1. Water Cycle Stories
In this lesson, students review the water cycle (a concept most have hopefully explored before in elementary school science) and write stories to describe the journey of a water molecule through the water cycle. They begin by labeling a drawing of the water cycle, noting the locations that water may be stored on the planet and the processes through which water travels from one location to another. They then envision several journeys as a class before writing a story to describe the journey of a water molecule through the water cycle. An optional mini-investigation to complement this lesson involves observing the transition of water through its 3 phases (ice, water, water vapor) after an ice cube is zipped into a resealable plastic bag and taped to a sunny window.
Can list the 3 phases of water and understand how heat contributes to the transition from one phase to another.
Can discuss the various locations where water is stored on Earth and the processes through which water travels from one location to another.
Can describe the water cycle.
1. Water Cycle Stories - Logistics
1-2 hours depending on the students’ previous exposure to the phases of matter and the water cycle
For water cycle discussion:
- Glass of ice water to start the discussion
- Copies of Water Cycle Stories handout
- Overhead projector (or draw a copy of the image on the board)
- Overhead transparency of Water Cycle diagram
For optional mini-investigation each student needs:
- Ziplock bag
- 1 ice cube
- 1 sample cup (the little paper cups ketchup is sometimes served in)
- several scales or balances for students to weigh their bag
- sunny window or sunny exterior wall
1. Water Cycle Stories - Background
The water cycle is at the center of many scientific topics, from watersheds (like this unit) to weather patterns to ice ages. The main idea is that almost all the water that exists on Earth today was there since the planet formed 4.6 billion years ago. However, water molecules do not stay in one place for long, at least not on a geologic time scale. The sun drives a continual process of evaporation, condensation, freezing, and melting that allows any given water molecule to travel from location to location on Earth. Thus the water cycle is the journey that water takes through its various phases (or states) – solid ice, liquid water, and gaseous water vapor – as it travels through Earth’s systems.
Water can exist in 4 phases or states – solid, liquid, gas and plasma – although plasma has little relevance to most everyday events including the water cycle. The molecules of a solid are tightly packed and bonded together so that the substance retains its shape. The molecules of a liquid are closely packed but can move relative to each other so that the substance flows. The molecules of a gas are independent of each other and move about freely in 3 dimensions. The transition from one phase to another is governed by temperature and pressure. As temperature increases and pressure decreases, a solid substance will generally transition to a liquid (it melts) and then from a liquid to a gas (it evaporates). As temperature decreases and pressure increases, a gas will generally transition to a liquid (it condenses) and then from a liquid to a solid (it freezes). It is possible for substances to transition straight from a solid to a gas in a process called sublimation. For instance, snow sometimes sublimates without turning to liquid water first. Similarly, dry ice sublimates straight to carbon dioxide gas.
With respect to the water cycle, water as a gas may travel huge distances across oceans and continents before it condenses and turns to rain or snow. Water as a liquid will flow across the Earth’s surface and percolate into the ground. Thus, water travels a lot as it undergoes phase changes. Most of this is governed by temperature as the result of the sun’s energy and less by pressure. One can therefore think of the water cycle as powered by the sun.
The water cycle is illustrated below. There are 6 major storage locations for water:
- Surface water (lakes, rivers, reservoirs, oceans, etc.) - The vast majority of Earth’s water, 97% of it, is stored in oceans.
- Atmosphere (clouds, fog, humidity, etc.)
- Precipitation (rain, snow, sleet, hail, and ice) – Water stored as precipitation in the form of snow is critical to the state of California since most Californians depend on snowmelt to provide them with fresh water throughout the dry summer months.
- Glaciers – These giant, slowly moving ice sheets form from snow that compacts and recrystalizes over time to form large ice crystals. Glaciers are more important than many realize. Approximately 75% of the Earth’s fresh water is stored as glaciers, primarily around the polar ice caps.
- Living organisms – Our bodies are 50-70% water!
From each of these storage locations, water has ways to travel to other locations. Water may:
- Evaporate –from surface water into the atmosphere
- Condense – from the atmosphere into precipitation
- Melt – from precipitation as snow to surface water or from glaciers to surface water
- Freeze – from precipitation as snow to glaciers
- Percolate – from surface water to groundwater and back again
- Transpire – from living organisms to the atmosphere
- Drink – from surface water (or sometimes groundwater) to living organisms
- Excrete – from living organisms to surface or groundwater
Previous exposure to the phases of matter and the water cycle is helpful but not necessary. If students have not learned about these topics in the past, then on day 1, do the phases of matter mini-investigation and discuss the locations where water is stored. On day 2, analyze the results of the mini-investigation and discuss the transitions between locations in the water cycle.
