Air and wind
We cannot see air, yet a flapping flag, a flying kite and our own breathing show that it is there.
Air is a mixture of gases, mainly nitrogen and oxygen, with a little carbon dioxide and water vapour. Living things need the oxygen in it. Wind is moving air. We use it for windmills, sailing, flying kites and drying clothes.
In the figure: Wind turns windmills and pushes sails.
Rule 1: What air contains — Air is a mixture, not one gas.
- Easy: About four-fifths is nitrogen and one-fifth oxygen.
- Medium: Plants use carbon dioxide; animals use oxygen.
- Exam-type: Moving air also carries seeds, smells and sound.
Rule 2: Uses of wind — Wind is a free source of energy.
- Easy: Wind turbines make electricity.
- Medium: Sailing boats use wind to move.
- Exam-type: Wind helps farmers to winnow grain.
Never call air "empty"; it is a mixture that takes up space.
Thinking air is only oxygen.
"Air: mixture; wind: air in motion."
Practice questions
- 1Which gas in the air do our bodies need to perform their functions?
- 2Which gas forms the largest part of air?
- 3About what percentage of air is oxygen?
- 4Nitrogen forms about what percentage of air?
- 5Which sign tells us air is present?
- 6Argon, carbon dioxide and other gases together make up about —
- 7When wind blows gently it is called a —
- 8Wind rotates the wings of a windmill, which can be used to —
Show answers (try them yourself first)
- 1Oxygen
- 2Nitrogen
- 321%
- 478%
- 5Leaves of a tree rustle
- 61% of air
- 7breeze
- 8generate electricity or pull up water
Water: uses, wastage and conservation
A tap left dripping all night fills a bucket by morning; that is water nobody drank.
We use water for drinking, cooking, washing, farming and industry. Most of Earth's water is salty sea water; only a small part is fresh. So we must conserve it: mend leaks, close taps, reuse water and practise rainwater harvesting.
In the figure: Only a small share of water is fresh, so each drop counts.
Rule 1: Uses and wastage — Notice where water is wasted.
- Easy: Farms use the most water.
- Medium: A running tap while brushing wastes litres.
- Exam-type: Leaking pipes waste water silently.
Rule 2: Saving water — Small habits add up.
- Easy: Use a bucket instead of a shower or hose.
- Medium: Water plants with leftover washing water.
- Exam-type: Collect rainwater from roofs and store it.
Check taps at home for leaks and report them.
Believing sea water can be used directly to drink.
"Fix, shut, reuse, harvest."
Practice questions
- 1Water covers about what fraction of the Earth's surface?
- 2Which is a source of freshwater?
- 3Most of the water on Earth is found in —
- 4Fixing water leakages helps to —
- 5Stepwells are commonly known as Bawadi in Rajasthan and as —
- 6Ocean water is not fit for domestic, agricultural and industrial use because it is —
- 7For domestic, agricultural and industrial use we need —
- 8Freshwater in ice sheets or underground is —
Show answers (try them yourself first)
- 1two-thirds
- 2Rivers and lakes
- 3oceans and seas
- 4reduce wastage of water
- 5Vav in Gujarat
- 6saline (salty)
- 7freshwater
- 8difficult to access
Water: uses, wastage and conservation
In the app you can move this figure with your finger.
Open in the appEnergy from the Sun and forests
A cloth dries faster in sunshine, and a village cooks on firewood from nearby trees.
The Sun gives solar energy as light and heat, used in solar cookers, water heaters and solar panels that make electricity. Forests give wood for fuel, food, medicines and raw material, and their trees give oxygen and hold the soil. Cutting forests carelessly harms all of this.
In the figure: A solar panel turns sunlight into electricity; forests give many things.
Rule 1: Solar energy — Sunshine is free and does not run out.
- Easy: Solar cookers boil and bake food with sunlight.
- Medium: Solar panels light street lamps.
- Exam-type: They work best on clear sunny days.
Rule 2: Forests — Forests are the lungs and larder of nature.
- Easy: Forests give wood, fruits, honey and medicines.
- Medium: Tree roots stop soil from washing away.
- Exam-type: Plant a tree for every tree that is cut.
