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Have you ever walked along a beach and wondered why some parts were sandy and other parts were rocky?  When the waves hit the beach, the sand and rocks carried in the water are deposited.  The denser rock particles are dropped first along the shore, while the less dense sand particles are carried farther up the beach.

Lets look at an example of materials sorting based on density and particle size.



  • Graduated cylinder or other container (e.g. empty soda bottle)
  • Soil
  • Water


  1. Take some soil and mix it with water.
  1. Mix the soil and water together and shake vigorously.
  1. Let the mixture sit for at least one day.
Look closely to see the various layers which result from nature's sorting!


  1. How did the solution of soil and water change from when you first shook them up until after you let them sit for at least a day?
  2. Sand grain A has a density of 2.0 g/cm3, and sand grain B has a density of 1.5 cm3, but they both have the same size. Which of these would settle out first when mixed in water?
  3. How is this example similar to what happens where a river enters a lake?

Review science safety rules here.

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Teachers should view the Teacher Site Map to relate Sci-ber text and the USOE 7th grade science core.

Updated October 24, 2008 by: Glen Westbroek

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