CRITICAL THINKING ACTIVITY: THE WATER CYCLE

Student Sheet 1CRITICAL THINKING ACTIVITY:THE WATER CYCLEWater is the onlysubstance that exists onEarth in each of itsthree states and easilychanges from one state toanother. Water sometimeschanges its location bychanging state in acontinuous pattern calledthe water cycle or thehydrologic cycle. Thewater cycle is selfrenewing and continuous. The Sun provides the energy to power the watercycle.When water changes state in the water cycle, the total number of waterparticles remains the same. The changes of state include melting,sublimation, evaporation, freezing, condensation, and deposition. Allchanges of state involve the transfer of energy. The water particles in eachstate behave as energy is absorbed or released. . Condensation, deposition,and freezing are processes that occur as a result of a decrease in the heatenergy of water particles.1

Student Sheet 2When solid ice gains heat, it changes statefrom solid ice to liquid water in a processcalled melting. Ice cubes in a cold drink,for example, gradually melt. Each springyou see snow melt into slush and puddles.Sometimes adding heat energy to solid icecauses a change of state from a solid to agas. This change, directly from a solid to agas without becoming a liquid, is calledsublimation. On crisp, dry winter days youmight notice that snow banks shrink, or icegradually disappears, without first becoming slushy and wet.When water absorbs enoughheat, it becomes a gas (watervapor). This process is calledevaporation. Water vapor(steam) mixes with the air andseems to disappear. A simpleexample is water boiling in ateapot and escaping into theair. Another type ofevaporation occurs from thesurface of plant leaves as theplant’s temperature increasesand water vapor is releasedinto the air as the plant“breathes” in the process oftranspiration.When water vapor loses thermal energy and becomes liquidwater, condensation has occurred. Rain and dew are examplesof condensation. A cold can of pop placed outside on a hotsummer day often accumulates water droplets. This isbecause water vapor in the air condenses when the cold cancools it.2

Student Sheet 3Sometimes, removing heat energy fromwater vapor causes it to become a solid,rather than a liquid. Deposition occurs whenwater vapor changes state directly from agas to a solid. Deposition is the reverse ofsublimation. One example of depositionoccurs high in the atmosphere or on the topof high mountains where the temperature isvery low. In these conditions, water vaporforms snow without becoming a liquid first.Solid water includes permanent ice and snow inglaciers and polar regions, and ice and snowthat form in the winter. Liquid water falls tothe ground in the form of rain. Liquid wateralso forms when winter ice and snow begin tomelt. Much of this water is called runoff.Runoff water flows downhill under theinfluence of gravity, through streams, rivers,and lakes and some eventually reaches theoceans. All the water on Earth’s surface iscalled surface water.Some liquid water seeps into the ground. This water, called groundwater,trickles down through openings in the soil and cracks in rocks until it hitsbedrock and cannot flow down any farther. The water spreads out until it fillsall the available spaces in the loose rock and soil above the bedrockGROUNDWATER3

Student Sheet 4Once water vapor is in theatmosphere, low temperaturescause the vapor to eithercondense into a liquid orundergo deposition to form icecrystals. Water droplets andice crystals in the atmosphereform clouds, which are movedaround the planet by air currents. The water droplets in clouds collide toform larger droplets that fall as rain. Ice crystals fall to the ground assnowflakes. Both rain and snow are forms of precipitation—water that fallsto Earth’s surface. Fallen snow may gradually accumulate as polar ice sheets,icecaps and glaciers.When liquid water losesthermal energy, itundergoes freezing :changing state from aliquid to a solid. We seemany examples of this ineveryday life. Puddles,ponds, lakes, and evenparts of oceans freezewhen the water becomescold enough. At lowtemperatures, Earth’ssurface water freezes and forms solid ice. Ice is slightly less dense thanliquid water. This explains why, in the winter, lakes and ponds develop a layerof ice that floats on the liquid water underneath. As a result, animals andplants can survive through the winter without being frozen solid.Winter snow melts as spring arrives. The snowmelt flows into streams andrivers, and eventually into the oceans. Some of the snowmelt sinks into theground, becoming groundwater, while the surface water evaporates tobecome water vapor, starting the water cycle all over again.4

Student Sheet 5ACTIVITY #1- MODELING AND OBSERVING THE WATER CYCLEOBSERVATIONS:1.2.3.4.5.6.7.8.9.10.5

Student Sheet 6PART 1: DIAGRAM OF OBSERVATION6

Student Sheet 7PART 1: ANALYSIS1. Relate each part of your model to the water cycle diagram at the topright of this page. For example, the lamp represented the sun.What other Earth system processes were demonstrated in thislab?2. What was the energy source for the water cycle?3. How does the water cycle "transport" energy?4. What do you think would happen if you added a second or even thirdlamp?5. Describe what you think would happen if you left the water cycle in ashoebox in the dark for several hour.6. Which parts of the water cycle were clearly demonstrated with thislab and which parts were not well represented?7. How might you document and share your demonstration with otherstudents?8. Draw a sketch of your water cycle model and add words to describethe processes taking place in the model.ACTIVITY 2: CREATIVE WRITINGUse story maps to plan out your story. Remember to use the scientific termsrelated to the water cycle and write in complete sentences. Choose onescenario from the list below.You are a molecule of water (in solid form) sitting on amountaintop in the middle of spring You are surround by millionsof your relatives-all of them snow. The sun is bright and it isstarting to get very warm, when all of a sudden .7

Student Sheet 8You are a molecule of water (in liquid form) floating along happilyin the ocean when suddenly .You are a drop of water (in liquid form) sitting by yourself on arock in the desert. Everyone around you is thirsty. You notice adesert lizard slowly approaching you when suddenly You are a drop of water (in gas form) floating in the air aftersomeone took a hot shower. It is starting to get less and lesshot when suddenly Write a story about a water droplet taking thefollowing journey: Lake - Clouds - Ocean - Cloud- River - Ocean - Clouds - GlacierWrite a story about a water droplet taking thefollowing journey: Lake - Clouds - Ocean - Cloud- River - Ocean - Clouds - Glacier8

THE WATER CYCLE Water is the only substance that exists on Earth in each of its three states and easily changes from one state to another. Water sometimes changes its location by changing state in a continuous pattern called the water cycle or the hydrologic cycle. The water cycle is self-renewing and continuous.