Here are some videos of an art installation by Bruce Shapiro  [LINK] called "Sisyphus III".

Sisyphus was a king in Greek mythology, punished in the underworld by being set to roll a huge boulder up a hill throughout eternity.
[LINK]

This thing works the same way. It’s a table of sand. On the surface is a steel ball. Underneath the table is a plotting mechanism that moves a magnet, causing the ball to move with it. The result is a line in the sand. Control the whole thing with a computer and you end up with beautiful, transient patterns drawn on the table top.

Videos are here: [LINK][LINK][LINK][LINK]