Water cycle


    To know what the water cycle consists of and relate the change of states of water in different phases

Water Cycle

    The sun’s heat causes evaporation of water into vapour. When the water vapour cools down, it condenses and forms clouds. From there it may fall on the land or sea in the form of rain, snow or sleet. The process by which water continually changes its form and circulates between oceans, atmosphere and land is known as the water cycle. See figure 1.


                                                                   Figure 1: Water Cycle

Processes involved in water cycle:

     The four major processes that are involved in the water cycle are evaporation, condensation, precipitation, and run-off.

1. Evaporation

     Evaporation is the process of a substance in a liquid state changing to a gaseous state due to an increase in temperature and/or pressure.

2. Condensation

     Condensation is the process through which the physical state of matter changes from the gaseous phase in to the liquid phase.

3. Precipitation

     The process by which once the water vapour condenses to form water droplets in clouds and once they become heavy enough, fall to the ground in various forms such as rainfall, snowfall, hail, etc.

4. Run-off

      After rainfall the excess water which remains unasbsorbed by earth, remains on land’s surface and flows as surface water in to the creeks,streams or ponds. This water flow is called as Run-off.