Magnetohydrodynamics 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.
Special 10th anniversary edition of WHAT IF?—revised and annotated with brand-new illustrations and answers to important questions you never thought to ask—coming from November 2024. Preorder here!