MS-ESS2-4NGSS*ScienceEarth and Space ScienceGrades 6-8
MS-ESS2-4: Modeling the Water Cycle, Driven by the Sun and Gravity
In plain English: MS-ESS2-4 is the NGSS middle school performance expectation that asks students to develop a model of how water cycles through Earth's systems, driven by energy from the sun and by the force of gravity. Students build drawn and physical models that show where water changes state and why it moves up or down. It is usually taught in grade 6, 7 or 8 Earth science.
Develop a model to describe the cycling of water through Earth's systems driven by energy from the sun and the force of gravity.
Clarification Statement: Emphasis is on the ways water changes its state as it moves through the multiple pathways of the hydrologic cycle. Examples of models can be conceptual or physical.
Assessment Boundary: A quantitative understanding of the latent heats of vaporization and fusion is not assessed.
Next Generation Science Standards · Disciplinary Core Idea: Earth's Systems · Official standard
Students develop models of the water cycle, the path water takes as it moves again and again among Earth's systems: the air (atmosphere), the oceans, lakes and rivers (hydrosphere), the land and rock (geosphere), snow and ice, and living things. A model is a simplified version of a real system that we use to explain and predict. Students build two kinds: a conceptual model (a labeled drawing with arrows) and a physical model (a box with sand, warm water and a bag of ice). In every model, each arrow answers two questions: does water change state here, and what drives this step, energy from the sun or the force of gravity?
The NGSS Clarification Statement says: "Emphasis is on the ways water changes its state as it moves through the multiple pathways of the hydrologic cycle. Examples of models can be conceptual or physical." The Assessment Boundary says: "A quantitative understanding of the latent heats of vaporization and fusion is not assessed." So students say whether a change of state takes in or gives off energy, but nobody calculates amounts of energy. All data sets on this page are invented for teaching unless a value is described as a real Earth fact. Safety: only the teacher handles warm water, and no student uses a heat source of any kind.
Learning Objectives
By the end of this lesson, students will be able to:
Develop a conceptual model of the water cycle that shows at least eight pathways among the ocean, the air, the land, ice, groundwater and living things
Identify the change of state in each pathway (evaporation, condensation, freezing, melting, sublimation, deposition) and whether water takes in or gives off energy
Explain that energy from the sun drives the pathways that lift water up as a gas, and that gravity drives the pathways that bring water down and downhill
Use a physical model and invented data to support a claim about what drives one part of the cycle, and name what the model leaves out
Prior Knowledge Required
Students should already be comfortable with:
Matter is made of particles too small to see, and water can be a solid, a liquid or a gas 5-PS1-1
Earth's gravity pulls objects down, toward the center of Earth 5-PS2-1
Earth's major systems (air, water, land, living things) interact 5-ESS2-1
Reading a simple line graph and a data table, and finding a difference or a rate
Before class, take a photo of a puddle on the school blacktop in the morning, and another photo of the same spot in the afternoon, when the puddle is gone. Show both photos.
Warm-Up Prompt
"The puddle was here this morning and it is gone now. Where did the water go? List every place it could have gone. For each place, say whether the water went up, down or sideways, and what you think made it move."
Collect ideas on the board in two columns that you do not label yet: ideas where water goes up (into the air) and ideas where water goes down or sideways (into cracks, down a drain, downhill). At the end of Direct Instruction, label the columns "energy from the sun" and "gravity". Many students say the water "dried up" or "disappeared": ask what "dried up" means for the water particles.
Direct Instruction15 minutes
Key words. Water exists as a solid (ice and snow), a liquid and a gas. Water vapor is water as a gas; it is invisible. A change of state is a change from one of these forms to another. Evaporation is liquid to gas, condensation is gas to liquid, melting is solid to liquid, freezing is liquid to solid, sublimation is solid straight to gas, and deposition is gas straight to solid (frost). Evaporation, melting and sublimation happen only when water takes in energy; condensation, freezing and deposition happen when water gives off energy. Other pathways move water without changing its state: precipitation (rain, snow, sleet or hail falling from clouds), runoff (water flowing over the ground), infiltration (water soaking down into soil), groundwater flow (water moving slowly through soil and rock) and transpiration (plants releasing water vapor from their leaves).
