Learners cover a bottle with a balloon. When they immerse the bottle in warm water, the balloon inflates. When they immerse the bottle in a bowl of ice, the balloon deflates. Learners understand that warm air is less dense than cool air (it has the same mass, but more volume). This is one of three demonstrations investigating convection currents and their effects on weather and air pollution. Resource contains vocabulary definitions and suggestions for assessment, extensions, and scaling for different levels of learners.