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Year 7 Science — Earth & Space

The Water Cycle and Weather

Explore how water moves through Earth's systems, understand the processes that drive the water cycle, and learn about clouds and weather patterns.

The Water Cycle

The water cycle (also called the hydrological cycle) is the continuous movement of water through Earth's systems — the atmosphere, lithosphere (land), hydrosphere (oceans, rivers, lakes), and biosphere (living things). Water changes state as it cycles between these reservoirs.

The water cycle is driven primarily by solar energy (heat from the Sun) and gravity. There is no start or end — it is a continuous cycle.

Water Cycle Diagram

Sun Ocean Lake Evaporation Transpiration Condensation (vapour → cloud droplets) Precipitation Collection (runoff into rivers, lakes, ocean) Infiltration (into groundwater)

Key Processes of the Water Cycle

1. Evaporation

Water changes from a liquid to a gas (water vapour) when heated by the Sun. This occurs from oceans, lakes, rivers, and wet surfaces. Transpiration is a related process where water evaporates from the leaves of plants through tiny pores called stomata.

2. Condensation

As warm, moist air rises and cools, water vapour changes from a gas back into tiny liquid droplets. These droplets form around tiny particles (dust, pollen) called condensation nuclei, creating clouds.

3. Precipitation

When cloud droplets combine and become too heavy to remain suspended in the atmosphere, they fall to Earth as precipitation. This can take the form of rain, snow, sleet, or hail, depending on temperature conditions.

4. Collection (Runoff & Infiltration)

Precipitation collects in oceans, rivers, lakes, and reservoirs (surface runoff), or soaks into the ground (infiltration) to become groundwater. Groundwater can eventually flow back to the surface through springs or be absorbed by plant roots.

Cloud Types and Formation

Clouds form when moist air rises, cools to its dew point, and water vapour condenses around tiny particles. Cloud types are classified by their altitude and shape.

Cloud Altitude Chart

10+ km 6 km 2 km Ground Altitude HIGH Cirrus Thin, wispy, ice crystals Cirrocumulus Small white puffs MIDDLE Altostratus Grey sheet, covers sky Altocumulus White/grey puffy patches LOW Cumulus Fluffy, fair weather Stratus Flat, grey, overcast Cumulonimbus Tall, thunderstorms

Weather vs Climate

Weather

  • Short-term atmospheric conditions
  • Changes day to day or even hour to hour
  • Includes temperature, rainfall, wind, humidity, cloud cover
  • Example: "It is 28 °C and sunny today in Sydney"

Climate

  • The average weather conditions over a long period
  • Typically measured over 30+ years
  • Describes what weather is usually like in a region
  • Example: "Sydney has a warm, temperate climate"

Memory aid: "Climate is what you expect; weather is what you get."

Key Vocabulary

Evaporation

The process where liquid water changes to water vapour (gas) due to heating. Occurs at the surface of a liquid below its boiling point.

Condensation

The process where water vapour (gas) cools and changes back into liquid water droplets. Forms clouds.

Transpiration

The release of water vapour from plants through their stomata (tiny pores on leaves).

Precipitation

Water that falls from clouds to the ground as rain, snow, sleet, or hail.

Groundwater

Water that has infiltrated into the soil and rock below the surface. Stored in aquifers.

Dew Point

The temperature at which air becomes saturated and water vapour begins to condense into liquid.

Worked Examples

1

Explain how a puddle disappears on a sunny day.

Step 1: The Sun provides thermal energy (heat) to the puddle.

Step 2: This energy causes water molecules at the surface to gain enough kinetic energy to escape as water vapour (gas).

Answer: The puddle disappears through evaporation. Heat from the Sun converts the liquid water into water vapour, which rises into the atmosphere.

2

Describe how clouds form.

Step 1: Warm, moist air rises from the surface (because warm air is less dense).

Step 2: As it rises, the air cools. At a certain altitude, the temperature drops to the dew point.

Step 3: Water vapour condenses around tiny particles (condensation nuclei) to form tiny water droplets.

Answer: Clouds form when warm, moist air rises, cools to its dew point, and the water vapour condenses into tiny droplets around condensation nuclei.

3

A tall, dark cloud is observed. What type is it, and what weather might it bring?

Step 1: Tall, dark clouds that extend to great heights are cumulonimbus clouds.

Step 2: Cumulonimbus clouds are associated with heavy precipitation and severe weather.

Answer: This is a cumulonimbus cloud. It is likely to bring heavy rain, thunderstorms, lightning, and possibly hail.

Knowledge Check

Select the correct answer for each question. Click "Check Answer" to see if you are right.

Question 1

What process changes water vapour (gas) into liquid water droplets?

Question 2

What is the primary energy source that drives the water cycle?

Question 3

Which type of cloud is most likely to produce thunderstorms?

Question 4

What is the difference between weather and climate?

Question 5

Transpiration is the process by which:

Key Concepts Summary

Year 7: Mixtures Separation Year 8: Body Systems