Chapter 5: Water
Overview of the Chapter
Understanding the Chapter
This chapter covers the distribution of water on Earth, the water cycle, and the various movements within ocean bodies including waves, tides, and currents. It emphasizes the importance of water and the need for its conservation.
Distribution of Water on Earth
Major Sources
Oceans: Contain 97.3% of the Earth’s water, which is saline.
Freshwater: Makes up only 2.7% of the Earth’s water, found in rivers, ponds, springs, glaciers, ice caps, and groundwater.
Distribution:
Icecaps and Glaciers: 2.0%
Groundwater: 0.68%
Freshwater Lakes: 0.009%
Inland Seas and Salt Lakes: 0.009%
Atmosphere: 0.0019%
Rivers: 0.0001%
The Water Cycle
Process and Importance
Evaporation: Sun’s heat causes water from oceans, rivers, and lakes to evaporate and form water vapor.
Condensation: Water vapor cools and forms clouds.
Precipitation: Water falls back to Earth as rain, snow, sleet, or hail.
Collection: Water collects in rivers, lakes, and oceans, and the cycle continues.
Ocean Movements
Waves
Formation: Caused by wind blowing across the water surface.
Characteristics: Alternate rise and fall of ocean water.
Impact: Can cause coastal erosion and formation of beaches.
Tides
Definition: The rhythmic rise and fall of ocean water twice a day.
Causes: Gravitational pull of the moon and the sun.
Types:
Spring Tides: Occur during full and new moon when the sun, moon, and Earth are in a straight line, resulting in higher high tides.
Neap Tides: Occur during the first and last quarter moon when the sun and moon are at right angles to each other, resulting in lower high tides.
Importance: Aid in navigation, fishing, and can be used to generate electricity.
Ocean Currents
Definition: Continuous, directed movement of seawater.
Types:
Warm Currents: Originate near the equator and move towards the poles. Example: Gulf Stream.
Cold Currents: Originate in polar regions and move towards the equator. Example: Labrador Current.
Effects:
Influence climate and weather patterns.
Create rich fishing grounds where warm and cold currents meet.
Importance of Water
Essential for Life
Human Use: Drinking, agriculture, industry, and domestic purposes.
Ecosystems: Supports aquatic life and terrestrial ecosystems.
Conservation of Water
Need for Conservation
Scarcity: Limited availability of freshwater.
Pollution: Freshwater resources are being polluted by industrial waste, agricultural runoff, and domestic sewage.
Sustainable Use: Importance of using water judiciously to ensure its availability for future generations.
Conclusion
Summary of the Chapter
Water is a vital resource that covers 71% of the Earth’s surface.
The water cycle is crucial for maintaining life and ecological balance.
Ocean movements such as waves, tides, and currents play significant roles in shaping the Earth’s coastlines and affecting global climates.
Conservation of water is essential to address scarcity and ensure sustainable use.
Additional Information
Key Terms and Concepts
Water Cycle: The continuous movement of water on, above, and below the surface of the Earth.
Evaporation: The process by which water changes from a liquid to a gas.
Condensation: The process by which water vapor changes back to liquid.
Precipitation: Any form of water that falls from clouds and reaches the ground.
Waves, Tides, and Currents: Movements of ocean water that influence marine and coastal environments.
Important Examples and Places
Gulf Stream: A warm ocean current affecting the climate of the east coast of North America and western Europe.
Labrador Current: A cold ocean current that affects the climate of northeastern North America.
Notable Facts
Tsunamis: Large sea waves caused by underwater earthquakes, volcanic eruptions, or landslides.
Spring Tides and Neap Tides: Variations in tidal heights due to the relative positions of the Earth, moon, and sun.
Frequently Asked Questions (FAQs)
97.3% of the Earth’s water is found in oceans.
The main sources of freshwater are rivers, ponds, springs, glaciers, and groundwater.
The water cycle.
Evaporation, condensation, precipitation, and collection.
The sun’s heat causes evaporation.
Water vapor cools and forms clouds.
Precipitation is when water falls back to Earth as rain, snow, sleet, or hail.
Waves, tides, and currents.
Wind blowing across the water surface.
Tides are the rhythmic rise and fall of ocean water, caused by the gravitational pull of the moon and the sun.
Spring tides occur during full and new moons with higher high tides, while neap tides occur during the first and last quarter moons with lower high tides.
A tsunami is a huge tidal wave caused by an underwater earthquake, volcanic eruption, or landslide.
Ocean currents are continuous, directed movements of seawater classified as warm currents and cold currents.
The Gulf Stream.
The Labrador Current.
Water is essential for drinking, agriculture, industry, and supporting ecosystems.
Overuse, pollution, and unequal distribution of water resources.
Through industrial waste, agricultural runoff, and domestic sewage.
Rainwater harvesting, recycling water, fixing leaks, and using watersaving devices.
Glaciers store freshwater and release it through melting.
Groundwater is water found underground in aquifers and is crucial for drinking and irrigation.
Human activities like deforestation, urbanization, and pollution disrupt the natural water cycle.
Oceans absorb and store solar energy, distribute heat around the globe, and influence weather patterns.
Desalination is the process of removing salt from seawater to make it potable, crucial for waterscarce regions.
Climate change can lead to altered precipitation patterns, more frequent droughts, and melting glaciers, affecting water availability.
Chapter 5: Water MCQs
1. What percentage of the Earth’s water is found in oceans?
2. Which process is responsible for water changing from liquid to vapor in the water cycle?
3. What is the primary source of freshwater on Earth?
4. Which layer of the atmosphere contains the ozone layer?
5. What causes tides in the oceans?
6. What is a tsunami?
7. What are the two main types of ocean currents?
8. Why is the conservation of water important?
9. What is the process of removing salt from seawater to make it potable called?
10. Which type of rainfall is caused by air rising over mountains?
11. Which ocean current is an example of a warm current?
12. What is the primary cause of water pollution?
Access detailed short notes for all chapters of the Class 7 History NCERT book ‘Our Pasts-II,’ perfect for CBSE students. Click here to view the complete collection.