1. Water Cycle Stories - Getting Ready
- Make copies of the Water Cycle Stories handout for each student.
- Make overhead copy of the Water Cycle diagram.
- Fill a clear glass with ice water and leave it on a coaster at the front of the room.
- Get dice.
For optional mini-exploration:
Collect materials: Ziplock bags, ice cubes, tape, scales.
1. Water Cycle Stories - Lesson Plan
- Ask students what they predict will happen if I zip an ice cube in a Ziplock bag. In particular, what will happen to the weight of the bag as the ice turns to water and then turns to water vapor? Many students will think that the bag will weigh less after the water melts and some of it turns to water vapor.
- Have students write down their predictions on a lab notebook. I had my students draw a series of pictures with captions showing the plastic bag now, in 2 hours, and tomorrow.
- Try the experiment. Pass out bags, sample cups and ice cubes. Place the ice cube in the sample cup and then place the whole thing in the Ziplock bag. Make sure there is a good quantity of air in the bags before sealing them so that any condensation that accumulates may be observed. Make sure the bags are tightly sealed.
- Have each student measure the mass of their bag and record that measurement in their lab notebook before taping the bag to the window or wall. Make sure the sample cup is right-side-up with the ice inside. If you wish, you can use any remaining class time to introduce the locations on Earth where water is stored (Step #10 of the Water Cycle discussion lesson plan below).
- The following day, make some observations of the bags before taking them down. The ice should have melted and some condensation will have appeared on the sides of the bag and run down the sides of the bag to collect below the cup.
- Take the bags down and remove any tape. Measure the mass of the bags and compare the measurement to the previous day.
- Ask the students: Did anything surprise you? Did everything happen according to your predictions? Flow directly into the Water Cycle discussion below.
Water Cycle discussion and storytelling:
- Begin by setting the glass of ice water on the table at the front of the room. Ask the students to make observations of the glass. What is happening to the ice? What is happening on the outside of the glass? Why are these things happening?
- Allow these initial observations to transition into a discussion of phase change. Ask students what they know about how and why water can transition from ice to liquid water to water vapor. Students may or may not know about how increasing temperature translates into molecular movement – that solids are solids because the molecules are locked in place and can only vibrate while in gases the molecules are energetic and move freely.
- Invite 9 volunteers to come to the front of the room. Each student represents one molecule of water. Have them stand closely together in 3 rows of 3 students and interlock arms. They now represent water in its solid form – ice. Tell them that they are cold. They may shiver and vibrate a little but should remain bound together.
- Now tell them you have placed the glass of water in a sunny window and the molecules of water in the ice cube have begun to get energized. They can now move around but should stay together in a cluster. They have melted and become liquid water. They should naturally unlink their arms and perhaps might join hands. Allow them to “flow” around the room and use that to illustrate the fluid motion of liquids. If you wish, you can introduce the idea of hydrogen bonding and surface tension as the reasons that liquids stay together.
- Now tell them that the sun has become really warm and they are very very excited and can move about freely. The cluster of 9 will soon disperse about the room, probably colliding with desks, other students and the walls of the room. You may need to have the water molecules “freeze” temporarily in order for your explanation to be heard by the students. They have evaporated and now represent water as a gas – water vapor or steam.
- Finally, tell them that the sun has set and it is beginning to become cold. When they collide with another water molecule, they should “stick together for warmth”. Soon all the water molecules will form a liquid again. They have now condensed back onto a liquid. You may take things all the way back to the beginning again and tell the molecules to freeze solid by linking arms once again.
- Thank your water molecules and have them return to their seats. Review the process of phase change that they observed, noting the way that temperature changed the behavior of the molecules.
- Ask the students where the energy that caused the temperature change came from. (The sun.)
