Water

Q20. What is precipitation?

Ans. Precipitation is any type of water that forms in the Earth's atmosphere and then drops onto the surface of the Earth.

Q21. What is water cycle?

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

Q22. What are tides and how are they caused?

Ans. The rhythmic rise and fall of ocean water twice in a day is called a tide. The strong gravitational pull exerted by the sun and the moon on the earth’s surface causes the tides.

Q23. Which factors affect the movement of ocean water?

Ans. Temperature, density and salinity, storm, earthquake, a volcanic eruption or underwater landslides, gravitational pull exerted by the sun and the moon on the earth’s surface.

Q24. Why is our earth like a terrarium?

Ans. 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.

Q25. Write a short note on waves?

Ans. 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.

Q26. What are the factors affecting the height of the waves?

Ans. During a storm, the winds blowing at very high speed form huge waves. 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.

Q27. What are spring and neap tides?

Ans. 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 sun and earth resulting in low tides. These tides are called neap tides.

Q28. Why are tides important to us?

Ans. Tides important to us because:-

                       i.        High tides help in navigation.

                      ii.        They raise the water level close to the shores. This helps the ships to arrive at the harbour more easily.

                     iii.        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.

                     iv.        The rise and fall of water due to tides is being used to generate electricity in some places.

Q29. Three-fourth of the earth surface is covered by water. Give the distribution of water in percentage?

Ans. The following table gives the distribution of water in percentage.