This lesson demonstrates that air takes up space, and puts pressure, or pushes, on everything around it. In this activity, students will be conducting investigations that will help them develop and refine their ideas about air. To start the lesson, students will be asked to write an explanation of what air is. At various points in the lesson they will be asked to revisit their explanations and refine them based on the phenomena they have experienced in the lesson. This lesson addresses some of the physical properties of air on the substance level in order to help students build toward future understanding of how air particles behave on a molecular level.