Density Curriculum

Section 4—Lesson 14: Layering Liquids: How Does Density Affect Sinking or Floating?

Background Information

Relational Causality and Layering of Liquids

This lesson asks students to layer liquids to see the densities of the liquids as relational. The lesson then seeks to extend the learning to fluids more generally so that students realize that the understandings also apply to gases. These understandings are important for comprehending a variety of phenomena such as why oil floats on water, why our atmosphere is layered they way it is, and why certain chemicals sink and others float when released into water bodies.

One of the reasons why this lesson is important for many students is that it forces them to focus on the liquid. It is a powerful default assumption in thinking about sinking and floating to focus on the object only. If there is no object and only two liquids, it helps to force students' attention to the liquid as a part of the equation that influences the outcome.

Making Connections Between Relational Causality, Fluids, and Everyday Life

The lesson also encourages students to make connections between everyday life and the layering of liquids. How many of us have tried to clean out an oil jar by filling it with water and then tipping it over? The oil floats right back to the bottom of the jar as it is tipped up. This is a simple lesson in relational density.

There are many places where relational density can have a big impact. For instance, the layers of our atmosphere are arranged as they are because of the density of those fluids. Of course, there is lots of mixing of gases in our atmosphere given the behavior of gases. However, generally speaking, large shifts in the densities of gases in our atmosphere will result in shifts in the layering.