Wednesday, December 19, 2012

CBSE Class 7 - Science - CH8 - Winds, Storms and Cyclones

Winds, Storms and Cyclones
Cyclone Hit at Samoa Islands
credits: NOAA

NCERT Solutions, Q & A

Q1: 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.
(e) Air around us exerts __________ in all directions.
(f) Winds carrying ______________ bring rain.
(g) Air _________ on heating while ________ on cooling.
(h) A cyclone is called a __________ in the American continents and __________ in Japan and Philippines.
(i) The word monsoon is derived from the Arabic word _________, which means ‘season’.

(a) moving
(b) uneven
(c) warm, cooler

(d) high, low
(e) pressure
(f)  water from oceans/rivers
(g) expands, contracts
(h) hurricane, typhoon
(i) mausam

Q2: What happens to the pressure of the wind if its speed is increased?

Answer: When the speed of the wind is increases, it reduces the pressure of nearby region.

Q3: Name the instrument used to measure the speed of wind.

Answer: Anemometer.

Q4: Suggest two methods to find out wind direction at a given place.

Answer: The methods are:
  1. Take some fine chalk dust or sand in your hand and slowly slip it off. Movement of dust particles in a particular direction will give the direction of wind flowing.
  2. Fly a kite. In the direction the kite flies shall be the wind direction.
  3. Take small paper piece of paper on your palm. The pieces will fly in the direction of wind is blowing.
  4. Use anemometer or wind wane.

Q5(MCQ):   Air exerts pressure in

(a) all directions
(b) upward direction only
(c) downward direction only
(d) sideways only

Answer: (a) all directions

Q6: State two experiences that made you think that air exerts pressure
(other than those given in the text).

Answer: We experience air pressure in our daily activities such as:
  • Flags and tree leaves flutter due to pressure exerted by air in the form of wind.
  • It is difficult to ride a bicycle against the wind but it is much easier in the direction of wind.

Q7: You want to buy a house. Would you like to buy a house having windows but no ventilators? Explain your answer.

Answer: Fresh air can enter into the house through windows but the warm air and smoke would not go out. Smoke from kitchen and warm air being lighter rise up. If there is no outlet like ventilators, warm air will heat up the room and could cause suffocation and discomfort. 

Q8: Explain why holes are made in hanging banners and hoardings.

Answer: Air exerts pressure in all directions. If banners and hoardings do not have holes, pressure exerted by wind may tear them off or make them fall. Holes let the air pass through and reduce the air pressure on banners and hoardings.

Q9: Describe an experiment to show pressure reduces when air moves with high speed.

Answer: Steps of the experiment are:
  1. Take a 2cm wide paper strip and hold it between the forefinger and thumb.
  2. Blow hard over its top. 
  3. Ensure fingers do not obstruct the flow of air while we are blowing.
  4. We see paper strip goes upwards instead of going down.
  5. Harder we blow, higher it rises up.
When we blow air over the paper, the air pressure above the paper reduces. The  air pressure below the paper remains the same. As the pressure below the strip is greater, it pushes the paper up.

Q10: Why are thatched roofs of huts blown off during high winds?

Answer: High speed winds reduce the air pressure above the roof. While the air pressure below roof is high which pushes the roof upwards. That's why roofs of the huts are blown off during high speed winds.

Q11: Name the scientist who discovered first time that when air moves with speed, its pressure drops.

Answer: Daniel Bernoulli.  His Bernoulli's principle laid the foundation of aeronautics.

Q12: How will you help your neighbours in case cyclone approaches your village/town?

Answer: On approaching of the cyclone, we should do the following:
  1. Help our neighbours and friends in shifting their important household goods, cattle and vehicles to safer places.
  2. Communicate with government agencies like police, fire brigade, medical centres and other emergency service points.
  3. We should store water for safe drinking.
  4. We should avoid driving roads nearby flood hit areas.

Q13: What planning is required in advance to deal with the situation created by a cyclone?

Answer: Self-help is the best help. Therefore it is better to plan in advance and be ready with defence against any approaching cyclone.
Planning required in advance to deal with cyclone-hit situation:
  1. Keep an emergency kit at home.
  2. Store enough food in water proof bags.
  3. Store safe drinking water as contaminated water can cause diseases.
  4. Keep phone numbers of emergency services like police, hospital, friends and relatives ready.
  5. Make necessary arrangements to shift the essential household goods, domestic animals and vehicles, etc. to safer places.

Q14: Which one of the following place is unlikely to be affected by a cyclone.(i) Chennai
(ii) Mangaluru (Mangalore)
(iii) Amritsar
(iv) Puri

Answer: (iii) Amritsar  is least likely to be affected by a cyclone because the city does not lie near to any coastal area.

Q15: 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: Correct statement is - (i) In winter the winds flow from the land to the ocean.

Q16: Define Cyclone.


Q17: What is a tornado?

Answer: A tornado is a violent, twisted funnel of high speed wind. It is formed when a funnel like column of cold air sinks down from a story cloud. Warm air rises up which whirls up causing high speed circulating winds.

(In progress...)