106. Why don't soap bubbles float forever (I believe they fall when not influenced by wind currents) if you have the "same" air both inside and outside the bubble?
The average density of an air-filled soap bubble is just slightly higher than that of the surrounding air. That's because the soap film itself is denser than air and because the air inside the bubble is very slightly compressed, thus having a slightly higher density than the surrounding air. Because the bubble's average density is slightly higher than that of the surrounding air, the bubble will slowly sink in still air and will eventually reach the ground.