5. Two Scales (Wrap Up)

Staecker, via Wikimedia Commons

To close this unit, students apply their new understandings as they annotate their graphs documenting mini-lake weight change across time. Their first annotations describe the sources of the weight and the observable changes across time (e.g., added salt; salt dissolved; removed cover; water evaporated) Their second round of annotations explain the mini-lake transformations at the particle level (e.g., particles of salt in the water became too small to see; particles of water moved from the surface into the air to become water vapor). Next students read the Why are these ships in a field? The Story of the Aral Sea to learn how the rivers that once fed the lake balanced the evaporation from the lakes surface, and how the sea has almost disappeared since that balance has been disrupted. Finally, students reflect on how their understandings of water transformations and matter have evolved as a result of their experiences with five specific elements of the unit: the mini-lake; the spray mister; the 2-bottle system; the Particle magnifier; and the syringe.

Investigations:

• Investigation 17: What's the story behind the graph?
• Investigation 18: How have our understandings changed?