In this activity and/or demonstration, learners illustrate visually and physically that air has weight. Learners balance two equally-inflated balloons hanging from string on a yard stick. Learners observe what happens when they remove the air from one balloon. Learners will discover that the yard stick will become unbalanced once the weight of air is removed from one side. Use this demonstration to introduce learners to air pressure. This lesson guide includes information about how air pressure relates to baseball as well as severe thunderstorm safety.