Two drivers. Energy from the sun warms water and ice, so it drives evaporation, transpiration, melting and sublimation, and its uneven heating of the air makes the winds that carry water vapor and clouds. Gravity pulls water and ice downward and downhill, so it drives precipitation, runoff, rivers, infiltration, groundwater flow and the slow flow of glaciers. Use Diagram 1 to trace both kinds of arrows.
Sun: evaporation and condensation over the ocean
Sunlight warms the surface of a tropical ocean. Water vapor rises with the warm, moist air. Higher up the air is cooler, and puffy clouds form.
Result: Evaporation (liquid to gas) takes in energy from the sun. As the rising air cools, water vapor condenses (gas to liquid) on tiny specks of dust and salt, making the droplets of a cloud. A cloud is liquid droplets or ice crystals, not water vapor.
Sun: transpiration from a schoolyard tree
A clear plastic bag is tied over a leafy branch for 2 hours (invented data). On a sunny day, 18 mL of water collects in the bag; on a cloudy day, 5 mL collects.
Result: Rates: 18 ÷ 2 = 9 mL per hour in sun and 5 ÷ 2 = 2.5 mL per hour under clouds, 3.6 times as fast in sun. Water leaves the leaves as vapor (transpiration), then condenses on the cooler bag, and gravity pulls the drops into the lowest corner.
Gravity: rain on a lawn
A storm drops 10 mm of rain on a 100 m² lawn.
Result: Volume = 0.010 m × 100 m² = 1.0 m³ = 1,000 L. Gravity pulls the drops down, pulls some water down into the soil (infiltration) and pulls the rest across the ground and into a storm drain (runoff).
Sun and gravity: a valley glacier
A mountain glacier, a thick river of ice, creeps downhill about 0.3 m per day under its own weight. At its lower, warmer end, sunlight melts the ice.
Result: 0.3 m × 365 days ≈ 110 m per year, pulled by gravity. Melting (solid to liquid) takes in energy from the sun, and gravity carries the meltwater down the valley as a stream.
Gravity: from cloud droplets to raindrops
A cloud droplet is about 0.02 mm across and is held up by rising air. A raindrop is about 2 mm across.
Result: The raindrop is 100 times as wide, so it holds 100 × 100 × 100 = 1,000,000 droplets of water. Droplets bump and join until a drop is heavy enough for gravity to pull it down through the rising air.
After each example, ask: "Which arrow would you draw for this in Diagram 1, does water change state, and is it driven by the sun or by gravity?" Then ask what would happen to the cycle if one of the two drivers disappeared. Leave the question open: students return to it in the homework and the quiz.
Guided Practice10-15 minutes
Pairs analyze invented data from a mountain weather station and a river gauge in the valley below it. The snow depth is measured at the station; the river flow is the volume of water passing the gauge each second.
Guided practice data (invented): mountain snow and valley river
Month (day 1)
Snow depth at the station (cm)
River flow in the valley (m³/s)
March
180
8
April
165
12
May
90
35
June
10
48
July
0
20
Find how much the snow depth drops between each pair of months. Between which two months does it drop the most?
In which month is the river flow highest? How does that month compare with the time of fastest snow loss?
Draw a two-arrow model from the snow to the river. Label one arrow with the change of state and the sun, and the other with the movement and gravity.
Why does the river flow fall in July even though summer sunshine is strongest? Use your model to explain.
Debrief: the snow loses 80 cm between May and June, its largest drop, and the river peaks in June, so the data support a model in which sunlight melts the snow (solid to liquid) and gravity carries the meltwater down to the river. By July the snow is gone, so there is no meltwater left to feed the river.
Independent Practice10-15 minutes
Each student draws a conceptual model of the water cycle for a farm valley with a reservoir (a lake made by a dam), a field of corn, a forested hill and a town well that pumps groundwater. The model must:
Show at least eight arrows that connect the air, clouds, the hill, the reservoir, the field, the soil and the groundwater.
Label each arrow with its pathway, the change of state if there is one, and the driver: sun (solid blue arrow) or gravity (dashed black arrow).
Include at least one arrow that carries water uphill or upward, and explain in one sentence what makes that possible.
Use the model to predict one change during a hot, dry week in July, and name the arrow that changes.
Circulate and ask each student to point to one arrow that starts in a living thing and one that ends underground. Students keep the model for the exit ticket.
