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Activity: Stability of Water Layers

NGSS Science and Engineering Practices:

NGSS Crosscutting Concepts:

NGSS Disciplinary Core Ideas:

Materials

  • 2 rectangular, transparent plastic shoe boxes or small glass tanks
  • Hair dryer
  • Food coloring, four colors
  • Fresh water
  • Salt
  • Heat source
  • Ice bath
  • 2 beakers
  • Room temperature water
  • Spoon or stirring rod
  • Long, thin pipette
  • Paper towels

Procedure

Safety Note: Make sure that electrical items such as hair dryers do not come into contact with water, as there is a risk of electrocution. 

  1. Fill one box nearly to the top with room temperature fresh water.
     
  2. Fill the second box halfway with cold water. Cold water can be created by placing a beaker of water in an ice bath to cool it down.
     
  3. Heat a beaker of water using your heating source and add red food coloring to the water. Fill the top half of the second box with hot water. To prevent mixing of layers, gently and slowly pour hot water down a stirring rod, over the back of a spoon, or down the sides of the box.
     
  4. Predict how the surface water in each box will mix when disturbed by wind. Record your predications and reasoning.
     
  5. Add approximately three drops of blue food coloring near the bottom of both tanks using a long pipette, being careful not to disturb the water layers. Add three drops of green food coloring to the surface of both boxes.
     
  6. Use a hair dryer to produce wind, starting with the lowest setting. Angle the hair dryer so it is parallel to the surface to the water. Record your observations.
     
  7. Repeat the procedure using layers of different salinity.
    1. Fill the first box with room temperature fresh water.
    2. Fill the second box halfway with very salty room temperature water, colored yellow, and then carefully add a top layer with room temperature fresh water.
    3. Predict how the surface water in each box will mix when disturbed by wind. Record your predications and reasoning.
    4. Add approximately three drops of blue food coloring near the bottom of both tanks using a long pipette, being careful not to disturb the water layers. Add three drops of green food coloring to the surface of both boxes.
    5. Use a hair dryer to produce wind, starting with the lowest setting. Angle the hair dryer so it is parallel to the surface to the water. Record your observations.

 

Activity Questions: 
  1. What effect did the hair dryer (simulating wind) have on the water layers? How did your observations compare to your predictions?
     
  2. How was horizontal and vertical mixing similar or different in each of the boxes?
     
  3. What may have caused the differences in mixing in each of the boxes?
     
  4. How do you think mixing occurs in more than two layers? Explain your reasoning.
Exploring Our Fluid Earth, a product of the Curriculum Research & Development Group (CRDG), College of Education. University of Hawaii, 2011. This document may be freely reproduced and distributed for non-profit educational purposes.