make a story on the basis of air , winds and cyclones
Answers
TABLE OF CONTENT
1. AIR EXERTS PRESSURE
2. HIGH SPEED WINDS ARE ACCOMPANIED BY REDUCED AIR PRESSURE
3. AIR EXPANDS ON HEATING
4. WIND CURRENTS ARE GENERATED DUE TO UNEVEN HEATING ON THE EARTH
5. THUNDERSTORMS AND CYCLONES
6. DESTRUCTION CAUSED BY CYCLONES
7. EFFECTIVE SAFETY MEASURES
8. ADVANCED TECHNOLOGY HAS HELPED
KEYWORDS
WHAT YOU HAVE LEARNT
DID YOU KNOW?
EXERCISES
EXTENDED LEARNING - ACTIVITIES AND PROJECTS
Orissa was hit by a cyclone with wind speed of 200 km/h on 18 October 1999. The cyclone smashed 45,000 houses making 7,00,000 people homeless. On 29 October the same year, a second cyclone with wind speed of 260 km/h hit Orissa again. It was accompanied by water waves about 9 m high. Thousands of people lost their lives. Property worth crores of rupees was destroyed. The cyclone affected agriculture, transport, communication, and electricity supply.
Courtesy: India Meteorological Department, New Delhi
But, what are cyclones? How are they formed? Why are they so destructive? In this chapter we shall seek answers to some of these questions.
We begin with some activities involving air. These activities will clarify some basic features concerning a cyclone. Before we begin, remember that the moving air is called the wind
1. AIR EXERTS PRESSURE
ACTIVITY 8.1
Whenever an activity involves heating, be very careful. It is advised that such activities are performed in the presence of an elderly person from your family. Or, carry out these activities in the presence of your teacher.
You need to boil water in the following activity.
Take a tin can with a lid. Fill it approximately half with water. Heat the can on a candle flame till the water boils. Let the water boil for a few minutes. Blow out the candle. Immediately put the lid tightly on the can. Be careful in handling the hot can. Put the can carefully in a shallow metallic vessel or a washbasin. Pour fresh water over the can. What happens to the shape of the can?
Can you guess why the shape of the can gets distorted?
If you cannot get a tin can, take a soft plastic bottle. Fill it with hot water. Empty the bottle and immediately cap it tightly. Place the bottle under running water.
Recall now some of your experiences.
When you fly a kite, does the wind coming from your back help?
If you are in a boat, is it easier to row it if there is wind coming from behind you?
Do you find it difficult to ride a bicycle against the direction of the wind.
You know that we have to fill air into the bicycle tube to keep it tight. Also, you know that a bicycle tube overfilled with air may burst. What is the air doing inside the tube?
Discuss with your friends how the air in the bicycle tube keeps it in shape.
All these experiences show that the air exerts pressure. It is due to this pressure that the leaves of trees, banners, or flags flutter when the wind is blowing. You can list some more experiences which show that the air has pressure.
Let us now try to explain why the can (or the bottle) gets distorted. As water is poured over the can, some steam in the can condenses into water, reducing the amount of air inside. The pressure of air inside the can decreases than the pressure exerted by the air from outside the can. As a result the can gets compressed.
This activity again confirms that air exerts pressure.