Closure5 minutes
Exit ticket: "Pick one arrow in your farm valley model that the sun drives and one that gravity drives. For each, write the change of state (or 'no change') and one observation you could make in your own neighborhood that would be evidence for it." Return to the warm-up columns and label them together: the "up" column is energy from the sun and the "down or sideways" column is gravity.
Differentiation Strategies
For Struggling Students
Give a partly finished copy of Diagram 1 with the places drawn and the arrows blank, plus a word bank of the pathway names
Use two colors of sticky notes for arrows: blue for "the sun lifts it" and black for "gravity pulls it"
Pair each change of state with a kitchen example before the Earth example: ice melting in a glass, a bathroom mirror fogging after a shower
For Advanced Students
Ask students to add arrow widths that show how much water moves along each pathway, and to justify which arrows should be widest
Have students model what happens to the cycle in a desert valley and in a rain forest, and compare the two models
Ask students to find a pathway that could be driven by both the sun and gravity, such as snowmelt reaching a river, and to split it into two arrows
Assessment Guidance
What to Look For
Check that every arrow in a student model has a direction, a pathway name and a driver, and that changes of state are named correctly (condensation is gas to liquid, not "steam turning into air"). Listen for the idea that clouds are water vapor: clouds are liquid droplets or ice crystals. Look for models that show water only going round one circle (ocean, cloud, rain, ocean) and push for groundwater, ice and living things. Students should say that the sun gets water up into the air and gravity brings it down.
02
Classroom Activities
3 Activities
1
Water Cycle in a Box: A Physical Model
25 minGroups of 3-4
Groups build a physical model of the water cycle in a clear plastic storage box. One end holds a sloped "mountain" of damp sand and the other end a "sea" of water. A zip-top bag of ice on the lid, above the mountain, cools the air the way height does. Two boxes are compared: one sea is warm tap water to stand in for water warmed by the sun, and one is cold tap water.
Procedure
Pile 3 L of damp sand at one end of each box to make a slope. Set a small plastic cup (the "mountain lake") on top of the slope, below where the ice bag will sit.
The teacher pours 1 L of warm tap water into the low end of box A and 1 L of cold tap water into box B. The teacher checks the warm water with a thermometer and adds cold water if it is above about 45 °C.
Put the lids on and set a zip-top bag with 10 ice cubes on each lid, above the cup. Place both boxes in the same spot, out of drafts.
Every 15 minutes for 45 minutes, look for droplets under the lid and measure the water in the cup with a graduated cylinder, then pour it back onto the sand slope and watch where it goes.
Safety: only the teacher pours warm water. Wipe up spills right away so no one slips, and wash hands after handling the sand.
Sample Data (invented)
Water collected in the cup at 15, 30 and 45 minutes. Box A (warm sea): 3, 7 and 12 mL. Box B (cold sea): 0, 1 and 1 mL. Box A showed a fog of droplets under the whole lid after 10 minutes; box B showed only a few droplets under the ice bag.
Discussion Questions
Box A collected more water than box B at every reading. What does the warm water stand for, and what does the difference tell you about the role of the sun?
Which parts of the box model evaporation, condensation, precipitation and runoff? For each one, is the driver the warm water (the sun) or gravity?
Why do drops fall from the lid only after they grow, and never fall upward?
Name two parts of the real water cycle that this model leaves out, and suggest how you could add one of them.
Modification for Distance Learning
Students build a small version at home with a large clear bowl, plastic wrap, a cup of cold water from the tap as the "sea" (no hot water), and a bag of ice on top, or they analyze the sample data above. They post a labeled photo of the model with each arrow marked sun or gravity.
2
Place Cards: Build and Test a Conceptual Model
20 minGroups of 3
Each group gets 10 place cards and builds a conceptual model on chart paper by drawing arrows between them. Then the teacher reads "test cards" with new conditions, and groups use the model to predict which arrows get stronger or weaker.
The 10 Place Cards
Ocean; water vapor in the air; clouds; snow and glaciers on a mountain; a lake; a river; soil; groundwater; plants; animals (including people).
Procedure
Tape the cards onto chart paper where they belong: the air and clouds near the top, the ground and groundwater near the bottom.
Draw an arrow for every way water moves between two cards. Use a blue marker and a solid line when the sun drives the step, and a black marker and a dashed line when gravity drives it.
