A printed copy of this module can be purchased at the Project Zero e-bookstore.
	Acknowledgments
	Introduction Overview Challenges in Understanding Air Density What Students Need to Know About Matter, Mass, and Volume Instructional Approach Endnotes for Introduction
	Section 1: Visualizing Density: Density is Non-obvious Lesson 1: How Can Objects of the Same Volume Differ in Mass? Lesson 2: What Are Some Models That Help Us Think About Density? Resources for Section 1 Endnotes for Section 1
	Section 2: Defining Density as a Relationship Lesson 3: What Patterns Can Be Found Between Mass, Volume, and Density? Lesson 4: How Can We Calculate Density From The Relationship Between Mass and Volume? Lesson 5: Why Is Density Considered a Property of a Particular Kind of Matter? Lesson 6: Do Liquids Have Density? Lesson 7: Do Gases Have Density? Resources for Section 2
	Section 3: The Causes of Differences in Density Lesson 8: How Does Atomic Mass Contribute to Density? Lesson 9: How Do Atomic and Molecular Bonds Contribute to Density? Lesson 10: How Does Mixed Density Contribute to Overall Density? Lesson 11: What Does It Mean for Density to Have Multiple Contributing Causes? Lesson 12: Can the Density of Solids, Liquids, and Gases Change? Resources for Section 3
	Section 4: The Role of Density in Sinking or Floating: Relational Causality Lesson 13: Dropping an Object into a Liquid: How Does Density Affect Sinking or Floating? Lesson 14: Layering Liquids: How Does Density Affect Sinking or Floating? Lesson 15: What Happens in Sinking or Floating When the Relationship Between Densities Changes? Resources for Section 4 Endnotes for Section 4