Water Cycle

Glossary:

• Condensation: The process by which water vapor in the air is changed into liquid water. It is responsible for the formation of clouds.
• Precipitation: Water released from clouds in the form of rain, snow, sleet, or hail.
• Runoff: The part of precipitation that flows over the land surface and eventually into rivers, lakes, and oceans.
• Evaporation: The process by which water changes from a liquid to a gas or vapor.

Water Cycle Explanation: When you think of water, what images come to your mind? You think of rivers, waterfalls, the pitter-patter of raindrops, and 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 into vapor. When the water vapor 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 a terrarium. 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 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 amounts of dissolved salts. Most of the salt is sodium chloride, or the common table salt that you eat.

Distribution of Water Bodies

Activity: Fill one-fourth of a big jar with soil and press it well. Put a thin layer of humus on top of it. Plant the largest plants first and then arrange the smaller ones around them. Spray the arrangement with water and close the jar. The water that evaporates from the leaves and soil condenses and falls back in the form of drops of water.

Explanation: We all know that three-fourths of the earth’s 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.

Water is absolutely essential for survival. Water alone can quench our thirst when we are thirsty. Now don’t you think we are wasting a precious resource when we use water carelessly?

Waves

Glossary:

• Waves: When the water on the surface of the ocean rises and falls alternately, they are called waves.

Explanation: 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 washed back to the shore by the waves. Waves are formed when winds scrape across the ocean surface. The stronger the wind blows, the bigger the wave becomes.

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 a 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 widespread damage in the coastal areas of India. The Indira point in the Andaman and Nicobar islands got submerged after the tsunami.

Tides

Glossary:

• Tides: The rhythmic rise and fall of ocean water twice in a day is called a tide.
• Spring Tides: Tides that occur when the sun, the moon, and the earth are in the same line and the tides are highest.
• Neap Tides: Tides that occur when the moon is in its first and last quarter, and the ocean waters get drawn in diagonally opposite directions by the gravitational pull of the sun and moon resulting in low tides.

Explanation: 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. But when the moon is in its first and last quarter, the ocean waters get drawn in diagonally opposite directions by the gravitational pull of the sun and moon, resulting in low tides. These tides are called neap tides (Fig. 5.5).

High tides help in navigation. They raise the water level close to the shores. This helps the ships to arrive at the harbor more easily. The high tides also help in fishing. Many more fish come closer to the shore during the high tide. This enables fishermen to get a plentiful catch. The rise and fall of water due to tides is being used to generate electricity in some places.

Ocean Currents

Glossary:

• Ocean Currents: Streams of water flowing constantly on the ocean surface in definite directions. They can be warm or cold.

Explanation: Ocean currents are streams of water flowing constantly on the ocean surface in definite directions. The ocean currents may be warm or cold (Fig. 5.6). 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. The Labrador Ocean current is a cold current while the Gulf Stream is a warm current. The ocean current influences the temperature conditions of the area. Warm currents bring about warm temperatures over the land surface. The areas where the warm and cold currents meet provide the best fishing grounds of the world. Seas around Japan and the eastern coast of North America are such examples. The areas where a warm and cold current meet also experience foggy weather, making it difficult for navigation.