Percolation

Percolation is like a game of dominos. Imagine dominoes lined up on a table in a chain. When you push over the first domino, it falls over and hits the second one, causing the second one to fall over and the third one, and the third one to fall over and so on. This is kind of like percolation.

In percolation, there is usually a solid material (like sand or rocks), a material that lets liquids pass through it (like sand), and a liquid. When the liquid touches the material, it spreads through it like the dominoes are falling on each other--the liquid percolates. Eventually, the liquid spreads through enough of the material that a path is formed and the liquid moves along this path.