Guiding Question: Why are some liquids denser than others?

1. Explaining the model. This picture shows a large liquid filled tank in the center and a selection of liquid filled balloons to the right hand side and alternative liquid filled tanks to the left. In this simulation, different balloons can be placed into the tank of liquid in the center to see if and how the balloons sink or float. The liquid in the tank can also be changed. The simulation also allows the user to select a molecular view, to observe the relative number and proximity of the molecules in each liquid.
2. Demonstrate an investigation. Explain that in this selected tank there is room temperature water and into it you will drop a balloon filled with salt water. Ask the students to predict what will happen to the balloon and explain why they think that.
3. Run the simulation.
4. Molecular View. Reset the simulation to show the molecular level in the balloon. Drop the salt water balloon in the room temperature water tank again. Have students describe what they notice to a partner. [There is more “stuff” (matter) in the salt water. The molecules are closer together.]
5. Design investigations and predict what will happen. Have students select a liquid for the tank then predict how the balloons containing different liquids will behave when they are added to it. Ask students to explain why they think this will happen.How would you explain what density is to someone who had never heard about it before?

The following simulation activity derives from Session 1.8 of the OSS 6–8 curriculum. Students explore nine different model oceans in which currents are created, to help them build an explanation for what causes ocean currents. If students explored the Density of Liquids mini activity above, they will bring the understanding that denser substances sink below substances that are less dense, and that cold water is denser than warmer water, and salty water is denser than less salty water.