- Point out that this process – the phase changes of water powered by the sun – is what drives weather patterns, the movement of water around the globe, and the resulting erosion that shapes our landscape. Also point out that while water changes state and moves around, it is rarely created or destroyed. The water that exists on the planet today is OLD. At one time, the water molecules they drank this morning were once in the oceans when the Earth first formed and perhaps even were drunk by a dinosaur and later peed out again. If you did the mini-investigation, draw an analogy between the mini-investigation and the water cycle. The quantity of water in the bag stayed the same just like the quantity of water on the planet has stayed the same since the planet was formed. Just like in the bags, the water on the planet continually changes state and moves around from place to place.
- Give students the handout and turn on the overhead projector with the water cycle drawing.
- Invite students to name places on or around the planet where water can be found in any of its forms. As students provide one of the 6 major locations where water is stored (surface water, atmosphere, precipitation, glaciers, groundwater, living organisms) fill in that area on the water cycle transparency and have students copy our labels onto their own diagrams. Discuss the importance of each of the storage areas as you label it (see Teacher Background).
- Next, ask students how they think water moves from place to place. As they point out each part of the water cycle (evaporate, condense, melt, freeze, percolate, transpire, drink, excrete) introduce an arrow and a label for the diagram.
- Once the diagrams are completed, read or tell the students a story of a water molecule that makes a journey through the water cycle. An example of a story that follows a drop of water may be found on the USGS site. There is also a Magic School Bus episode by Pat Relf where Ms. Frizzle’s famous class takes a journey through the water cycle.
- Tell the students that they now have the job of telling the story of a water molecule that makes its own journey through the water cycle. Notice that each of the locations where water is stored has a number. Students will roll a dice to figure out where each water molecule will begin and end its journey. On its way, the water molecule must travel through at least 4 different locations including a living organism.
- Allow students time to outline their stories during class and check that each student has a reasonable story outline. The story itself can be completed as homework.
1. Water Cycle Stories - Assessments
- Completed stories can be graded for comprehension.
- If you choose to have students share their stories, have students imagine 2 more steps of the water molecule’s journey.
- If you did the mini-investigation, have students diagram the water molecules at different stages of the experiment.
- Using the stories that students write as a rough draft, help students edit and revise their story and turn the stories into illustrated children’s books. These books can be shared with elementary school students.
- The University Corporation for Atmospheric Research website has fabulous information and resources for teachers. One of many excellent activities shows you how to build a fabulous model of the water cycle with a lamp, a clear plastic box, some clay and some ice. This model may be used to illustrate and visualize the convection currents that cause common weather patterns.
1. Water Cycle Stories - Sources and Standards
The mini-investigation was inspired by the Mini Water Cycle lesson in Water Precious Water by the AIMS Education Foundation.
Using students to model the behavior of molecules in a solid, liquid and gas was inspired by a lesson I observed by Michael Geluardi, a science teacher and friend at Piedmont High School in Oakland, CA.
The story writing part of this lesson was inspired by Activity 3 from the SEPUP unit Groundwater Contamination: Trouble in Fruitvale.
A great resource for additional information about the water cycle may be found on the USGS website.
Shaping Earth’s Surface
Energy in the Earth System
4. Many phenomena on Earth’s surface are affected by the transfer of energy through radiation and convection currents. As a basis for understanding this concept:
a. Students know the sun is the major source of energy for phenomena on Earth’s surface; it powers winds, ocean currents, and the water cycle.
d. Students know convection currents distribute heat in the atmosphere and oceans.
e. Students know differences in pressure, heat, air movement, and humidity result in changes of weather.
Structure of Matter
3. Each of the more than 100 elements of matter has distinct properties and a distinct atomic structure. All forms of matter are composed of one or more of the elements. As a basis for understanding this concept:
e. Students know that in solids the atoms are closely locked in position and can only vibrate; in liquids the atoms and molecules are more loosely connected and can collide with and move past one another; and in gases the atoms and molecules are free to move independently, colliding frequently.
5. Chemical reactions are processes in which atoms are rearranged into different combinations of molecules. As a basis for understanding this concept:
d. Students know physical processes include freezing and boiling, in which a material changes form with no chemical reaction.
Chemistry of Living Systems (Life Sciences)
6. Principles of chemistry underlie the functioning of biological systems. As a basis for understanding this concept:
c. Students know that living organisms have many different kinds of molecules, including small ones, such as water and salt, and very large ones, such as carbohydrates, fats, proteins, and DNA.