Density Curriculum

Section 2—Lesson 6: Do Liquids Have Density?

Background Information

A Limited Focus on "Material Kind" and Objects

Students often think of density as having to do with "stuff," or what a material is made of, which in their minds, includes only solids. A strong focus on "material kind" as the underlying cause of density can inadvertently reinforce this focus. In addition, fluids, especially gases, can be non-obvious to most students. If you can't see something it is hard to acknowledge its existence or reason about it.

Liquids and Gases Have Density

The next two lessons focus on liquids and gases and attempt to convince students that because they take up space and have mass, they must have density. Realizing that we can find the density of solids, liquids, and gases is important for transferring understandings about density to weather systems, convection currents and other real-world phenomena.

Gases and liquids are both fluids. The main difference between them is the distance between their molecules. In gases, the molecules are far apart, so they move about more freely and aren't affected as much by forces between molecules. In liquids, the molecules are close together, and so the forces of the surrounding molecules affect each other. Both liquids and gases take the shape of the container that they are in.