Water is an essential part of our daily lives, appearing in rivers, rainfall, and even the taps we use. This chapter explores the journey of water, beginning with a simple question—where does it go when puddles dry up? The concept of the water cycle is introduced, explaining key processes like evaporation, condensation, and precipitation. Water continuously changes form and moves across the planet. The chapter also emphasizes how Earth’s water has been circulating for millions of years, traveling across vast distances without ever truly disappearing.
1. Introduction to Water
- What We Think of Water:
- Rivers flowing, waterfalls dropping, rain falling softly, and water coming from taps.
- Kids enjoy floating paper boats in puddles after rain, but puddles disappear by noon.
- Where Water Goes:
- Sun heats water, turning it into vapour (evaporation).
- Vapour cools, forms clouds (condensation), and falls as rain, snow, or sleet.
2. Water Cycle
- Definition:
- The way water keeps changing its form and moving between oceans, air, and land.
- Facts:
- Earth works like a closed box—same water from hundreds of years ago is still here.
- Water irrigating fields in Haryana today might have been in the Amazon River long ago.
3. Sources of Water
- Fresh Water Sources:
- Rivers, ponds, springs, and glaciers give us fresh water we can use.
- Salty Water Sources:
- Oceans and seas have salty water because of dissolved salts, mostly sodium chloride (table salt).
- Salinity Facts:
- Salinity means grams of salt in 1000 grams of water.
- Oceans have 35 grams of salt per 1000 grams on average.
- Dead Sea in Israel has 340 grams per litre, so swimmers float easily due to high salt making it dense.
4. Distribution of Water Bodies
- Earth’s Water:
- Three-fourths of Earth is covered with water.
- Why Water Scarcity Happens:
- Not all water is usable; lots of it is salty or locked away.
- Water Distribution:
- Oceans: 97.3% (salty water).
- Ice-caps: 2.0% (frozen fresh water).
- Ground water: 0.68% (under the ground).
- Fresh water lakes: 0.009% (small amount).
- Inland seas and salt lakes: 0.009% (salty).
- Atmosphere: 0.0019% (vapour in air).
- Rivers: 0.0001% (tiny part).
- Key Point:
- Most water is salty or not easy to get, so we must not waste the little fresh water we have.
5. Importance of Water
- Why Water Matters:
- We need it to live; it quenches thirst like nothing else.
- Conservation Need:
- Wasting water is throwing away something very precious.
6. Ocean Circulation
- Ocean Movements:
- Ocean water never stops moving, unlike calm ponds and lakes.
- Types of Movements:
- Waves, tides, and currents keep the ocean alive and active.
7. Waves
- Definition:
- Water on the ocean surface going up and down.
- Examples:
- A ball thrown into the sea gets pushed back to shore by waves.
- During Storms:
- Strong winds make huge waves that can destroy things.
- Tsunami:
- Big waves from earthquakes, volcanoes, or landslides under the sea.
- Can be 15 metres high, with the biggest ever at 150 metres.
- Travel over 700 km per hour.
- Example: 2004 tsunami damaged India’s coastal areas, sinking Indira Point in Andaman and Nicobar.
8. Tsunami – Earth’s Big Trouble
- What Happened in 2004:
- On 26 December 2004, a tsunami hit the Indian Ocean.
- Cause:
- Earthquake near Sumatra (9.0 on Richter scale) moved the sea floor 10-20 metres.
- Indian plate went under Burma plate, shifting water.
- How It Moved:
- Water pulled back from coasts, then rushed in at 800 km per hour.
- Waves slowed to 70 km per hour near land but went 3 km inland.
- Damage:
- Killed over 10,000 people, wrecked more than a lakh houses.
- Worst hit in India: Andhra Pradesh, Tamil Nadu, Kerala, Puducherry, Andaman and Nicobar.
- Indira Point got fully submerged.
- Facts:
- Pacific Ocean has warning systems, but Indian Ocean doesn’t because tsunamis are rare here.
- People didn’t know to run; many watched the water pull back and got caught by the wave.
9. Tides
- Definition:
- Ocean water rising and falling twice daily.
- High tide: Water reaches the shore’s highest point.
- Low tide: Water drops to its lowest and moves back.
- Cause:
- Sun and moon pull on Earth’s water with gravity.
- Moon’s pull makes high tides where water is closest to it.
- Types:
- Spring Tides: Biggest tides when sun, moon, and Earth line up (full moon and new moon).
- Neap Tides: Smaller tides when sun and moon pull in opposite ways (first and last quarter moon).
- Uses:
- High tides help ships reach harbours.
- Bring more fish near shore for fishermen.
- Used to make electricity in some places.
10. Ocean Currents
- Definition:
- Streams of water moving in set paths on the ocean surface.
- Types:
- Warm Currents: Start near the equator and go to the poles (e.g., Gulf Stream).
- Cold Currents: Bring cold water from poles to warmer areas (e.g., Labrador Current).
- Effects:
- Warm currents make land nearby warmer.
- Where warm and cold currents meet, you get great fishing spots (like seas near Japan and eastern North America).
- These spots can also have foggy weather, making it tough for ships.
11. Questions and Answers
11.1 Short Answer Questions
- What is precipitation?
- Water falling from clouds as rain, snow, or sleet.
- What is water cycle?
- Water changing forms and moving between oceans, air, and land all the time.
- What affects the height of waves?
- Wind speed, earthquakes, volcanoes, and underwater landslides.
- Which factors affect ocean water movement?
- Waves, tides, and currents.
- What are tides and how are they caused?
- Tides are water rising and falling twice a day, caused by the sun and moon’s gravity pulling on Earth.
- What are ocean currents?
- Streams of water flowing in fixed directions on the ocean surface.
11.2 Give Reasons
- Ocean water is salty.
- It has lots of dissolved salts, like sodium chloride, from land washing into it over time.
- The quality of water is getting worse.
- People waste it and pollute it, making less good water available.
11.3 Multiple Choice Questions
- The process where water keeps changing and moving between oceans, air, and land is:
- (a) Water cycle.
- Warm ocean currents usually start near:
- (b) Equator.
- The rhythmic rise and fall of ocean water twice a day is called:
- (a) Tide.
11.4 Matching
- (i) Caspian Sea → (a) Largest lake
- (ii) Tide → (b) Periodic rise and fall of water
- (iii) Tsunami → (c) Strong seismic waves
- (iv) Ocean currents → (d) Streams of water moving along definite paths
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