Revision Notes: Class 8 Science Chapter 6 Pressure Winds Storms and Cyclones

Class 8 Science Chapter 6: Pressure, Winds, Storms and Cyclones — Quick Revision Notes

• Pressure: Force ÷ Area; SI unit pascal (Pa) = N/m². The same force spread over a larger area produces lower pressure, and vice versa.
• Liquid pressure: liquids exert pressure in all directions — on the base and the walls of a container, not just downward.
• Liquid pressure and height: increases with the height/depth of the liquid column, independent of the container’s shape or width — why overhead tanks are built tall and placed high.
• Wind: the movement of air from a region of higher pressure to a region of lower pressure.
• Sea breeze (daytime): land heats faster than the sea, air over land rises creating low pressure, and cooler high-pressure sea air flows in to replace it.
• Land breeze (night): the reverse process — land cools faster than the sea after sunset.
• Thunderstorm formation: warm moist air rises and cools → water vapour condenses into droplets/ice → charge separates (positive ice near the cloud top, negative water droplets lower down) → sudden discharge produces lightning, and the rapid heating/expansion of air produces thunder.
• Cyclone: intensifies over warm ocean water as rising moist air creates a very low-pressure centre; surrounding air rushes in and, due to Earth’s rotation, begins to spin.
• Eye of a cyclone: the calm, low-pressure centre, surrounded by a ring of the storm’s highest wind speeds.
• Safety: during thunderstorms, avoid isolated tall trees and open fields, and a car’s metal body offers protection; during cyclones, stay indoors and away from windows.
• Why banners/hoardings have holes: holes let wind pass through, reducing the pressure difference (and hence the net force) between the two faces that would otherwise tear the structure loose.

Written by Satish

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