Retirement & leaky bathtubs; 2 metaphors - 1model
If WATER / MONEY comes into a BATHTUB / BANK at a constant rate
and leaks out a rate proportional to the HEIGHT / AMOUNT of the
WATER / MONEY in the BATHTUB / BANK, then an equilibrium HEIGHT / AMOUNT
of WATER / MONEY in the BATHTUB / BANK can be reached.
You can use this applet to explore how the equilibrium depends
on the rate of flow into and the rate of flow out of the BATHTUB / BANK.
Clearly, the BATHTUB / BANK is a metaphor for many equilibrium situations
that arise because of competing rates. Can you think of others?
You can watch an animation by clicking on the "play" icon in the lower
left hand corner of either window.