Basic 7 · Science · Earth Science
The Water Cycle
In this topic you will explain the water cycle as a repeated pattern in nature, describe its stages, and demonstrate evaporation and condensation.
By the end of these notes you should be able to:
- Explain the meaning of the water cycle
- Describe the stages of the water cycle
- Demonstrate evaporation and condensation
What you already know
- Changes of state
Copy everything that has a blue line on its left into your notebook. The other parts are for reading.
Lesson 1
- Strand
- Cycles
- Sub-strand
- Earth Science
- Indicator
- B7.2.1.1.1 – Explain how the water cycle occurs as a repeated pattern in nature
Introduction
The water you drink today may once have been part of the sea at Cape Coast, a cloud over Kumasi or rain on a farm in Tamale. Water moves round and round the Earth in a never-ending journey.
1. Meaning of the Water Cycle
Water cycle: The continuous movement of water between the Earth's surface and the atmosphere through evaporation, condensation and precipitation.
The water cycle is called a cycle because it repeats itself without a beginning or an end. The total amount of water on Earth stays almost the same; it only changes its form and location.
2. Where Water Is Found
| Store | Description |
|---|---|
| oceans and seas | hold most of Earth's water (salty) |
| ice caps and glaciers | frozen fresh water near the poles and on mountains |
| underground water | water stored in rocks and soil (groundwater) |
| rivers, lakes and reservoirs | fresh water on the surface, such as the Volta and Lake Bosomtwe |
| atmosphere | water vapour and clouds |
| living things | water in plants, animals and people |
3. The Sun Drives the Cycle
Energy from the sun heats water in seas, rivers and lakes and turns it into water vapour. Gravity pulls water back down as rain. Without the sun's heat and the pull of gravity, the water cycle would stop.
4. A Repeated Pattern
Each day in the rainy season, the same pattern can be seen: in the morning the sun heats the land and water, water vapour rises, clouds build up in the afternoon, and heavy rain may fall in the evening. The rain fills rivers and soaks into the ground, and the next day the cycle continues.
New words
- water cycle
- The continuous movement of water on Earth.
- water vapour
- Water in the form of a gas.
- atmosphere
- The layer of air surrounding the Earth.
- groundwater
- Water stored under the ground.
Summary
- The water cycle is the continuous movement of water between the Earth and the atmosphere.
- Water is stored in oceans, ice, groundwater, rivers, lakes, the air and living things.
- The sun's heat and gravity drive the cycle in a repeated pattern.
Class activity: Water Stores Poster
- List places where water is stored in your community.
- Show how water moves from one store to another.
- Present your poster to the class.
You need: Printed water-cycle diagram, Printed water-cycle stage cards, Printed photographs of Ghanaian rain clouds
Exercises
Answer in your exercise book first, then check your answers.
1. What powers the water cycle?
- A. the sun
- B. the moon
- C. the wind only
- D. the soil
Show answer
Answer: the sunHeat energy.2. Most of Earth's water is found in…
- A. oceans
- B. rivers
- C. clouds
- D. living things
Show answer
Answer: oceansSalty water.3. The total amount of water on Earth stays almost the same.
- A. True
- B. False
Show answer
Answer: TrueIt only changes form.4. Water in the form of a gas is called water ______.
Show answer
Answer: vapourGas state.5. Name four places where water is stored on Earth.
Show answer
Answer: Oceans, rivers, underground, atmosphere (or ice, living things).Any four.6. Why is the water cycle described as a cycle?
Show answer
Answer: It repeats continuously without beginning or end, moving water between the Earth and the air.Repeated pattern.
Lesson 2
- Strand
- Cycles
- Sub-strand
- Earth Science
- Indicator
- B7.2.1.1.1 – Explain how the water cycle occurs as a repeated pattern in nature
Introduction
The water cycle has several stages. Each stage changes water from one state to another or moves it from one place to another.
1. The Main Stages
| Stage | What happens |
|---|---|
| evaporation | the sun heats water and it changes into water vapour |
| transpiration | plants release water vapour through their leaves |
| condensation | water vapour cools and turns into tiny droplets that form clouds |
| precipitation | water falls from clouds as rain, hail or snow |
| run-off | rainwater flows over the land into rivers and the sea |
| infiltration | rainwater soaks into the soil to become groundwater |
| collection | water gathers in rivers, lakes, seas and underground |
2. Evaporation and Transpiration
Evaporation happens fastest when it is hot, windy and dry. That is why wet clothes dry quickly during the harmattan. Transpiration from plants also adds water vapour to the air; a large tree can release hundreds of litres of water in a day. Together, evaporation and transpiration are called evapotranspiration.
3. Condensation and Precipitation
As warm, moist air rises, it cools. Cool air cannot hold as much water vapour, so the vapour condenses on tiny dust particles to form droplets. Millions of droplets form a cloud. When the droplets join together and become too heavy, they fall as precipitation. In Ghana, precipitation falls mostly as rain.
