My physics high school teacher’s favorite example for exponential decay was not the textbook one, but rather the decay of foam bubbles in a glass of beer.
These were good times. Chernobyl was still many years away, and one could happily replace cold war fears of a global nuclear disaster by that of an indecent amount of foam in a beer.
Not so anymore. Dangerous alcohol has been replaced by even more dangerous drugs, and the surprisingly capable and reasonable politicians by maniacs. Why? How?
This year I am teaching probability, and have replaced some of the rather morbid text book exercises by ones containing bubble baths, to protect my students from being traumatized by reality. What is the half-life of moral standards?
The large amount of foam on our pristine creeks are called surfactants, and can have natural or human causes.
Making that distinction is quite telling.