Air, Water, and Weather
1. Properties of Air
AIR is all around us. It is a MIXTURE of gases.
'You cannot SEE air, but you can FEEL it when the wind blows. You can BREATHE it. And without it, nothing could live!'
Composition of Air:
| Gas | Percentage | What It Does |
|---|---|---|
| Nitrogen | 78% | Most of the air — plants need it |
| Oxygen | 21% | We NEED this to breathe |
| Carbon dioxide | 0.04% | Plants use this for photosynthesis |
| Other gases | 1% | Argon, neon, water vapour, etc. |
Properties of Air:
| Property | How to Prove It |
|---|---|
| Air takes up SPACE | Blow up a balloon — the air fills it |
| Air has WEIGHT | A balloon weighs more when inflated |
| Air exerts PRESSURE | Suck on a straw — air pressure pushes liquid up |
| Air can be COMPRESSED | Squeeze an empty plastic bottle — the air inside compresses |
| Air is NEEDED for burning | A candle goes out when covered with a glass |
| Air is needed for BREATHING | Hold your breath — you need air! |
'WIND is MOVING AIR. The faster the air moves, the STRONGER the wind.'
2. Water
Water is essential for ALL life on Earth.
'About 71% of Earth's surface is covered with WATER. But only 3% of that is FRESH water that we can drink!'
Sources of Water:
| Source | Type | Example |
|---|---|---|
| Rain | Fresh | Rainfall |
| Rivers | Fresh | Ganga, Yamuna |
| Lakes | Fresh | Dal Lake, Chilika |
| Ponds | Fresh | Village ponds |
| Wells | Fresh (groundwater) | Hand pumps, tube wells |
| Oceans | Salty | Bay of Bengal, Arabian Sea |
| Glaciers | Fresh (frozen) | Himalayan glaciers |
Uses of Water:
- Drinking and cooking — we need clean water every day.
- Bathing and washing — for hygiene.
- Agriculture — growing crops needs lots of water.
- Industry — factories use water for cooling, cleaning, and making products.
- Transportation — ships travel on water.
- Recreation — swimming, boating, fishing.
3. The Water Cycle
The WATER CYCLE is the continuous movement of water between the Earth and the atmosphere.
'Water is NEVER lost. It keeps moving in a cycle — from the Earth to the sky and back again!'
Steps of the Water Cycle:
| Step | Process | What Happens |
|---|---|---|
| 1 | Evaporation | Sun heats water in oceans, rivers, lakes → water turns into WATER VAPOUR (gas) and rises |
| 2 | Transpiration | Plants release water vapour through their leaves |
| 3 | Condensation | Water vapour rises, cools down, and turns back into TINY WATER DROPLETS → forms CLOUDS |
| 4 | Precipitation | Clouds become heavy → water falls as RAIN, SNOW, or HAIL |
| 5 | Collection | Water collects in oceans, rivers, lakes, and soil → the cycle STARTS AGAIN |
Diagram of the Water Cycle:
☁️ Condensation → Clouds
↗ ↘
Evaporation Precipitation (Rain)
↖ ↙
🌊 Oceans/Rivers ← Collection ← 🌊
'Water from millions of years ago is the SAME water we drink today! The water cycle REUSES water again and again.'
4. Weather
WEATHER is the condition of the ATMOSPHERE at a particular TIME and PLACE.
'Weather changes every day. It can be SUNNY one day and RAINY the next!'
Elements of Weather:
| Element | What It Measures | How We Measure It |
|---|---|---|
| Temperature | How hot or cold it is | Thermometer (°C) |
| Rainfall | How much rain falls | Rain gauge (mm) |
| Wind | Moving air | Wind vane (direction), Anemometer (speed) |
| Humidity | How much water vapour is in the air | Hygrometer |
| Cloud cover | How much of the sky is covered by clouds | Visual observation |
Weather Instruments:
| Instrument | What It Measures |
|---|---|
| Thermometer | Temperature |
| Rain gauge | Amount of rainfall |
| Wind vane | Wind direction |
| Anemometer | Wind speed |
| Barometer | Air pressure |
5. Seasons
SEASONS are LONG periods of weather that repeat every year.
'India has THREE main seasons: Summer, Rainy (Monsoon), and Winter.'
Summer (March to May):
- VERY HOT — temperatures can reach 45°C in some places.
- Dry and sunny.
- Trees have lots of leaves.
- Mangoes and watermelons are in season!
Rainy / Monsoon (June to September):
- HEAVY rainfall.
- Cooler than summer.
- Rivers fill up.
- Farmers plant crops (kharif crops like rice).
Winter (October to February):
- COLD — temperatures can drop to near 0°C in some places.
- Foggy mornings in many parts of India.
- Trees may shed leaves (deciduous trees).
- Warm clothes are needed.
Autumn and Spring (in some regions):
- Autumn: Leaves turn yellow/brown and fall off trees. (October-November)
- Spring: New leaves and flowers bloom. (February-March)
6. Common Mistakes
- Thinking air is nothing: 'Air IS something — it is a mixture of gases. It has weight, takes up space, and is essential for life.'
- Confusing weather and climate: 'WEATHER changes day to day. CLIMATE is the AVERAGE weather over MANY years in a region.'
- Believing the water cycle makes NEW water: 'NO new water is created. The SAME water molecules have been cycling for millions of years!'
- Thinking clouds are made of water vapour: 'Clouds are made of TINY WATER DROPLETS (liquid) or ICE CRYSTALS, NOT water vapour (which is invisible).'
7. Key Facts to Remember
- 'Air is a mixture of gases — 78% nitrogen, 21% oxygen, and small amounts of other gases.'
- 'Air has weight, takes up space, and exerts pressure.'
- 'The WATER CYCLE has four steps: Evaporation, Condensation, Precipitation, and Collection.'
- 'Weather changes daily. Seasons change yearly.'
- 'India has three main seasons: Summer, Monsoon (Rainy), and Winter.'
- 'We measure temperature with a THERMOMETER and rainfall with a RAIN GAUGE.'
8. Self-Test
Q1: What is the most abundant gas in the air? What percentage does it make up?
Q2: List the four steps of the water cycle in order.
Q3: What is the difference between evaporation and condensation?
Q4: Name the three main seasons in India.
Q5: What instrument is used to measure: (a) Temperature (b) Rainfall (c) Wind direction
Q6: Why does a candle go out when covered with a glass?
Q7: What percentage of Earth's water is fresh water?
Q8: What are clouds made of? Are they made of water vapour?
Answers:
A1: Nitrogen — 78% of the air. A2: (1) Evaporation (2) Condensation (3) Precipitation (4) Collection. A3: Evaporation is liquid water turning into WATER VAPOUR (gas) by HEATING. Condensation is water vapour turning into LIQUID water by COOLING. A4: Summer (March-May), Monsoon/Rainy (June-September), Winter (October-February). A5: (a) Thermometer (b) Rain gauge (c) Wind vane. A6: The candle uses up the OXYGEN inside the glass. Without oxygen, burning cannot happen. A7: Only about 3% of Earth's water is fresh water. A8: Clouds are made of TINY WATER DROPLETS (liquid) or ICE CRYSTALS. They are NOT made of water vapour (which is invisible).
