In this activity, learners investigate how changing the center of gravity of a balloon affects how it travels. Learners fill a balloon with a little bit of water and insert into an empty balloon. Then, learners inflate the outside balloon and throw it in the air. Learners will discover that the balloon moves oddly in a loopy fashion, because the inflated balloon has less mass than the water-filled balloon inside. Use this activity to demonstrate inertia, center of gravity, and mass.