Chapter 8: A Journey through States of Water
Puddles vanish, cold glasses get wet outside, clouds pour rain. In this chapter we follow water as it evaporates, condenses, melts and freezes, find out what makes evaporation faster, why evaporation cools, and how the water cycle brings us rain.
In this chapter you will
- explain evaporation and condensation
- describe the three states of water and how they change
- name factors that speed up evaporation
- explain the cooling effect and the water cycle
Topics
- Water's Disappearing Act NCERT 8.1–8.2
Evaporation: liquid water → water vapour, from the surface, at any temperature.
- States of Water NCERT 8.3
Water exists as solid (ice), liquid (water) and gas (water vapour).
- Changing the State of Water NCERT 8.4
Melting (0 °C), freezing, boiling (100 °C), evaporation and condensation are changes of state.
- Faster or Slower Evaporation NCERT 8.5
Evaporation is faster with more surface area, heat and wind, and lower humidity.
- Cooling Effect NCERT 8.6
Evaporation causes cooling: it takes heat from the surface.
- How Clouds give us Rain NCERT 8.7
Evaporation, condensation and rain keep water moving in the water cycle.
Key words
- Evaporation
- liquid water changing into water vapour
- Condensation
- water vapour changing back into liquid water
- Melting / freezing
- solid → liquid / liquid → solid
- Boiling point
- 100 °C for water
- Humidity
- the amount of water vapour in the air
- Water cycle
- the endless journey of water between earth and sky
Summary
- Water exists as solid, liquid and gas, and changes state on heating or cooling.
- Evaporation happens from the surface at any temperature; boiling happens at 100 °C.
- Surface area, heat, wind and humidity affect the rate of evaporation; evaporation causes cooling.
- Evaporation, condensation and rain make up the water cycle.