Magnetohydrodynamics

Magnetohydrodynamics

(alt-text)

Magnetohydrodyanmics combines the intuitive nature of Maxwell's equations with the easy solvability of the Navier-Stokes equations. It's so straightforward physicists add "relativistic" or "quantum" just to keep it from getting boring.

There are four new shirts in the xkcd store,
along with posters and lots of other stuff!