Write the pathway name and the change of state (or "no change") on every arrow. Aim for at least 12 arrows.
Check: every card must have at least one arrow in and one arrow out.
Test Cards
Test 1: "A month of cloudy, cool weather."
Test 2: "A heavy winter of snow, then a warm spring."
Test 3: "A parking lot is built over half of the soil."
For each test card, groups circle the arrows that change and write one sentence of prediction.
Discussion Questions
Which card has the most arrows leaving it in your model? Is it the same in other groups?
Which arrows lift water up? What drives every one of them?
Which test card changes mostly gravity-driven arrows? How can a change on the ground affect pathways that gravity drives?
Modification for Distance Learning
Students build the model on a shared online whiteboard with the 10 cards as movable boxes and two arrow styles, then record a one-minute explanation of one test card.
3
Puddle Watch: Sun Against Shade
20 min (plus quick checks)Pairs
The class makes two puddles of the same size on the school blacktop, one in full sun and one in the shade of a building, and traces their outlines with chalk each hour. Pairs turn the outlines into areas and use the data as evidence for what drives evaporation. They also note which way each puddle spreads at first.
Procedure
On a dry morning, choose a flat sunny spot and a flat shaded spot. Pour 2.0 L of water from a pitcher onto each spot from the same height.
Draw a chalk grid of 10 cm squares around each puddle. Trace the outline right away and again after 1, 2 and 3 hours (teacher or a pair during passing time).
Count the squares inside each outline (count a square if more than half of it is wet) and turn the count into square meters: 100 squares = 1 m².
Note where each puddle spreads in the first minute and where its last wet spot is.
Safety: work only in an area closed to cars, stay out of the way of other classes, and wear sunscreen and a hat.
Sample Data (invented)
Area of the sunny puddle at 0, 1, 2 and 3 hours: 1.20, 0.82, 0.46 and 0.12 m². Area of the shaded puddle: 1.20, 1.08, 0.97 and 0.85 m². Both puddles first spread toward a low corner of the blacktop, and their last wet spots were in small dips.
Discussion Questions
How much area did each puddle lose in 3 hours? Use the numbers to compare the two puddles.
Diagram 2 shows these data. Which line is steeper, and what does the steepness tell you about evaporation?
Which observation in the data is evidence that gravity acted on the puddles, and which change of state took the water away?
Some water may also have soaked into cracks in the blacktop. Which arrow in Diagram 1 would that be, and how could you change the investigation to rule it out?
Modification for Distance Learning
Students pour 1 cup of water on a driveway or sidewalk at home (with a parent's permission), trace it with chalk or take photos next to a ruler every 30 minutes, and compare their results with the sample data.
03
Diagrams & Visual Aids
2 diagrams
Diagram 1: A Conceptual Model of the Water Cycle
A conceptual model of the water cycle (not to scale). Solid blue arrows are pathways driven by energy from the sun: evaporation, transpiration, sublimation, melting, and the wind that carries water vapor and clouds. Dashed black arrows are pathways driven by gravity: precipitation, runoff and rivers, infiltration and groundwater flow. Condensation forms the clouds where rising air cools.
Diagram 2: Puddle Area in Sun and Shade (Invented Data)
The Activity 3 sample data, drawn to scale. Both puddles start at 1.20 m². The steeper the line, the faster the puddle loses area. Students use the two slopes as evidence in the Activity 3 discussion.
04
Homework Assignment
~30 min
MS-ESS2-4 Homework: Building and Using Water Cycle Models
Directions: All data are invented for practice. For each problem, draw or describe the model you use, label every arrow with its pathway and its driver (the sun or gravity), and name any change of state. Show your calculations with units.
Part 1: Building and Critiquing Models (Problems 1-3)
A classmate's model of the water cycle has only four arrows in a circle: water evaporates from the ocean, condenses into clouds, rains onto land, and flows in rivers back to the ocean. (a) Name three pathways the model leaves out, and say where each arrow would start and end. (b) Label all seven arrows (the four given and your three) with their driver: the sun or gravity.
On a humid summer day, you carry a glass of ice water outside. Within a few minutes, drops form on the outside of the glass, grow, and slide down to make a ring of water on the table. (a) Where did the water on the outside of the glass come from? Name the change of state and say whether the water took in or gave off energy. (b) Why do the drops slide down only after they grow? (c) Which part of the water cycle does the glass model? Name two things in the real cycle that it leaves out.
