Learning Objectives
- Students will learn that air is a mixture of gases.
- Students will understand the properties of air.
- Students will know the uses of air in daily life.
- Students will understand what air pollution is, its causes, effects, and how to prevent it.
Let Us Begin!
Can you see air? Can you hold it in your hands? No! But air is all around us. We breathe it in every moment. Without air, no living thing -- humans, animals, or plants -- can survive.
Air is not just one gas. It is a mixture of many gases. Let us learn what air is made of, why it is important, and what happens when it gets dirty.
What Is Air Made Of?
Air is a mixture of several gases. The main gases in air are:
| Gas | Amount in Air | Importance |
|---|
| Nitrogen | About 78% | Makes up the largest part of air; helps plants grow |
| Oxygen | About 21% | We breathe oxygen to stay alive; needed for burning |
| Carbon Dioxide | A very small amount | Used by plants to make food; released when we breathe out |
| Other gases and water vapour | Very small amounts | Water vapour forms clouds and rain |
Air also contains tiny particles of dust and smoke.
Think about it: When a beam of sunlight enters a dark room, you can see tiny dust particles floating in the air!
Properties of Air
Even though we cannot see air, it has many interesting properties:
- Air has no colour -- it is transparent (we can see through it).
- Air has no taste -- we cannot taste it.
- Air has no smell -- pure air is odourless. (Bad smells come from gases or particles mixed in air.)
- Air takes up space -- blow up a balloon and you can see that air fills the space inside it.
- Air has weight -- a blown-up balloon is slightly heavier than an empty one.
- Air is everywhere -- it fills every empty space around us, even inside soil and water.
- Moving air is called wind -- wind can be gentle (breeze) or very strong (storm).
Think about it: Push an empty glass upside down into a bucket of water. The water does not fill the glass completely. Why? Because air inside the glass takes up space!
Uses of Air
- Breathing: All living things need oxygen from air to breathe and stay alive.
- Burning: Fire needs oxygen to burn. Without air, a candle goes out.
- Plants: Plants use carbon dioxide from air to make their food through a process called photosynthesis.
- Wind energy: Moving air (wind) is used to turn windmills and generate electricity.
- Drying clothes: Air helps wet clothes dry on a clothesline.
- Flying kites and sailing boats: Wind pushes kites and fills the sails of boats.
- Spreading seeds: Wind carries seeds of some plants to new places.
What Is Air Pollution?
When harmful gases, smoke, dust, and chemicals mix with the air and make it dirty, it is called air pollution. Polluted air is dangerous for all living things.
Causes of Air Pollution
- Vehicles: Cars, buses, trucks, and auto-rickshaws release smoke from their exhaust pipes.
- Factories: Factories and power plants release harmful gases and smoke from their chimneys.
- Burning waste: Burning garbage, crop stubble, and dry leaves adds smoke to the air.
- Firecrackers: Bursting crackers during festivals releases smoke and harmful chemicals.
- Construction: Building work creates a lot of dust in the air.
- Cutting trees: Fewer trees means less cleaning of the air.
Think about it: In cities like Delhi, air pollution becomes very bad in winter. People sometimes have to wear masks to protect themselves.
Effects of Air Pollution
- Causes breathing problems, coughing, and diseases like asthma.
- Makes eyes burn and water.
- Harms animals and birds.
- Damages plants and crops.
- Polluted air can cause smog (a thick, foggy layer of dirty air) that makes it hard to see.
How to Keep Air Clean
- Plant more trees: Trees take in carbon dioxide and give out oxygen. They are nature's air cleaners.
- Walk, cycle, or use public transport: This reduces the number of vehicles on the road.
- Do not burn waste: Garbage should be disposed of properly, not burned.
- Use less firecrackers: Celebrate festivals in eco-friendly ways.
- Use clean energy: Solar energy and wind energy do not pollute the air.
- Keep surroundings clean: Do not let dust and garbage pile up.
Key Words and Meanings
| Word | Meaning |
|---|
| Mixture | Two or more things combined together |
| Nitrogen | The gas that makes up the largest part (78%) of air |
| Oxygen | The gas we breathe in to stay alive (21% of air) |
| Carbon Dioxide | A gas we breathe out; used by plants to make food |
| Water Vapour | Water in the form of gas present in air |
| Air Pollution | When harmful substances make the air dirty and unsafe |
| Smog | A thick, dirty fog caused by pollution |
| Photosynthesis | The process by which plants use sunlight and carbon dioxide to make food |
Examples from Daily Life
Example 1: Air Takes Up Space
Kavita blew air into a balloon for her brother's birthday party. The balloon became big and round. This shows that air takes up space. When she let go, the air rushed out and the balloon flew around the room!
Example 2: Pollution in the City
Rohan's family lives near a busy road in Bengaluru. Every morning, they see thick smoke coming from buses and trucks. Rohan's mother keeps the windows closed and has placed indoor plants to help clean the air inside their home.
Example 3: Van Mahotsav
During Van Mahotsav (Tree Planting Week) in July, students of Sita's school planted 50 saplings in their neighbourhood. Their teacher explained that more trees mean cleaner air for everyone.
Key Points to Remember
- Air is a mixture of gases: nitrogen (78%), oxygen (21%), carbon dioxide, and others.
- Air has no colour, taste, or smell. It takes up space and has weight.
- Oxygen is needed for breathing and burning. Carbon dioxide is used by plants.
- Air pollution is caused by vehicles, factories, burning waste, and firecrackers.
- Pollution causes breathing problems, smog, and harms all living things.
- Plant trees, walk or cycle, and avoid burning waste to keep air clean.
Practice Questions
A. Fill in the Blanks
- Air is a of many gases.
- The gas we breathe in is called .
- makes up about 78% of air.
- Plants use to make their food.
- Moving air is called .
B. Multiple Choice Questions
- Which gas is most abundant in air?
(a) Oxygen(b) Carbon Dioxide(c) Nitrogen(d) Water Vapour
- Which of these is a cause of air pollution?
(a) Planting trees(b) Cycling to school(c) Burning garbage(d) Drinking water
- What do plants give out that helps us breathe?
(a) Nitrogen(b) Carbon Dioxide(c) Smoke(d) Oxygen
- Air has no:
(a) Weight(b) Colour or taste(c) Space(d) Gases
C. Short Answer Questions
- Name the main gases present in air and their approximate amounts.
- Write any three properties of air.
- List three causes of air pollution and three ways to keep air clean.
Think and Do -- Fun Activity: Air Is Everywhere!
Experiment: Take an empty glass and a bucket of water. Push the glass upside down straight into the water. Now tilt the glass slightly while it is still under water.
| Step | What Did You Observe? |
|---|
| Glass pushed straight down | |
| Glass tilted under water | |
Did you see bubbles when you tilted the glass? Those bubbles are air escaping from the glass!
What does this experiment prove about air? ____________________________________________________