We have a stored quantity of something, like water in a temporary pond,
which is percolating into the ground. As the pressure driving it decreases,
the water draws out - quickly at first and then slowly.
Water diffusing through sand
Decay of radioactivity of elements like uranium
Q = stored quantity
K = Decreasing factor
DQ = -K*Q
The graph shows changes of Q over a time period.Source code: Drain.java
"What if" Experiments:
Think about a pile of leaves which is being decomposed by microbes:
If you started with a larger pile of leaves in the forest, with the same
rate of composition, would the pile go sooner, at the same time or later?
What happens if the decomposing rate of the microbes is doubled?