A large bowl holds 1 L of salty water. A small empty cup sits in the middle, and plastic wrap covers the bowl with a pebble on the wrap above the cup. After 6 hours in the sun, the cup holds 45 mL of water. On a cloudy day, the same setup collects 12 mL in 6 hours. (a) Which steps in this model are driven by the sun, and which by gravity? (b) How many times as much water was collected on the sunny day? (c) The water in the cup leaves no white crust when it dries, but the bowl water does. What does this show about evaporation? (d) Predict how much water the setup would collect overnight, and explain.
Part 2: Using Data as Evidence (Problems 4-6)
A 20 mm rainstorm falls on a school's 500 m² parking lot and on its 500 m² grass field. Measurements at the drains show that 9,000 L ran off the parking lot and 2,000 L ran off the field. (a) What volume of rain fell on each area? (b) What percent of the rain ran off each area? (c) Where did the rest of the field's rain go? Name two pathways and their drivers.
A storm soaks a hillside in week 1. A spring at the bottom of the hill flows at 3, 3, 4, 9, 7 and 5 L per minute in weeks 0 to 5 (week 0 is just before the storm). (a) In which week is the flow highest, and how many times the week-0 flow is it? (b) Why does the spring not reach its highest flow in the week of the storm? Use the pathways in Diagram 1. (c) What drives the water from the hilltop to the spring?
A student claims: "The sun is the only thing that powers the water cycle." Write a claim, evidence and reasoning response. Use at least two pathways from this lesson as evidence that gravity is also needed, and explain why the cycle would still stop without the sun.
Rubric
Criterion
Full Credit (2 pts)
Partial Credit (1 pt)
Model
Every arrow has a direction, a pathway name and a driver; changes of state are named correctly
Model is present, but an arrow is missing a label or a change of state is wrong
Sun and Gravity
Explains that the sun drives the pathways that lift water and gravity drives the ones that bring it down
Names drivers without linking them to the direction water moves
Data and Calculations
Volumes, rates, percents and comparisons are correct, with units
Method is right but one value or unit is wrong
Evidence and Limits
Uses data as evidence for a claim and names what a model leaves out
Claim is given, but the evidence or the limits are missing
05
Quiz: 20 Questions
Interactive, with answers
Instructions
Use the water cycle models from the lesson. All data are invented for practice. Your score updates as you answer, and Reset quiz clears everything so you or your students can try again.
Multiple choice: pick an option to check it. Short answer: write your answer, then reveal the model answer.
0 of 20 answered · 0 correct
Question 1 of 20 · Multiple Choice
On a cool, clear morning, the grass is covered with drops of water, but it did not rain during the night. Where did the drops come from?
Answer: A
The drops are dew: water vapor in the air gives off energy to the grass, which cooled overnight, and condenses (gas to liquid). Choice B uses evaporation, which turns liquid into gas, the opposite direction. Choice C adds precipitation that the clear night rules out. Choice D is wrong because there is no ice in the air on a night warm enough for liquid dew.
Question 2 of 20 · Multiple Choice
Which step of the water cycle is driven mainly by gravity?
Answer: D
Infiltration happens because gravity pulls liquid water down into the spaces in soil. Choice A is evaporation and choice C is transpiration, both driven by energy from the sun. Choice B is melting, which also needs energy from the sun.
Question 3 of 20 · Multiple Choice
A pile of snow on a mountain shrinks during a cold, sunny, windy week. The snow stays below 0 °C the whole time, and no meltwater appears. What happened to the missing snow?
Answer: C
Sublimation turns ice straight into water vapor. Energy from sunlight drives it, and dry wind carries the vapor away. Choice A needs the snow to warm to 0 °C and melt, which the question rules out. Choice B confuses gravity with a change of state: gravity cannot pull ice into solid rock. Choice D names condensation, which turns a gas into a liquid; the snow is a solid.
Question 4 of 20 · Multiple Choice
A student puts damp soil and a small plant inside a closed clear plastic bottle and sets it in a sunny window. Each afternoon, drops form on the inside of the bottle and run back down to the soil. In this physical model, what do the drops running down the inside wall stand for?
