This lesson focuses on molecular motion in gases. Learners compare the mass of a basketball when it is deflated and after it has been inflated. The inflated ball has the greater mass so learners can conclude that gas is matter because it has mass and takes up space. Then learners consider how heating and cooling affect molecular motion in gases. They dip the mouth of a bottle in detergent solution and observe a bubble growing and shrinking when the bottle is warmed and cooled. Learners will discover that the attractions between gas molecules are so minimal that attractions can’t be used to explain the behavior of gases like they can for liquids and solids.