Winds, Storms and Cyclones

Air exerts pressure in all directions, which is why a balloon or a tyre swells when air is pumped in. Blowing over a strip of paper shows that high-speed winds are accompanied by reduced air pressure. Air expands on heating, becomes lighter and rises, and cooler air moves in to take its place. Wind is moving air, and it always blows from a region of high pressure to a region of low pressure. Uneven heating of the Earth, between the equator and the poles and between land and water, produces winds, including the monsoon winds that bring rain to India. Thunderstorms develop in hot, humid tropical areas when warm, moist air rises rapidly, causing lightning and heavy rain. A cyclone is a huge storm with very high-speed winds spiralling around a calm centre called the eye. Cyclones are called hurricanes in the Americas and typhoons in the Philippines and Japan, while a tornado is a dark funnel-shaped cloud. Weather warnings, cyclone shelters and timely evacuation reduce damage, and wind speed is measured by an anemometer.

Detailed Worksheet: Winds, Storms and Cyclones Section A - Definitions (10 marks) 1. What is wind? In which direction does it blow? (2 marks) 2. What is air pressure? Give one example showing that air exerts pressure. (2 marks) 3. What is a cyclone? What is the eye of a cyclone? (2 marks) 4. What is a tornado? Where are tornadoes common? (2 marks) 5. Name the instrument used to measure wind speed and describe it in one sentence. (2 marks) Section B - Calculations and Applications (15 marks) 6. Explain how uneven heating between (i) the equator and the poles (ii) land and water causes winds. Give one example. (3 marks) 7. Why does a sheet of paper rise when you blow over it? Why do roofs of houses sometimes get blown off in storms? (3 marks) 8. List three safety measures to be taken during a thunderstorm when outdoors, and two when indoors. (3 marks) 9. A cyclone moves towards the coast at 20 km/h and is 300 km away. (i) How many hours will it take to reach the coast? (ii) If it is spotted at 6 pm, at what time will it reach the coast? (iii) Why are early warnings important? (3 marks) 10. Name the cyclone of each type based on region: (i) Americas (ii) Philippines and Japan (iii) India. Name two states of India often hit by cyclones. (3 marks) Section C - Diagrams (10 marks) 11. Draw a labelled diagram of the structure of a cyclone showing the eye, the spiralling winds and the clouds around the eye. (4 marks) 12. Draw a diagram showing how warm air rises and cool air takes its place, using a candle and a paper spiral, or using arrows over land and sea. (3 marks) 13. Draw a labelled diagram of the activity with a bottle, a paper ball and air blown across its mouth, or two balloons hung near each other, to show that high-speed air has low pressure. (3 marks) Section D - Analysis and Higher-order Thinking (15 marks) 14. The monsoon winds bring rain to India every year. (i) Why do winds blow from the ocean to the land in summer? (ii) Why do they carry water vapour? (iii) What happens to farmers if the monsoon is weak? (iv) In which direction do winter winds blow? (v) Why do they carry little rain? (5 marks) 15. A cyclone is expected in a coastal village. (i) List three things the government should do. (ii) List three things the villagers should do. (iii) Why should they not go out during the calm of the eye passing over? (iv) Why must people avoid driving on flooded roads? (5 marks) 16. Lightning often strikes tall trees and buildings. (i) Why should we not stand under a tree during a thunderstorm? (ii) Why is a car or bus a relatively safe place? (iii) What is a lightning conductor? (iv) Why should we not use phones connected by wires during a storm? (5 marks) Instructions: Time allowed 2 hours. Attempt all sections. Show arrows for the direction of wind in all diagrams.