What is a common factor that affects soap bubble longevity?

• A. Gravity-induced drainage and evaporation
• B. Viscosity of soap solution
• C. Ambient lighting conditions
• D. Air humidity levels

Answer: (A)

Bubble longevity comes down to how quickly the soap film thins until it can no longer support itself. Gravity pulls liquid in the film downward, so the film drains over time. As the liquid drains, the film becomes thinner, especially near the top, and this thinning makes it more prone to rupture. Water also slowly evaporates from the film, further reducing thickness and weakening the structure. Together, drainage and evaporation determine how long a bubble can last.

Other factors can influence the rate somewhat. A more viscous soap solution can slow drainage and help the bubble persist longer, but that’s not the main driver. Ambient lighting doesn’t affect the physics of the film. Humidity can change how fast water evaporates—higher humidity slows evaporation a bit—but the fundamental reason a bubble fades is the combination of gravity-driven drainage and evaporation thinning the film.