NCERT Book Class 7 Geography Water

Water

When you think of water, what images come to your mind? You think of rivers, the waterfalls, the pitter patter of raindrops, water in your taps... Children love to float paper boats in rain puddles. By noon the puddles vanish. Where does the water go?

The sun’s heat causes evaporation of water vapour. When the water vapour cools down, it condenses and forms clouds. From there it may fall on the land or sea in the form of rain, snow or sleet. The process by which water continually changes its form and circulates between oceans, atmosphere and land is known as the water cycle (Fig 5.1). 

Our earth is like aterrarium. The same water that existed centuries ago still exists today. The water used to irrigate a field in Haryana may have flowed down the Amazon River a hundred years ago. The major sources of fresh water are the rivers, ponds, springs and glaciers. The ocean bodies and the seas contain salty water. The water of the oceans is salty or saline as it contains large

DISTRIBUTION OF WATER BODIES

We all know that three-fourth of the earth surface is covered by water. If there is more water than land on this earth, why do so many countries face water scarcity? Is all the water on earth available to us? The following table gives the distribution of water in percentage.

OCEAN CIRCULATION

There is something magical about walking bare feet on the seashore. The wet sand on the beach, the cool breeze, the seabirds, the smell of the salt in the air and music of the waves; everything is so fascinating. Unlike the calm waters of ponds and lakes, ocean waterkeeps moving continuously. It is never still. The movements that occur in oceans can be broadly categorised as: waves, tides and currents.

Waves

When you are playing throw ball on the beach and the ball falls into the water, what happens? It is fun to watch how the ball gets washedback to the shore by the waves. When the water on the surface of the ocean rises andfalls alternately, they are called waves. Do you know?

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 ofIndia. The Indira point in the Andaman and Nicobar islands got submerged after the tsunami.

Exercises

1. Answer the following questions.

(i) What is precipitation?

(ii) What is water cycle?

(iii) What are the factors affecting the height of the waves?

(iv) Which factors affect the movement of ocean water?

(v) What are tides and how are they caused?

(vi) What are ocean currents?

2. Give reasons.

(i) Ocean water is salty.

(ii) The quality of water is deterioting

3. Tick the correct answer.

(i) The process by which water continually changes its form and circulates between oceans, atmosphere and land

(a) Water cycle   (b) Tides    (c) Ocean currents

(ii) Generally the warm ocean currents originate near

(a) Poles    (b) Equator    (c) None of these

(iii) The rythmic rise and fall of ocean water twice in a day is called

(a) Tide     (b) Ocean current    (c) Wave

Please refer to attached file for NCERT Class 7 Geography Water