CBSE Class 8 Annual Assessment

Chapter 6: Pressure, Winds, Storms, and Cyclones

Summary

This chapter connects the idea of pressure to powerful weather events. Pressure is defined as force per unit area, with the SI unit pascal (Pa), equal to one newton per square metre. Spreading the same force over a larger area lowers the pressure, which is why broad straps and broad handles feel more comfortable, while a sharp knife or pointed nail concentrates force into a high pressure. Liquids exert pressure not only at the bottom of a container but in all directions, and the pressure increases with the height of the liquid column, which is why overhead tanks are placed high. Air, too, exerts atmospheric pressure in all directions; a rubber sucker sticks because outside air pressure is higher than inside. Winds form because air moves from regions of high pressure to regions of low pressure, as shown with balloons and explained for land and sea breezes. High-speed winds are accompanied by reduced pressure, which can lift weak roofs. Storms, thunderstorms, and lightning are explained through rising warm moist air, condensation, charge separation in clouds, and the eventual flow of charge that produces lightning and thunder. Cyclones are large spinning low-pressure systems that form over warm oceans, with a calm eye at the centre, and the chapter stresses safety measures and the role of the India Meteorological Department.

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