Answer: D
The drops are liquid water moving downward, so they stand for precipitation and runoff, which gravity drives. Choices A and B describe how water gets into the air in the bottle (evaporation from the soil and transpiration from the plant), not the drops coming down. Choice C describes wind; the drops are liquid, not vapor.
Question 5 of 20 · Multiple Choice
Two identical wet towels are hung outside on the same calm day. The towel in full sun is dry after 2 hours. The towel in the shade of a building is dry after 5 hours. Which conclusion do these data support best?
Answer: B
Both towels lose their water by evaporation, and the one that gets more energy from sunlight dries in less than half the time. Choice A credits gravity, but gravity pulls equally hard in sun and shade, so it cannot explain the difference. Choice C reverses the result: both towels lost water. Choice D is wrong because melting turns a solid into a liquid, and nothing was frozen.
Question 6 of 20 · Multiple Choice
On a cold morning, you breathe out and see a small cloud in front of your face. What is that cloud made of?
Answer: A
Your warm breath holds water vapor. In the cold air it cools and condenses into tiny liquid droplets, the same change that makes a cloud in the sky. Choice B is the gas before it condenses; water vapor is invisible, so it is not what you see. Choice C is also an invisible gas. Choice D is wrong because your mouth is far too warm for ice to form.
Question 7 of 20 · Multiple Choice
In a water cycle model, the width of each arrow shows how much water moves. A student draws the widest water vapor arrow rising from a forest. Which change makes the model match Earth better?
Answer: A
The ocean covers about 71% of Earth's surface and holds about 97% of its water, so far more water evaporates from the ocean than from any other place. Choice B is wrong because sublimation from cold glaciers adds only a small amount of vapor. Choice C makes the model worse: transpiration is a real pathway and an important one over land. Choice D ignores the real differences between the pathways.
Question 8 of 20 · Multiple Choice
Rain soaks into a hillside. Weeks later, some of that water seeps out of the bank of a stream at the bottom of the hill. What moved the water through the ground to the stream?
Answer: D
Groundwater moves slowly through spaces in soil and rock from higher places to lower places, pulled by gravity. Choice A is wrong because the sun drives evaporation at the surface but does not push water sideways through the ground. Choice C confuses moving air with moving groundwater. Choice B reverses what roots do: they take water in.
Question 9 of 20 · Multiple Choice
A small lake has no streams flowing in or out, and no rain falls for two weeks. Its level drops 2 cm in a cool, cloudy week and 5 cm in the next week, which is hot and sunny. Which explanation fits these data best?
Answer: C
The only difference between the weeks is the weather, and more sunshine gives more energy for evaporation, so the level drops faster. Choice A credits infiltration, which depends on the soil under the lake, not on sunshine, so nothing in the data points to it. Choice B is wrong because gravity does not change from week to week. Choice D would add water to the lake and raise its level.
Question 10 of 20 · Multiple Choice
In a student's model, an arrow points from a cloud down to the ocean and is labeled "Evaporation, driven by the sun." How should the label be fixed?
Answer: B
Water falling from a cloud is precipitation, and gravity pulls the drops down once they are heavy enough. Choice A names condensation, which forms cloud droplets but does not move water down to the ocean. Choice C has the right pathway with the wrong driver: the sun lifts water, it does not drop it. Choice D names a pathway that starts in plants.
Question 11 of 20 · Multiple Choice
A stream flows out from the bottom of a mountain glacier. On a sunny summer day, the stream is 30 cm deep at 6 a.m., 38 cm at noon, 52 cm at 5 p.m. and 41 cm at 10 p.m. Which model explains the timing of the deepest water best?
Answer: C
The strongest sunlight comes around midday, so melting is fastest then. The meltwater then flows over, through and under the glacier, pulled by gravity, which takes hours, so the stream is deepest at 5 p.m. Choice A is wrong because gravity does not change during the day. Choice B puts the extra water at night, when the stream is falling. Choice D is wrong because evaporation would remove water and make the stream shallower.
Question 12 of 20 · Multiple Choice
Which of these events can happen only if the water takes in energy, for example from sunlight?
Answer: D
An icicle drips because its ice is melting (solid to liquid), and melting needs added energy, here from sunlight. Choice A is condensation, choice B is freezing and choice C is deposition: in all three, water gives off energy, so they happen when water cools.
