Tue 29 Jul 2014
The other day I was playing with some soap bubbles and I started thinking: what makes them pop? And furthermore, sometimes they don’t pop, instead they will shrink down to nothing. So what causes each of these different behaviors? Can the failure mechanism be predicted? Can you predict when it will fail?
Basically the collapse of the bubble can be attributed to one of two mechanisms. 1.) The air inside of the bubble diffuses through the bubble film, causing the bubble to shrink and eventually collapse. 2.) The liquid in the bubble film evaporates, causing the film to get thinner and thinner until it finally ruptures, causing the bubble to pop.
First I’d like to analyze the bubble shrinking and collapsing, but I’ll split it into a series of posts. The first few will be brief explanations of specific pieces of physics that are needed in order to perform the analysis. The order I think I’ll do them in is the following:
1. Fick’s Law
2. Quasi-steady-state Approximation
2. Henry’s Law
3. Ideal Gas Law
4. Laplace Pressure
5. Geometry Simplification
Then I’ll show how to put all those pieces together to derive a single equation that shows how long the bubble will last until it collapses.
Or I might change my mind on the structure and the order part-way through. We’ll see.