Quick Revision Notes & Formula Sheet

Class: 7th | Subject: Social Science (Geography)

Chapter: Water

### Concept 1: Distribution of Water Bodies on Earth

• Blue Planet: Earth is called the "Blue Planet" because about three-fourths (71%) of its surface is covered with water.
• Water Composition:
  • Ocean Water: 97.3% (Saline / Unfit for human consumption)
  • Ice-caps: 02.0%
  • Groundwater: 0.68%
  • Freshwater Lakes: 0.009%
  • Inland Seas & Salt Lakes: 0.005%
  • Atmosphere: 0.001%
  • Rivers: 0.0001%
• Freshwater Availability: Only about 2.7% of total water is freshwater, and nearly 70% of that is trapped as ice caps and glaciers in Antarctica, Greenland, and mountain peaks. Only 1% is available and fit for human use (as groundwater and surface water).

### Concept 2: The Water Cycle (Hydrological Cycle)

• Definition: The continuous movement of water within the Earth and atmosphere through evaporation, condensation, and precipitation.
• Key Processes:
  1. Evaporation: Sun's heat turns water from oceans, lakes, and rivers into water vapor.
  2. Condensation: Water vapor cools down and changes back into liquid water droplets, forming clouds.
  3. Precipitation: Fall of condensed water in the form of rain, snow, sleet, or hail.
  4. Transpiration: Release of water vapor by plants through leaves.

### Concept 3: Movements of Ocean Water

Unlike calm inland water, ocean water is constantly moving. It is divided into three main movements:

1. Waves:

   • Definition: The alternate rise and fall of water on the surface of the ocean.
   • Cause: Winds push the water surface. Stronger winds cause bigger waves.
   • Tsunami: A huge tidal wave caused by underwater earthquakes or volcanic eruptions.

2. Tides:

   • Definition: The rhythmic rise and fall of ocean water twice in a day.
   • Cause: The gravitational pull exerted by the sun and the moon on the earth's surface.
   • Types of Tides:
     • Spring Tides: When the moon, sun, and earth are in the same line (during Full Moon and New Moon), tides are highest.
     • Neap Tides: When the moon is in its first and last quarter, ocean waters are drawn diagonally in opposite directions by the gravitational pull of sun and earth, resulting in low tides.
   • Importance of Tides: Help in navigation, fishing, and generating electricity (tidal energy).

3. Ocean Currents:

   • Definition: Streams of water flowing constantly on the ocean surface in definite directions.
   • Types:
     • Warm Currents: Originate near the equator and move towards the poles (e.g., Gulf Stream).
     • Cold Currents: Carry water from polar or higher latitudes to tropical or lower latitudes (e.g., Labrador Current).
   • Fishing Grounds: Areas where warm and cold currents meet provide the best fishing grounds in the world (e.g., areas around Japan and eastern coast of North America).

### Important Key Terms & Definitions (महصूर शब्द)

• Salinity: The amount of salt in grams present in 1000 grams of water. The average salinity of the oceans is 35 parts per thousand.
• Dead Sea: Located in Israel, it has a salinity of 340 grams per litre of water, which makes swimmers float because the increased salt content makes it dense.
• Tsunami: A Japanese word meaning "Harbour waves" as harbours get destroyed whenever there is a tsunami.
• Freshwater (शुद्ध जल): Water that is potable (fit for drinking) and has low salt content.