3

Materials

• three empty plastic 2-liter soda bottles
• three plastic bottle caps
• two feet of heavy cotton string (wick)
• hair dryer
• soil
• water
• ice
• tape
• plant seeds (Chinese cabbage, turnip, etc.) food coloring
• tools for converting the bottles into the model:
• wax pencil, scissors, an instrument
• to poke holes in the tops of the plastic bottle caps,
• razor in a safety holder

Activity (see diagrams below)

1. Gather the materials and tools you will need.

2. Use a hair dryer on the lowest heat setting to soften the glue on the soda bottle labels so that you may remove them. Mark the bottles A, B and C to tell them apart. Cut each bottle as shown in diagram on the back of this page.

3. Poke a hole in the bottle cap on B. Insert a string/wick loop so that roughly 3 inches hang down from the cap. Place a cap with no hole on C. Tie roughly seven inches of string around the neck of C, so that it hangs down about 3 inches. See diagram for examples.

4. Assemble bottles as in diagram: C fits into B, and B fits into A. Thoroughly wet both wicks. This will bring a constant source of water from a reservoir to the plant roots. Add roughly a pint (16 oz.) of water to A. This reservoir supplies water to the model's cycle. Fill B with enough pre-moistened soil to cover the top of the string loop. The string should not be pressed against the side of the bottle.

5. Plant two or three seeds of a fast-growing plant, such as Chinese cabbage or turnip, in soil inside the well of B. (Remove C from the other bottles when not performing a demonstration, so that air circulates, and the seeds can sprout and grow.)

6. Place a plastic bottle cap on top of the soil in center of B, so that the wick from C drops into it. The bottle cap represents a water body and will collect water when the model "rains."

7. Fill Bottle C with ice water. Tape the seams between bottles to seal them. Observe the bottle cap after a few hours. The model's condensation should have filled the cap with water.8. Repeat the experiment, but his time add a drop of food coloring to the bottle cap before you begin. When the rain fills the cap, the food coloring will have tainted the water. Explain that this is how pollution can contaminate water bodies.

Discussion

1. What are signs of the hydrologic cycle in the real world? (Evaporation, precipitation) How does the model reflect what happens in the hydrologic cycle? (Water evaporates, and then forms rain.)

2. How does the model demonstrate each of the concepts detailed in the vocabulary listed below?

3. What are potential sources of pollution to water bodies? (motor oil, fertilizer, pesticides, etc.)

Vocabulary

• Closed system: A process contained entirely within itself.
• Condensation: The process of changing from a vapor to a liquid; a liquid obtained by the coming together of a gas or vapor.
• Evaporation: A process in which water transforms into vapor or invisible minute particles.
• Pollution: The contamination of a natural resource from the discharge of a harmful substance.
• Precipitation: Condensed water vapor that falls to Earth as rain, snow or hail.
• Transpiration: A process by which water is released to the air from plants.