Name one thing in your home made from forest produce.
Believing solar panels work at night.
"Sun: light and heat. Forest: wood, food, air."
Practice questions
- 1The main source of energy on Earth is the —
- 2Plants use sunlight to —
- 3Energy from the Sun is used directly in a —
- 4Forests are large areas with —
- 5Van Mahotsav is a forest festival celebrated during —
- 6In the conversation about the grazing cow, the statement that the cow gets energy from the Sun is correct because —
- 7Solar panels capture the Sun's energy and produce —
- 8A solar water heater uses the Sun's energy to —
Show answers (try them yourself first)
- 1Sun
- 2prepare food
- 3solar cooker
- 4dense growth of various types of plants
- 5July
- 6grass needs sunlight to grow
- 7electricity
- 8heat water
Soil, rocks, minerals and fossil fuels
The soil we grow crops in was once rock, and the coal in a power plant was once a forest.
Soil forms slowly as rocks break up and plant and animal remains decay. We use it for crops, pots and bricks. Rocks give building stone, and minerals are dug from mines for metals. Fossil fuels - coal, petroleum and natural gas - formed over millions of years from dead plants and animals.
In the figure: Ground layers: soil on top, rocks below, fossil fuels deep underground.
Rule 1: Soil, rocks, minerals — Each has its own uses.
- Easy: Soil grows crops; clay makes pots and bricks.
- Medium: Granite and marble are used to build.
- Exam-type: Iron ore from mines gives steel.
Rule 2: Fossil fuels — They took millions of years to form.
- Easy: Coal makes electricity and runs factories.
- Medium: Petroleum gives petrol, diesel and LPG.
- Exam-type: They cannot be made again quickly; burning them makes smoke.
Remember that soil takes hundreds of years to form, so protect it.
Thinking fossil fuels will never run out.
"Soil from rock; fossil fuels from old life."
Practice questions
- 1Which rock is used for roofing?
- 2How long do fossil fuels take to form?
- 3Soil is formed by the disintegration of —
- 4Soil is formed over —
- 5After touching soil collected from different places, we should —
- 6Important rocks include granite, sandstone and —
- 7A mobile phone contains about a dozen minerals like —
- 8Which of these helps in turning and loosening the soil?
Show answers (try them yourself first)
- 1Slate
- 2millions of years
- 3rocks
- 4thousands of years
- 5wash our hands thoroughly
- 6marble
- 7gold, silver, copper and cobalt
- 8Earthworms
Soil, rocks, minerals and fossil fuels
In the app you can move this figure with your finger.
Open in the appNatural resources: renewable and non-renewable
A well refills after rain, but a coal mine, once emptied, does not fill again.
Things nature gives us are natural resources. Renewable resources like sunlight, wind and water are replaced again and again. Non-renewable resources like coal, petroleum and minerals are limited. We should reduce, reuse and recycle to make them last.
In the figure: Renewable ones return; non-renewable ones are limited.
Rule 1: Two kinds — Ask: will it be replaced in our lifetime?
- Easy: Sunlight, wind, rivers: renewable.
- Medium: Coal, petroleum, natural gas: non-renewable.
- Exam-type: Forests are renewable only if we replant.
Rule 2: Using wisely — Make resources last for the future.
- Easy: Reduce: switch off lights and fans not in use.
- Medium: Reuse: use a cloth bag again and again.
- Exam-type: Recycle: send paper, glass and metal for recycling.
For any resource ask: does it get replaced, and how fast?
Calling all resources renewable because nature keeps making them.
"Renewable returns; non-renewable ends; 3R."
Practice questions
- 1Which is an example of a renewable resource?
- 2Resources we get from nature are called —
- 3Resources created by human beings are called —
- 4Resources that get renewed within a reasonable period are called —
- 5Resources found in limited quantities that are not replenished in a reasonable time are called —
- 6Minerals are —
- 7Which of these is a human-made resource?
- 8Which of these is a natural resource?
Show answers (try them yourself first)
- 1Water
- 2natural resources
- 3human-made resources
- 4renewable resources
- 5non-renewable resources
- 6non-renewable resources
- 7Electric bulb
- 8Air