Lesson plan Grade 8 Science
Windward Ridge Water Cycle: Tracing Sun and Gravity
A 45-minute grade 8 science lesson where students model a fictional watershed and label each water-cycle step as driven by the sun's energy or by gravity.
Objectives
- Students will develop a model that traces water through evaporation, condensation, precipitation, runoff, and groundwater flow.
- Students will identify which steps of the cycle are driven by energy from the sun and which are driven by gravity.
Vocabulary
- Evaporation
- Evaporation happens when liquid water, often warmed by the sun, turns into an invisible gas called water vapor that rises into the air. It is how water leaves oceans, lakes, and puddles.
- Condensation
- Condensation is when water vapor in the air cools down and turns back into tiny liquid water droplets. It is how clouds form and why a cold glass gets wet on the outside on a warm day.
- Transpiration
- Transpiration is how plants release water into the air through tiny holes in their leaves. A tree pulls water up from the soil through its roots and lets it escape from its leaves as vapor.
- Infiltration
- Infiltration is when rain or melted snow soaks down into the soil instead of flowing away across the top of it. Water that infiltrates can feed plant roots or keep sinking to become groundwater.
Also: runoff
Teacher overview
Fictional Windward Ridge is a hill with a stream, a small pond, forest, and an aquifer beneath it, which makes it a compact setting for modeling the whole water cycle. This lesson has students build a labeled model of water moving through that watershed and sort each step by its driving force: the sun's energy lifts water upward through evaporation and transpiration, while gravity pulls it back down through precipitation, runoff, and infiltration. A common misconception this lesson addresses is that the water cycle is a single loop from ocean to cloud to rain, with no role for plants, groundwater, or two different energy sources.
Procedure
Hook (5 min): Describe a single raindrop landing on Windward Ridge and ask students to name three different places it could go next. Record answers without judging them, and note whether any student mentions soaking into the ground or being taken up by a tree.
Direct instruction (12 min): Introduce the two driving forces. The sun's energy powers evaporation from the pond and stream and transpiration from the forest, moving water upward as vapor that then cools and condenses into clouds. Gravity powers precipitation as it falls, surface runoff downhill into the stream, and infiltration down into the aquifer. Point out that water can spend about 9 days in the atmosphere but far longer underground, so the cycle runs at very different speeds along different paths.
Guided model-building (15 min): In groups of three, students draw Windward Ridge on chart paper and add labeled arrows for evaporation, transpiration, precipitation, runoff, and infiltration, and mark where rising vapor cools and condenses into clouds. Each movement arrow must be tagged "sun" or "gravity" to show its driving force. Circulate and prompt any group that draws only a single ocean-to-cloud loop.
Formative check (5 min): Each group states one sun-driven step and one gravity-driven step from its model. Poll the class with thumbs up or down on two claims: "precipitation is driven by the sun" (down) and "evaporation is driven by gravity" (down). Reteach briefly if fewer than about 80 percent respond correctly.
Independent exit ticket (8 min): Students complete the three-question handout individually, then turn it in as they leave.
Student Handout
Answer each question in one or two sentences, using your group's Windward Ridge model.
- Name one step in the water cycle that is driven by energy from the sun, and explain what the sun's energy does in that step.
- Name one step that is driven by gravity, and explain what gravity does in that step.
- A parking lot is paved across part of Windward Ridge. Predict how that change affects infiltration and runoff, and name which driving force is involved.
From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.
Answer Key
- Answer: Accept evaporation or transpiration. In evaporation the sun's energy heats water in the pond or stream until it becomes vapor and rises; in transpiration the sun's energy drives water out through the leaves of the forest.
- Answer: Accept precipitation, runoff, or infiltration. In precipitation gravity pulls droplets down as rain or snow; in runoff gravity moves water downhill into the stream; in infiltration gravity pulls water down into the soil and aquifer.
- Answer: Paving reduces infiltration because water can no longer soak into the sealed ground, so more water becomes runoff that gravity carries downhill. Gravity is the driving force for both infiltration and runoff, and the balance between them shifts toward runoff.
Differentiation
Support
Give these students a model with the arrows already drawn but unlabeled, so their task is limited to naming each step and tagging it "sun" or "gravity." Provide a word bank of the six step names.
Extension
Ask students to add a seasonal change to their model, such as winter freezing, and explain how a change in the sun's energy would slow evaporation and store water as snow until warmer weather releases it.
ELL supports
Pair each vocabulary word with a simple icon (a sun over a pond for evaporation, a downward arrow for gravity steps) on a reference card. Allow students to complete the exit ticket with labeled drawings and short phrases rather than full sentences.
Extensions
Have groups trace where the town's drinking water would enter their model, then write a short paragraph connecting the source water a utility collects to the specific water-cycle steps that deliver it, such as runoff into a reservoir or infiltration into a well field.