Question 13 of 20 · Multiple Choice
A weather station measures evaporation with a pan of water whose surface area is 2,000 cm². On a sunny day, the water level in the pan drops 5 mm. What volume of water evaporated? (1 cm³ = 1 mL.)
Answer: C
5 mm = 0.5 cm, and 0.5 cm × 2,000 cm² = 1,000 cm³ = 1,000 mL = 1.0 L. Choice A multiplies 5 × 2,000 = 10,000 cm³ without changing millimeters to centimeters. Choice B changes 5 mm to 0.05 cm instead of 0.5 cm. Choice D divides 2,000 by 5 instead of multiplying.
Question 14 of 20 · Multiple Choice
Which observation is the best evidence that gravity, not the sun, moves water in that step of the cycle?
Answer: B
Water that always ends up in the lowest place is being pulled downhill by gravity. Choices A and D link faster water loss to more sunlight, which is evidence for the sun driving evaporation and transpiration. Choice C is evidence that sunlight warms the lake and drives evaporation, followed by condensation.
Question 15 of 20 · Short Answer
Trace one water particle from the ocean to a lake high in the mountains. Name at least three steps, the change of state in each step (or "no change"), and whether energy from the sun or gravity drives each one.
Model answer: (1) Evaporation from the ocean: liquid to gas, driven by the sun. (2) Wind carries the vapor inland and up the mountain: no change, driven by the sun's uneven heating of the air. (3) Condensation into cloud droplets or ice crystals as the air rises and cools: gas to liquid or solid, the water gives off energy. (4) Precipitation as rain or snow on the slopes above the lake: no change, driven by gravity. (5) Runoff downhill into the lake, or melting of the snow (sun) and then runoff (gravity). Look for a sun-driven step that lifts the water and a gravity-driven step that brings it down into the lake.
Question 16 of 20 · Short Answer
Imagine that Earth kept its gravity but the sun's energy stopped reaching it. Use your water cycle model to predict what would happen. Name one pathway that would stop and one that would keep going for a while.
Model answer: Evaporation, transpiration, sublimation and melting would stop, because they need energy from the sun, so no new water would rise into the air. Rivers, runoff and groundwater flow would keep going for a while, because gravity still pulls water downhill. The water would collect in the lowest places (the ocean, lakes and underground) and freeze, and the cycle would stop because nothing lifts water back up.
Question 17 of 20 · Short Answer
A plastic bag is tied over the leaves of a potted bean plant. In 3 hours in a sunny window, 6 mL of water collects in the bag. In 3 hours in a shady corner, 2 mL collects (invented data). (a) Find the rate in each place in mL per hour. (b) What do the data show about the role of the sun? (c) The water in the plant came from the soil. What pulled it down into the soil when the plant was watered?
(a) Sunny: 6 ÷ 3 = 2 mL per hour. Shady: 2 ÷ 3 ≈ 0.67 mL per hour. (b) Transpiration is 3 times as fast in the sun, so energy from sunlight speeds up the pathway that moves water from the plant into the air. The drops in the bag then form by condensation. (c) Gravity pulled the water down into the soil (infiltration).
Question 18 of 20 · Short Answer
Plan an investigation with a physical model to test whether a steeper slope makes more rainwater run off instead of soaking in. Name what you change, what you keep the same, what you measure, and one safety rule.
Model answer: Change only the slope: trays of the same soil propped at a gentle angle and a steep angle (for example 10° and 30°, checked with a protractor). Keep the same: the soil type, how damp and packed it is, the amount of "rain" (for example 500 mL poured through a watering can) and how fast it is poured. Measure: the volume of water that runs off into a container at the low end of each tray, with a measuring cup; the rest soaked in. Repeat each slope at least twice. Safety: work over a sink or tub and wipe up spills so no one slips. Look for one changed variable and a measurement in units, and the idea that gravity drives both runoff and infiltration.
Question 19 of 20 · Short Answer
On a cold, clear night, frost forms on a car windshield. At 10 a.m. the sun shines on the windshield: first it is wet, and by noon it is dry. Name the three changes of state in order. For each, say whether the water took in or gave off energy and where that energy came from or went.
(1) Deposition (gas to solid): water vapor in the air gave off energy to the cold glass and became frost. (2) Melting (solid to liquid): the frost took in energy from sunlight. (3) Evaporation (liquid to gas): the water took in more energy from sunlight and went back into the air as water vapor.
