Lessons · Teaching · the water cycle
The same water, going round, driven by the sun
Water evaporates from oceans and land, condenses into cloud droplets as it rises and cools, falls as precipitation, and returns by runoff and groundwater to the sea. The sun supplies the energy and gravity brings it back down. No water is created or destroyed.
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In beta. This lesson was written for Hone and has not yet been checked by a state certification officer. Practice material, not professional advice. What that means.
What it is for
The sentence worth leaving a class with is that the water in their glass has been through the cycle many times. It makes conservation concrete, and it makes the cycle a mechanism rather than a poster with four arrows.
How to think about it
Follow one drop all the way round and name the energy at each step. Evaporation needs heat in; condensation gives heat out and requires cooling, which is why it happens as air rises. Transpiration from plants counts as part of the evaporation stage.
Worked example
Evaporation: liquid water becomes vapour, using energy from the sunHeat goes in. This is why a puddle dries faster in sunshine.
Condensation: rising air cools and vapour becomes droplets, forming cloudCooling is the trigger, and height is what supplies the cooling.
Precipitation: droplets join until they are heavy enough to fallRain, snow, sleet or hail, depending on the temperature on the way down.
Collection: water runs off into rivers or soaks down into groundwater, and reaches the seaThe return leg, and the slowest one.
Your turn
Name the stage in which water vapour becomes liquid droplets.
Vapour becomes droplets by
Solve one, graded on the server
The trap
Saying clouds are made of water vapour. Vapour is an invisible gas; a cloud is visible because it is liquid droplets or ice. If you can see it, it has already condensed.