Weather | Social Studies Textbook PDF

FOR ONLINE USE ONLY DO NOT DUPLICATE Chapter Three Weather Introduction When you were in Standard Four, you learnt about the concept of weather, weather elements and the instruments used to measure weather condi...

FOR ONLINE USE ONLY DO NOT DUPLICATE Chapter Three Weather Introduction When you were in Standard Four, you learnt about the concept of weather, weather elements and the instruments used to measure weather conditions. Also, you learnt about changes in weather conditions. In this chapter, you LY will learn the meaning of wind, which is one of the elements of weather. You will also learn about the causes, advantages and disadvantages of wind. Finally, you will learn how to measure wind. N O The meaning of wind SE Wind is air in motion. Wind blows from an area of high air pressure to an area of low air pressure. For instance, if you take a ball filled with air and then pierce it with a needle, you will find that the air inside the ball comes out. This happens because the air inside the ball is in high pressure, while the air U outside the ball is in low pressure. Causes of wind E Wind occurs because of differences in air pressure between one place and N another. An increase in temperature causes air to expand, become light and rise. This means air pressure becomes low. A decrease in temperature LI causes air to condense and sink. This makes an area have high pressure. The air from an area with high pressure tends to move to an area with low N pressure. When the difference in temperature between the two areas is O huge, the wind becomes strong. This is how wind occurs. Activity 1 R Take a balloon and blow it to fill it with air. When it is full, close the opening FO of the balloon. Pierce the balloon using a needle or a pin. You will see that air rushes out of the balloon. This shows how air flows from an area with high air pressure to an area with low air pressure. 25 SOCIAL STUDIES STD 5.indd 25 30/07/2021 11:49  FOR ONLINE USE ONLY Advantages of windDO NOT DUPLICATE Wind has the following advantages: (a) Pumping water from the ground: In windy regions or areas, wind is used to run windmills, which pump water from the ground. See an example of a windmill in Figure 1. LY N O SE U E N LI N Figure 1: A windmill pumping water from the ground (b) Generation of electricity: Wind can be used to run electricity-generating O machines. For example, Singida Region is one of the areas in Tanzania where wind is commonly used to generate electricity. So, we should R build windmills to generate electricity. This will help to reduce the use of other sources of energy such as fuel, wood, charcoal and gas. FO (c) Pollination of flowers: Wind acts as an agent in the pollination of flowers. Flower pollination is important because, without it, we cannot get fruits and seeds. 26 SOCIAL STUDIES STD 5.indd 26 30/07/2021 11:49  FOR ONLINE USE ONLY (d) DO NOT Drying clothes and grain: When DUPLICATE dry air blows, it absorbs moisture from clothes or grains and dries them. (e) Cooling the environment: In hot weather, people like to go to beaches for recreation. This is because the sea breeze blows cooler air from the oceans to the beach which is enjoyed by the people. Likewise, in hot weather, people use fans to cool their bodies. A fan is also used to cool car engines. (f) Formation of rain: When wind blows over a wet area, it absorbs moisture. If moist wind rises up and condenses, it forms clouds. Clouds LY become heavy and rain comes down. Disadvantages of wind N Despite having the advantages mentioned above, wind also has the following O disadvantages: (a) Destruction of buildings: A strong wind can blow away roofs and destroy SE houses sometimes. This may result in the loss of lives and can damage property (see Figure 2). U E N LI N O R FO Figure 2: Destruction of a building by a strong wind (b) Spreading of diseases: Strong winds blow dust that spreads bacteria and viruses of airborne diseases like tuberculosis and flu. 27 SOCIAL STUDIES STD 5.indd 27 30/07/2021 11:49  FOR ONLINE USE ONLY (c) DOvegetation: Destruction of natural NOT DUPLICATE Very strong winds such as hurricanes can uproot trees and hence destroy vegetation. (d) Causing floods: When strong winds such as hurricanes blow over a sea, they may cause floods on islands and the surrounding coastal areas. Exercise 1 Answer the following questions: 1. What is wind? LY 2. Describe causes of wind. N 3. Mention four benefits of wind. O 4. Explain two disadvantages of strong winds. 5. Mention two advantages of windmills. Measuring wind SE We can see two things when wind is blowing. These are the direction and U speed of wind. You can determine the direction of wind by looking at the direction in which trees or leaves sway. The speed of wind can be seen by looking at the shaking of trees and leaves or the blowing away of various E objects. The direction and speed of wind can be measured by using a special instrument. N The instrument used to measure LI the direction of wind is called a wind vane. At the top of this N instrument, there is an arrow that O shows the direction of wind. The arrow is hung on a pipe. Under the arrow there are wooden or R metal pieces that show the four cardinal points: North, East, FO South and West. When wind blows, the arrow turns towards the direction in which it is blowing Figure 3: A wind vane (see Figure 3). 28 SOCIAL STUDIES STD 5.indd 28 30/07/2021 11:49  FOR ONLINE USE ONLY Winds are given names toDO NOT identify DUPLICATE them. The name of a given wind depends on the direction from which it is blowing. For example, if the wind is blowing from South to North, it is known as a Southern wind. If the wind is blowing from North to South it is called a Northern wind. Similarly, if the wind is blowing from East to West it is known as an Eastern wind, and if the wind is blowing from West to East, it is called a Western wind. Wind speed is measured using an instrument called an anemometer. An anemometer is an instrument which has three or four horizontal cups on a vertical stand or shaft. At the end of each metal arm, a metal cup is LY fixed. When wind blows, the arms rotate and the speed of the wind is recorded in N kilometres or miles per hour. When the wind is strong, the O cups rotate fast. The number of circuits are recorded on a meter in the anemometer. The number shows the speed SE of the wind in kilometre per U hour. For example, in Figure 4, the speed of the wind is 28.3 kilometres per hour. Figure 4: An anemometer E N Ways to reduce the negative effects of wind We often hear from news that a strong wind has destroyed many houses LI in a certain region. The communities affected need to know how to protect themselves from the negative effects of severe winds. N The best way to protect ourselves from such effects is to plant trees in open O areas. Trees can reduce the speed of wind and ultimately minimize its effects on buildings. Moreover, houses built in areas with strong winds must have R strong walls and roofs. FO 29 SOCIAL STUDIES STD 5.indd 29 30/07/2021 11:49  FOR ONLINE USE ONLY Exercise 2 DO NOT DUPLICATE Answer the following questions: 1. What causes wind? 2. Outline three things that will show that a strong wind is blowing. 3. Why are open areas more affected by strong winds? 4. What should be done to reduce the effects of strong winds? LY 5. Why is one area more likely to be affected by strong winds than another area? N Match the words in Column A with the statements in Column B and then write the correct answers in the provided space. O No Column A Answer Column B 6. Anemometer ( ) (a) Measuring the direction of wind 7. Wind ( ) (b) SE One of the benefits of wind (c) Measuring wind pressure U 8. Unroof ( ) (d) Measuring the location of wind 9. Pollination ( ) (e) Measuring wind speed E 10. Wind vane ( ) (f) Air in motion N (g) A fast blowing wind LI (h) One of the disadvantages of wind N Vocabulary O Pollination the act of transferring pollen from the male anther to the female stigma for fertilization purposes R Windmill a tall thin structure with parts which use wind to produce FO electricity or pump water from the ground 30 SOCIAL STUDIES STD 5.indd 30 30/07/2021 11:49