Chapter 8: A Journey through States of WaterClass 6 Science — summary, notes, extra questions & NCERT solutions

Summary

This chapter follows water through its three states and the processes that change one into another. It first establishes that ice and water are two forms, or states, of the same substance, differing only in behaviour — water flows and splashes while ice does not. Investigating where water from puddles and wet utensils disappears, the chapter shows water does not seep through a steel plate but instead turns into an invisible gas called water vapour; this conversion of water into vapour is called evaporation, which happens continuously even at room temperature (drying clothes, mopped floors, and sweat are examples). A second mystery — water droplets forming on the outside of a cold glass tumbler — is explained by condensation, the conversion of water vapour in the air into liquid water when it meets a cold surface, confirmed by an increase in mass on a weighing balance while the water level inside does not fall. The chapter compares the three states: ice (solid) keeps its shape and does not flow or spread; water (liquid) flows, spreads, and takes the shape of its container while keeping a fixed volume; water vapour (gas) spreads to fill all available space and has no fixed shape. States change with heating and cooling: melting is solid to liquid, freezing is liquid to solid, evaporation is liquid to gas, and condensation is gas to liquid. Evaporation is faster with a larger exposed area, in sunlight or warmth, with more air movement, and slower when humidity is high; evaporation also causes a cooling effect, as seen in earthen pots, surahis, and the pot-in-pot cooler. Finally, condensation high in the atmosphere forms clouds around dust particles, which grow into raindrops; this whole circulation of water between the Earth and the atmosphere is the water cycle, and the chapter urges us to use water wisely.

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