Materials & Prep
Prepare two identical clear cups, 50 mL of water, a balance, a lamp, a tray, an ice-filled metal or glass cup, and a paper towel. Place one water cup under the lamp and one the same distance from the lamp but not under it. Keep the cup type, water volume, and time the same. Record each cup’s starting mass. If the class cannot wait for measurable results, prepare this data from the same setup: lamp cup, 50.0 g before and 44.0 g after 8 minutes; room-temperature cup, 50.0 g before and 48.0 g after 8 minutes. The lamp represents a source of energy like the Sun, not sunlight itself. Confirm local procedures for electrical equipment, hot lamps, and handling glass before class.
Opening
DisplayShow the two cups and ask, “After eight minutes, one cup has less water. Where did the missing water go?” Students must first write one prediction: “The water because .” Accept possibilities such as disappeared, went into the air, or soaked into something. Do not correct answers yet.
Ask“Which cup should lose more water, and why?” Students vote silently, then briefly share their reasoning. Tell students they will use evidence to decide whether water disappears or changes location.
Model the investigation: Point out that both cups begin with the same amount of water. The only planned difference is exposure to the lamp. The measured outcome is mass after eight minutes.
Direct instruction
ShowReveal the recorded results: the lamp cup changed from 50.0 g to 44.0 g, a loss of 6.0 g. The room-temperature cup changed from 50.0 g to 48.0 g, a loss of 2.0 g. Emphasize that the water did not vanish. Some liquid water changed into water vapor and moved into the air. The lamp supplied energy that made the change happen faster.
Think aloud“I observe that the lamp cup has less mass after eight minutes. I do not directly observe water vapor, so ‘water vapor entered the air’ is an inference that explains the mass decrease. Because the cups began with equal amounts and the lamp was the main difference, the data support the claim that added energy increased evaporation.”
DefineEvaporation is the change from liquid water to water vapor. Condensation is the change from water vapor to liquid water. Precipitation is water falling from clouds as rain, snow, sleet, or hail. Collection is water gathering in oceans, lakes, rivers, soil, or other places.
AnalogyExplain that the Sun is like the power source that gives water particles enough energy to leave liquid water and enter the air. The analogy stops there: the water is not destroyed and the Sun does not pull water upward like a magnet.
DisplayDraw this connected sequence: collection → evaporation → condensation → precipitation → collection. Write “Sun’s energy” beside the arrow from collection to evaporation. Explain that gravity helps precipitation fall and water flow into collection areas, while the Sun supplies the energy that drives evaporation.
ConfrontReturn to the opening prediction. Ask, “What evidence shows that ‘the water disappeared’ is not the best explanation?” Expected response: the water cup lost mass while the water entered the air as vapor, and water vapor can later condense.
Guided practice
ShowHold the ice-filled cup above the tray. Students observe droplets forming on the outside. Ask, “Did the water leak through the cup, or did water vapor in the air change into liquid?” Students commit with a finger vote, then explain their choice. The droplets are condensation: water vapor from the air cooled near the cup and became liquid water.
CompareBuild the cycle from the observations. The lamp demonstration is evidence for evaporation. Droplets on the cold cup are evidence for condensation. Clouds and falling rain are examples of condensation followed by precipitation, and a lake or ocean is a collection area.
Check for understandingStudents complete these three prompts on paper: “Liquid water to water vapor is .” “Water vapor to liquid water is .” “The energy that drives evaporation in Earth’s water cycle comes mainly from .” Have students show answers simultaneously. If any answer is incorrect, reteach using the cup and the arrow diagram before continuing.
Turn and talkPartners explain why the water cycle is called a cycle even though individual water molecules can move through different places. Require the sentence frame: “Water does not disappear. It , then , because .”
Independent explanation
WriteStudents create a water-cycle explanation using the sequence below. They may draw arrows and label each step, but every arrow must include what happens to the water and where energy or gravity matters.
- Water collects in an ocean, lake, river, or puddle.
- The Sun warms the surface water.
- Liquid water changes into water vapor and moves into the air.
- Higher in the atmosphere, water vapor cools and changes into tiny liquid droplets, forming clouds.
- Water falls from clouds as precipitation.
- Water collects again or flows into a collection area.
Students then write a claim-evidence-reasoning response: “Water does not disappear during the water cycle.” Their evidence must use one observation from the cup demonstration or condensation demonstration. Their reasoning must name at least one process and explain the Sun’s role.
ScaffoldProvide the word bank evaporation, condensation, precipitation, collection, water vapor, Sun’s energy, gravity, and the frame “I claim . My evidence is . This supports my claim because .” Students who need an entry point may first arrange the six numbered steps and draw arrows before writing.
CirculateLook specifically for the misconception that clouds are made only of water vapor or that precipitation is the same as evaporation. Ask, “At this step, is the water liquid, solid, or gas?” and “Where did the energy for evaporation come from?”
ExtensionStudents explain what would happen to evaporation and the rest of the cycle if the Sun supplied much less energy. They must distinguish a change in the rate of the cycle from the claim that the cycle would stop instantly.
Closing check
Exit ticketStudents answer independently: “A puddle dries after a sunny day. Describe what happened to the water, name the process, and explain where the energy came from. Then describe how that water could later return to the ground.” Require the words evaporation, water vapor, Sun’s energy, condensation or precipitation, and collection.
Collect: Check that each response describes water changing location or state rather than disappearing, identifies the Sun as the main energy source for evaporation, and connects at least one later process to the water cycle.