NCERT Solutions for Class 7 Social Science Geography Chapter 5 Water

The major sources of fresh water are the rivers, ponds, springs and glaciers. The ocean bodies and the seas contain salty water.

When the water on the surface of the ocean rises and falls alternately, they are called waves. During a storm, the winds blowing at very high speed form huge waves. These may cause tremendous destruction.

An earthquake, a volcanic eruption or underwater landslides can shift large amounts of ocean water. As a result, a huge tidal wave called tsunami, that may be as high as 15m., is formed. The largest tsunami ever measured was 150m. high. These waves travel at a speed of more than 700 km. per hour. The tsunami of 2004 caused wide spread damage in the coastal areas of India. The Indira point in the Andaman and Nicobar Islands got submerged after the tsunami.

The rhythmic rise and fall of ocean water twice in a day is called a tide. It is high tide when water covers much of the shore by rising to its highest level. It is low tide when water falls to its lowest level and recedes from the shore.

The strong gravitational pull exerted by the sun and the moon on the earth’s surface causes the tides. The water of the earth closer to the moon gets pulled under the influence of the moon’s gravitational force and causes high tide. During the full moon and new moon days, the sun, the moon and the earth are in the same line and the tides are highest. These tides are called spring tides.

When the moon is in its first and last quarter, the ocean waters get drawn in diagonally opposite directions by the gravitational pull of sun and moon resulting in low tides. These tides are called neap tides.

Ocean currents are streams of water flowing constantly on the ocean surface in definite directions. The ocean currents may be warm or cold. Generally, the warm ocean currents originate near the equator and move towards the poles. The cold currents carry water from polar or higher latitudes to tropical or lower latitudes.

Precipitation is the deposition of moisture from the atmosphere onto the earth’s surface. This may be in form of rain, hail, frost, fog, sleet or snow.

The process by which water continually changes its form and circulates between oceans, atmosphere and land is known as the water cycle.

Factors affecting the height of the waves: Speed off wind Duration of wind Distance the wind blows over water Earthquake Volcanic Eruption Underwater Landslides.

Factors affecting the movement of ocean water: Temperature Earthquake or volcanic eruption Gravitational pull of the sun and the moon Underwater landslides Rotation of the earth.

The rhythmic rise and fall of ocean water twice a day is called a tide. Tides are caused due to the gravitational pull exerted by the sun and the moon on the earth’s surface.

Ocean currents are streams of water flowing constantly on the ocean surface in definite directions.

Ocean water is salty because it contains large amount of dissolved salts. Most of the salt is sodium chloride or the common table salt that we eat.

The quality of water is deteriorating because: Garbage we throw in the river. Chemicals polluted water from industries. Remains of the harmful insecticides and pest resistant’s flowing in from the fields. Unburnt or half burnt corpses of men and animals thrown in water bodies.

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