These DAV Class 7 SST Notes and DAV Class 7 SST Chapter 5 Notes – Water Surrounding the Earth hold significant importance as study material for students.
Water Surrounding the Earth Class 7 DAV Notes
→ Water bodies cover about 71% of the earth’s surface. The oceans are the largest reservoirs of water.
→ The earth receives major part of pure water through rainfall. It also receives fresh water through numerous springs and rivers.
→ The water never remains static. It has a cycle which goes on non-stop. What is this water cycle? The Sun’s heat causes evaporation of water vapour. When the water vapour cools down, it condenses droplets of water to form clouds. When these water droplets become too heavy to float in air, they fall down over the earth’s surface in the form of rain, sleet or snow.
→ A major part of water runs off over the earth’s surface forming numerous streams. A small part of rain water percolates inside the earth which forms ground water, a major source of water for plants.
→ Distribution of water is not uniform. Some areas receive heavy rainfall while some other areas receive low rainfall.
→ Ocean water keeps moving continuously. The movements that occur in oceans can be broadly categorised as waves, ocean currents and tides.
→ The waves are the movements in the waterbody where water particles move up and down. The height of the waves depends on the speed of wind and the duration of wind blowing from a particular direction.
→ Ocean currents are of two types- cold currents and warm currents. These are formed due to heating and cooling of the ocean water. The ocean currents play an important role in influencing the climate of the coastal regions of the continents.
→ Tides are caused due to the gravitational puli of the moon and the sun. Tides occur twice a day. When the level of water rises, it is a high tide and when the level fails, it is a low tide.
→ Oceans play an important role in men’s life. They facilitate countries the cheapest transportation of goods. They are a valuable source of food.
→ Tsunami, huge sea waves, causes destruction on a large scale. The tsunami of 2004 crashed into the coastal regions In many parts of the world, washing away people, animals and homes. Government agencies, NGOs, etc. provided relief to the victims by the donation of money, clothes, medicines, beddings, etc.
→ Water Cycle : The process by which water continually changes its form and circulates between oceans, atmosphere and land.
→ Groundwater : The rain water that percolates inside the earth.
→ Wave : The alternate rise and fall of the water on the surface of the ocean,
→ Ocean Current: The continuous movement of a mass of water in a particular direction.
→ Tide : The periodic rise and faii in the level of ocean water.
→ TsunamiA Japanese name which means ‘huge sea waves’.
→ Fishing grounds: An area in the oceans and seas where fish are in plenty and fishing is usually good.
→ Plankton : Microscopic organisms that drift in the upper water of the sea. Most marine creatures depend upon them directly or indirectly for food. Plankton rich zones in the ocean make good fishing grounds.
→ Stream flow : A portion of run off that enters the river valleys to move towards the oceans.
→ Surface run-off : The part of total precipitation that flows over the ground.
→ Transpiration : The transfer of water vapour to the air from plants.