Put a lid on it! In small groups students will explore density in a water system.


Students will understand the physical processes associated with dead zones, as well as the concepts of density and stratification. Students will also be challenged to think critically about a simple demonstration, and hypothesize about various outcomes of the demonstration.

density layering



  1. Add 1 gram of salt to 5 ml of cold water. Mix thoroughly in a cup to dissolve salt. Add 1 drop of food coloring.
  2. Pour into a 10 ml graduated cylinder.
  3. Add 5 ml warm water to another cup. Add 1 drop of a different colored food coloring.
  4. Using a medicine dropper or pipette add fresh warm water to the graduated cylinder containing the cold salty water (the two waters should not mix).
  5. Check that the graduated cylinder with separated water masses looks similar to picture.
  6. Students think/pair/share to brainstorm different ways they can mix the water (earthquake, tornado, hurricane, winter change top water cold).
  7. Ask the students to try to mix the water with one of the ideas from their think/share/pair. 


 Discussion Questions

*Optional: review concept using video of density tank (scroll down to view video).

National Science Education Standards

K-12: Unifying Concepts and Processes

9-12 A: Science as Inquiry
9-12 B: Physical Science