NCERT Class 7 Science Chapter 8 - Winds, Storms and Cyclones Notes

Chapter 8 - Winds, Storms and Cyclones Notes

1. The moving air is called wind.

2. Air exerts pressure on all object. This is called air pressure.

3. Increased wind speed is accompanied by a reduced air pressure.

4. Air moves from a higher pressure region to a lower one. The greater the difference in pressure, the faster the air moves.

5. On heating the air expands and occupies more space. Hence, it becomes lighter. The warm air is, therefore, lighter than cold air. That is the reason that the smoke goes up.

6. At a place, where warm air rises, the air pressure is reduced and the cooler air moves to that place.

7. Wind currents are generated due to uneven heating on the earth. High speed winds are accompanied by reduced pressure.

8. Regions nearer to the equator get maximum heat from the sun. The air in these regions gets warm. The warm air rises, and the cooler air from the region in the 0-30 degrees latitude belt on either side of the equator moves in.

9. At the poles, the air is colder than that at latitudes about 60 degrees. The warm air at these latitudes rises up and the cold wind from the polar regions rushes in, to take its place. In this way, wind circulation is set up from the poles to the warmer latitudes.

10. Due to uneven heating of land and water, in summer, the land near the equator warms up faster and most of the time the temperature of the land is higher than that of water in this oceans.

11. In winter, the direction of the wind is from the land to the ocean.

12. The wind from the ocean carry water and bring rain. It is a part of the water cycle.

13. The monsoon winds carry water and it rains.

14. The winds blow from the oceans towards the land in summer. These are called monsoon winds.

15. There are certain situations, in nature itself, which can sometimes create disasters like thunderstorms and cyclones. They pose threat to humans, animals and plant life.

16. The strong upward rising winds produced by the rising temperature carry water droplets upward where they freeze and fall down again. The swift movement of the falling water droplets along with the rising air create lightning and sound. It is this event that is called thunderstorm.

17. The chain of events of thunderstorm ends with the formation of a very low-pressure system with very high-speed winds revolving around it. It is this weather condition that we call a cyclone.

18. A cyclone is known by different names in different parts of the world. It is called a ‘hurricane’ in the American continent. In Philippines and Japan it is called a ‘typhoon’.

19. Tornado is a dark funnel-shaped cloud that reaches from the sky to the ground.

20. The word monsoon is derived from the Arabic word ‘mausam’, which means ‘season’.

21. The centre of a cyclone is a calm area. It is called the eye of the storm. A large cyclone is a violently rotating mass of air in the atmosphere, 10 to 15 km high. The diameter of the eye varies from 10 to 30 km. It is a region free of clouds and has light winds. Around this calm and clear eye, there is a cloud region of about 150 km in size. In this region there are high-speed winds (150-250 km/h) and thick clouds with heavy rain. Away from this region the wind speed gradually decreases.

22. If a storm is accompanied by lightning, we must take the following precautions:
• Do not take shelter under an isolated tree. If you are in a forest take shelter under a small tree. Do not lie on the ground.
• Do not take shelter under an umbrella with a metallic end.
• Do not sit near a window. Open garages, storage sheds, metal sheds are not safe places to take shelter.
• A car or a bus is a safe place to take shelter.
• If you are in water, get out and go inside a building.

23. The diameter of a tornado can be as small as a metre and as large as a km, or even wider. The funnel of a tornado sucks dust, debris and everything near it at the base (due to low pressure) and throws them out near the top.

24. All storms are low-pressure systems. Wind speed plays an important role in the formation of storms. It is, therefore, important to measure the wind speed. The instrument that measures the wind speed is called an anemometer.

25. Some other precautions, if you are staying in a cyclone hit area -
• Do not drink water that could be contaminated. Always store drinking water for emergencies.
• Do not touch wet switches and fallen power lines.
• Do not go out just for the sake of fun.
• Do not pressurise the rescue force by making undue demands.
• Cooperate and help your neighbours and friends.

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