Air, Water and Weather Cycles

A Today you'll learn

Describe the composition of air (nitrogen, oxygen, carbon dioxide, water vapour)
Explain the continuous water cycle: evaporation, condensation, precipitation, and collection
Understand weather patterns, breezes (sea breeze and land breeze), and seasons

B Let's understand

Air and water are in continuous motion around our planet, driving Earth’s weather and climate. Air is a mixture of gases: roughly 78% nitrogen, 21% oxygen, small amounts of carbon dioxide, argon, and water vapour. Warm air is lighter and rises, while cool air is denser and sinks, creating wind and breezes. Along coastlines, unequal heating creates a sea breeze during the day and a land breeze at night. The Water Cycle is the perpetual movement of water on Earth: Solar heat causes evaporation from oceans and lakes into invisible water vapour. As water vapour rises high into cool air, it condenses into water droplets forming clouds. When clouds become saturated and heavy, water falls back to Earth as precipitation (rain, snow, hail), replenishing rivers and groundwater.

C See it step by step

Example 1: Why do clothes dry faster on a hot, windy afternoon?

High solar heat accelerates the rate of evaporation of water from wet fabric.
Blowing wind carries away water vapour rapidly, preventing humidity buildup.
Therefore, clothes dry much quicker on hot, windy days.

Example 2: How does a sea breeze occur during the day?

During the daytime, land heats up much faster than the sea.
Hot air over the land rises, creating a low-pressure area.
Cool, refreshing air over the sea moves inland to take its place, creating a sea breeze.

D Your turn

Which gas makes up approximately 78% of Earth’s atmosphere?

Look back at "Let's understand" above for a clue.

E Ready to practise?

Air is composed of nitrogen (~78%)

Air is composed of nitrogen (~78%), oxygen (~21%), carbon dioxide, and water vapour.

The water cycle consists of evaporation

The water cycle consists of evaporation, condensation, precipitation, and collection.

Key idea 3

Evaporation is water turning into vapour by heat; condensation is vapour turning back to liquid.

Key idea 4

A sea breeze blows from sea to land during the day; a land breeze blows at night.

Precipitation includes rain

Precipitation includes rain, snow, hail, and sleet.

Warm up

1. Name the two most abundant gases present in the air.

2. Define evaporation and condensation in the water cycle.

3. What is precipitation? Give two examples.

Practise

4. Why does sea breeze blow during the daytime along coastlines?

5. Why does a land breeze blow during the night?

6. How are clouds formed in the sky?

Challenge

7. What role does the sun play in driving the water cycle?

8. Why do dew drops form on grass on cool winter mornings?

Download worksheet (PDF)

Question 1: Name the two most abundant gases present in the air.

Answer: Nitrogen (approx. 78%) and Oxygen (approx. 21%).

Question 2: Define evaporation and condensation in the water cycle.

Answer: Evaporation: liquid water changing into water vapour due to heat. Condensation: water vapour cooling into liquid droplets.

Question 3: What is precipitation? Give two examples.

Answer: Water falling from clouds back to Earth; examples: rain, snow, hail.

Question 4: Why does sea breeze blow during the daytime along coastlines?

Answer: Land heats faster than the sea; warm air rises over land, and cool air from the sea blows in.

Question 5: Why does a land breeze blow during the night?

Answer: At night, land cools faster than the sea; warm air rises over the sea, and cool air blows from land to sea.

Question 6: How are clouds formed in the sky?

Answer: Water vapour rises high, cools down, and condenses around microscopic dust particles into tiny droplets.

Question 7: What role does the sun play in driving the water cycle?

Answer: The sun provides thermal energy that heats surface water and powers evaporation.

Question 8: Why do dew drops form on grass on cool winter mornings?

Answer: Warm moist air touches cold grass surfaces at night, causing water vapour to condense directly into dew.