This activity explores LaPlace’s law where membranes exert pressure on their contents that decrease as the membranes are stretched to larger sizes and their thickness decreases. The internal pressure of a spherical balloon is inversely proportional to its radius—as a balloon is inflated and its size increases, the internal pressure of the trapped gases decreases. The combined mass (but not volume) of the gases is conserved in this closed, two-balloon system. This provides an opportunity to investigate the nature of science via a cycle of predict-observe-explain.