Investigating the Water Cycle through Modeling

Explaining Water Particle Movement through the Hydrological Cycle

Jun 22, 2009 David R. Wetzel

Students construct two different models to investigate how a molecule of water moves throughout the transformation of states of matter called the water cycle.

Oceans lose and gain water in a never-ending process called the water, or hydrologic, cycle. The sun causes evaporation of tiny particles of moisture to rise from the surface of the ocean, along with the wind which causes molecules to lift from the surface. These invisible particles of water, called vapor, mix with air. As the air cools, vapor particles join as water droplets to form clouds.

Clouds shed water droplets as rain or snow and most of it falls directly back over the sea. However, enough falls on land to sustain life and eventually finds its way into rivers that ultimately flow back into the sea. Thus, the oceans never dry up and the water cycle continues.

Investigating the water cycle through construction of models provides students with a hands-on, minds-on approach to inquire into this never ending cycle. Through this concrete experience and use of science process skills, students develop a better understanding of this cycle. Students observe how particles of water transform from liquid form to vapor, then condense and become liquid again.

Investigation Using a Water Cycle Model

This simple model represents water evaporating from the oceans, condensing, and following back into the oceans again.

Materials: per group

• 2 Clear Plastic 1/2 Gallon or 2 Liter Containers
• Blue Food Coloring
• 1 Rock (fits through clear plastic container opening)
• Masking Tape
• Eye Dropper
• Water
• Digital Camera
• Ruler

Procedures:

1. Place rock in one clear plastic container (represents land)
2. Use the eye dropper to add enough blue food coloring to the water so that it is medium to dark blue in color.
3. Add water into container with the rock ensuring water level does not completely cover the rock.
4. Place the second plastic container on top the first container – opening to opening.
5. Tape the two plastic containers together and tightly sealed.
6. Place the model in a sunny window.
7. Make observations and take pictures with digital camera of the model for two days.

Questions for Students:

1. What happened to the water inside the containers?
2. What was the source of energy that caused water droplets to form on the inside of the containers?
3. What color were the water droplets on the side of the containers?
4. Why were the water droplets not the same color as the blue water in the bottom container?
5. What role did the rock (land) play in the changes occurring in the containers?

Expected Student Observations:

Students will observe water droplets form in the top clear plastic container. These droplets will move downward merging with other water droplets. As these larger droplets reach the bottom of the top container, the droplets will be heavy enough to fall into the bottom container as rain.

Students will also observe that the droplets are clear and not blue. This is because the blue food color molecules are too heavy to evaporate just like salt in seawater and pollutants in water.

Changing States of Matter Water Cycle Model Investigation

Like the first model, this model allows students to observe and explain water evaporating, along with changing states of matter.

Materials: per group

• 1 Large Zip Lock Baggie
• 1 Cup of Water
• Blue Food Coloring
• Eye Dropper
• Masking Tape
• 1 Thermometer
• Digital Camera
• Ruler

Procedures:

1. Pour the cup of water into the baggie.
2. Use the eye dropper to add enough blue food coloring to the water so that it is dark blue in color.
3. Seal the baggie.
4. Tape the baggie onto a sunny window, water should be at the bottom and tape must be as close to top as possible.
5. Place the bulb of the thermometer against the bottom of the baggie for three minutes and record the temperature.
6. Using the same procedure in Step 5, record the temperature of the baggie 30 minutes later.
7. Record observations and take pictures with the digital camera for two days.

Questions for Students:

1. Water happened to the water inside the baggie?
2. What was the source of energy that caused water droplets to form on the inside of the baggie?
3. What color were the water droplets on the side of the baggie?
4. Why were the water droplets not the same color as the blue water in the bottom baggie?

Questions for Students about Both Models

1. Was there a change in the level of water in the bottom plastic container or baggie?
2. How would a change in level be determined?
3. If there was a change in level, where did the water go?
4. If both the plastic containers and baggie were placed in a shady area, what would happen?
5. How would these changes be determined?

Expected Student Observations:

Same as model one investigation.

Making Connections about the Water Cycle

Students make connections between the two models by developing a presentation of findings from both investigations and placed on the class Wiki. Students include all data collected, digital camera pictures, and investigation conclusions. One required element of the presentation must be a Venn diagram for viewing the common findings from both model investigations. This presentation will help students make the critical minds-on connection necessary to better understand the cycle that water follows.

The copyright of the article Investigating the Water Cycle through Modeling in Curricula/Lesson Plans is owned by David R. Wetzel. Permission to republish Investigating the Water Cycle through Modeling in print or online must be granted by the author in writing.

Water Cycle

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