4. Run-off and Infiltration
When rain reaches the ground, some flows over the surface as run-off into streams and rivers, and some soaks into the soil by infiltration. Forests and grass slow down run-off and help more water to infiltrate, which refills wells and boreholes. Concrete and bare land increase run-off and can cause flooding.
New words
- evaporation
- Liquid water changing into water vapour.
- condensation
- Water vapour changing into liquid water.
- precipitation
- Water falling from clouds as rain, hail or snow.
- infiltration
- Water soaking into the ground.
Summary
- The stages are evaporation, transpiration, condensation, precipitation, run-off, infiltration and collection.
- Heat and wind speed up evaporation; cooling of rising air causes condensation.
- Vegetation increases infiltration and reduces flooding.
Class activity: Water Cycle Cards
- Arrange printed stage cards in the correct order.
- Explain what happens at each stage.
- Act out the cycle, with each learner playing one stage.
You need: Printed water-cycle diagram, Printed water-cycle stage cards, Printed photographs of Ghanaian rain clouds
Exercises
Answer in your exercise book first, then check your answers.
1. Rain falling from clouds is called…
- A. precipitation
- B. evaporation
- C. condensation
- D. transpiration
Show answer
Answer: precipitationFalling water.2. Water soaking into the soil is…
- A. infiltration
- B. run-off
- C. evaporation
- D. condensation
Show answer
Answer: infiltrationInto the ground.3. Plants release water vapour through transpiration.
- A. True
- B. False
Show answer
Answer: TrueThrough leaves.4. Water vapour cooling to form droplets is ______.
Show answer
Answer: condensationCloud formation.5. List the stages of the water cycle in order.
Show answer
Answer: Evaporation and transpiration, condensation, precipitation, run-off and infiltration, collection.Order.6. Explain why cutting down forests can increase flooding.
Show answer
Answer: Without trees and grass, less water infiltrates and more runs off quickly into rivers and low areas.Run-off.
Lesson 3
- Strand
- Cycles
- Sub-strand
- Earth Science
- Indicator
- B7.2.1.1.1 – Explain how the water cycle occurs as a repeated pattern in nature
Introduction
You can see evaporation and condensation in your own kitchen. When a pot of water boils, steam rises; when the steam touches a cold lid, water droplets form.
1. Demonstrating Evaporation
- Pour equal amounts of water into two saucers.
- Place one in the sun and one in the shade.
- Mark the water level on each and check after two hours.
- Observe that the saucer in the sun loses more water.
This shows that heat increases evaporation. The water has not disappeared; it has changed into invisible water vapour in the air.
2. Demonstrating Condensation
- The teacher boils water in a kettle (learners stand at a safe distance).
- Hold a cold metal plate or tray above the steam using a cloth.
- Observe droplets forming on the underside of the plate.
- Watch the droplets join together and drip down.
3. Explaining the Results
The steam from the kettle is water vapour. When it touches the cold plate, it loses heat and condenses into liquid droplets. The dripping droplets model rain falling from clouds. This simple experiment shows two key stages of the water cycle: evaporation (or boiling) and condensation leading to precipitation.
4. Everyday Examples
| Example | Process |
|---|---|
| wet clothes drying on a line | evaporation |
| sweat drying from the skin and cooling the body | evaporation |
| water droplets on a cold bottle of drink | condensation |
| mist on a mirror after a hot bath | condensation |
| morning dew on grass | condensation |
Safety: Only the teacher should handle boiling water. Stand back from the steam to avoid burns.
New words
- steam
- Hot water vapour from boiling water.
- dew
- Water droplets that condense on cool surfaces at night.
- model
- A simple representation of a real process.
- observe
- To watch carefully.
Summary
- Heat increases evaporation, as shown by water evaporating faster in the sun.
- Steam condenses into droplets on a cold surface, modelling cloud formation and rain.
- Drying clothes, sweat, dew and mist are everyday examples.
Class activity: Evaporation Race
- Set up saucers of water in the sun, the shade and near a fan.
- Record the water level every hour.
- Explain which evaporated fastest and why.
You need: Teacher-handled kettle of hot water, Clear glass plate, Ice cubes
Exercises
Answer in your exercise book first, then check your answers.
1. Droplets on a cold bottle are formed by…
- A. condensation
- B. evaporation
- C. melting
- D. freezing
Show answer
Answer: condensationVapour cools.2. Which saucer of water evaporates fastest?
- A. the one in the sun
- B. the one in the shade
- C. the one in a fridge
- D. they are all the same
Show answer
Answer: the one in the sunHeat.3. Morning dew is an example of condensation.
- A. True
- B. False
Show answer
Answer: TrueCool surfaces.4. Hot water vapour from boiling water is ______.
Show answer
Answer: steamVapour.5. Describe an experiment to show condensation.
Show answer
Answer: Hold a cold plate above steam from a kettle and observe droplets forming and dripping.Experiment.6. How does the condensation experiment model rain?
Show answer
Answer: Vapour condenses into droplets that join and drip, like cloud droplets joining and falling as rain.Model.
Homework
- Observe and record three examples of evaporation and condensation at home.