Question 20 of 20 · Short Answer
During one sunny week, a backyard pond starts 50 cm deep. Evaporation lowers it 3 cm, one rain shower adds 2 cm, a small stream adds 4 cm, and seepage into the ground lowers it 1 cm. (a) Find the depth at the end of the week. (b) Label each of the four pathways as driven by the sun or by gravity.
(a) 50 - 3 + 2 + 4 - 1 = 52 cm. (b) Evaporation: sun. Rain: gravity (the sun lifted that water into the air earlier). The stream: gravity, flowing downhill. Seepage into the ground (infiltration): gravity.
0 of 20 answered · 0 correct
06
Frequently Asked Questions
10 Questions
What does MS-ESS2-4 mean?
MS-ESS2-4 asks middle school students to develop a model of how water cycles through Earth's systems, driven by energy from the sun and by gravity. The focus is on how water changes state (evaporating, condensing, freezing, melting) as it moves along many pathways. The code stands for Middle School, Earth and Space Science, core idea 2 (Earth's Systems), performance expectation 4.
What grade is MS-ESS2-4 taught in?
It can be taught in grade 6, 7 or 8, because NGSS middle school standards are written for the grade 6-8 band and each state or district decides the order. It often sits in an Earth science unit on weather and climate, before MS-ESS2-5 (air masses and weather) and MS-ESS2-6 (circulation and climate).
What is the assessment boundary for MS-ESS2-4?
The Assessment Boundary says a quantitative understanding of the latent heats of vaporization and fusion is not assessed. Students should know that evaporation and melting take in energy and that condensation and freezing give it off, but they do not calculate how many joules a change of state needs.
What counts as a model of the water cycle?
Any simplified version of the real cycle that students can use to explain or predict. The Clarification Statement names conceptual models, such as labeled drawings and flow charts with arrows, and physical models, such as a box or bowl where water evaporates, condenses and drips. A good model shows the direction of every arrow, the change of state, and what drives each step.
How does the sun drive the water cycle?
Sunlight gives water and ice the energy they need to change into water vapor (evaporation and sublimation) and to melt. It also powers transpiration from plants, and its uneven heating of Earth's surface makes the winds that carry water vapor and clouds. Every pathway that lifts water up into the air depends on the sun.
What does gravity do in the water cycle?
Gravity pulls water and ice down and downhill. It makes rain and snow fall from clouds once the drops or crystals are heavy enough, and it moves water over the ground (runoff), into the soil (infiltration), through the ground (groundwater flow), along rivers to the sea, and down valleys as glaciers.
Are clouds made of water vapor?
No. Water vapor is an invisible gas. Clouds are made of liquid water and ice in pieces far too small to see one by one; they form when water vapor condenses or deposits as air rises and cools. This is a frequent mix-up.
Is the water cycle one big circle?
No. A water particle can take many paths: it may evaporate from the ocean and rain back on the ocean in days, or fall as snow, sit in a glacier for centuries, melt, soak into the ground and move through groundwater for thousands of years. Models with only four arrows in a circle leave out groundwater, ice and living things.
What is a safe water cycle lab for middle school?
A clear plastic box or bowl with damp sand, tap water and a bag of ice on the lid shows evaporation, condensation, precipitation and runoff without any heat source. If you want warm water, the teacher pours warm tap water and checks that it is below about 45 °C. Puddle investigations outdoors use only water and sunlight.
How does MS-ESS2-4 connect to high school science?
It prepares students for HS-ESS2-5, where they plan investigations of the properties of water and its effects on Earth materials, and for high school work on energy in Earth systems. In middle school, it also links to MS-PS1-4 (particle models of changes of state) and leads into MS-ESS2-5 and MS-ESS2-6 on weather and climate.
07
Related Standards
5 standards
These standards connect to MS-ESS2-4: prerequisites to review first, parallel standards at the same level, and next steps that build on it.
Before this lesson
5-ESS2-1Prerequisite
Model ways the geosphere, biosphere, hydrosphere and atmosphere interact
Lesson coming soon
5-PS2-1Prerequisite
Argue that the gravitational force exerted by Earth on objects is directed down
Lesson coming soon
Alongside
MS-PS1-4Parallel
Model how particle motion, temperature and state change when thermal energy changes
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