NCERT Grade 7 Science, Chapter 8, Winds, Storms and Cyclones starts by describing the situation during the cyclone which hit Odisha in 1999. The first half of the chapter focuses on the important features related to the cyclone. The following activities are discussed in this regard:
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Air exerts pressure
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High-speed winds accompanied reduced air pressure
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Air expands on heating
Winds, Storms and Cyclones discuss each property of air with the help of activities. The conclusions of these activities provide some very important characteristics of air and its relationship with speed, pressure and temperature of the region in which it blows. The second half of the chapter Winds, Storms and Cyclones talks about wind currents which are generated due to uneven heating on the earth. This topic is explained under two heads:
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Uneven heating between the equator and the poles
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Uneven heating of land and water
The explanation of this part is supplemented with diagrams presenting the situation during summers and winters respectively. Later, the concept of a thunderstorm is taken into consideration. Information about the structure of cyclone and different names of the cyclone are also included in this section. Thereafter, the destructive effects of cyclones are discussed followed by effective safety measures listed pointwise. The chapter ends with an emphasis on the advanced technology that has helped to cope up with hazardous effects of Winds, Storms and Cyclones.
The topics covered in the chapter, Winds, Storms and Cyclones are -
Air Exerts Pressure, High-Speed Winds Are Accompanied by Reduced Air Pressure, Air Expands on Heating, Wind Currents Are Generated Due to Uneven Heating on the Earth, Thunderstorms and Cyclones, Destruction Caused by Cyclones, Effective Safety Measures and Advanced Technology Has Helped
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Question 1:
Fill the missing word in the blank spaces in the following statements:
(a) Wind is ________ air.
(b) Winds are generated due to ________ heating on the earth.
(c) Near the earth’s surface ________ air rises up whereas _______air comes down.
(d) Air moves from a region of __________ pressure to a region of ________ pressure.
Answer:
(a) Wind is moving air.
(b) Winds are generated due to uneven heating on the earth.
(c) Near the earth’s surface warm air rises up whereas cold air comes down.
(d) Air moves from a region of high pressure to a region of low pressure.
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Question 2:
Suggest two methods to find out wind direction at a given place.
Answer:
The following are the two methods to find out the direction of wind.
(i) While flying a kite, air exerts pressure on the kite due to which the kite flies. The direction in which the kite flies is the direction of blowing of wind.
(ii) While riding a bicycle, the direction in which it is difficult to ride is opposite to the direction of the blowing wind.
Therefore, while flying a kite or riding a bicycle, the wind direction at a given place can be determined.
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Question 3:
State two experiences that made you think that air exerts pressure (other than those given in the text).
Answer:
We have experienced that when we blow a balloon, the balloon becomes tight. If we try to fill more air, then the balloon will burst after an extent. This happens because air exerts pressure.
We have also experienced the movement of fringes of windows and doors of our houses when wind blows in a high speed. This also happens because air exerts pressure.
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Question 4:
You want to buy a house. Would you like to buy a house having windows but no ventilators? Explain your answer.
Answer:
A house having windows but no ventilators should not be bought. This is because warm air is lighter than cold air and therefore, it goes up. This warm air can go outside the house mostly through ventilators. If there are no ventilators, then the warm air cannot go outside easily.
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Question 5:
Explain why holes are made in hanging banners and hoardings.
Answer:
Air exerts pressure. Wind blowing in high speed may break or displace many things. If holes are made in hanging banners and hoardings, then air can pass through these holes, which reduces the air pressure exerted on the banners and hoardings. That is why holes are made in hanging banners and hoardings.
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Question 6:
How will you help your neighbours in case cyclone approaches your village/town?
Answer:
In case cyclone approaches, the neighbours should be helped in the following ways.
(i) By helping in moving to cyclone shelters and other safer places.
(ii) By asking them to take necessary steps to shift animals, vehicles and household goods to safer places.
(iii) By calling the emergency services such as police, fire brigade and medical centres when required.
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Question 7:
What planning is required in advance to deal with the situation created by a cyclone?
Answer:
The following planning is required to deal with the situation created by a cyclone.
(i) Facilities for cyclone prediction and forecasting which can give cyclone warning in advance.
(ii) Quick information and communication linkages so that information can be spread quickly.
(iii) Construction of cyclone shelters and arrangement for moving people to safer places for safety during cyclone.
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Question 8:
Which of the following places is unlikely to be affected by a cyclone?
(i) Chennai (ii) Mangaluru (Mangalore)
(iii) Amritsar (iv) Puri
Answer:
(iii) Amritsar
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Question 9:
Which of the statements given below is correct?
(i) In winter the winds flow from the land to the ocean.
(ii) In summer the winds flow from the land towards the ocean.
(iii) A cyclone is formed by a very high-pressure system with very high-speed winds revolving around it.
(iv) The coastline of India is not vulnerable to cyclones.
Answer:
(i) Correct
In winter the winds flow from the land to the ocean. This is called land breeze.
(ii) Not Correct
In summer the winds flow from the ocean towards the land. This is called sea breeze.
(iii) Not Correct
A cyclone is formed by a very low-pressure system with very high-speed winds revolving around it. The low-pressure region is called the eye of the cyclone.
(iv) Not Correct
The coastline of India is very vulnerable to cyclones.
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