illuminating science

Ever heard of ferrohydrodynamics? Nope, neither had I. From the name, it suggests something to do with metal or magnets (”ferro”), something to do with water (”hydro”) and some sort of resulting motion (”dynamics”) but words can’t really capture just how cool ferrohydrodynamics really is (not to mention the fact that it’s hard to say!)

In fact, ferrohydrodynamics describes is the motion of ferrofluids - liquids which respond to magnetic fields - when you apply strong and varying magnetic fields to them. In the ideal case, these fluids will remain as, er, fluids even when you apply very strong magnetic fields. Related are “magnetorheological fluids” which tend to solidy when you apply a strong enough magnetic field (I think due to clumping of the magnetic particles). A simple magnetorheological fluid can be made at home by mixing some magnetic particles into vegetable oil - apparently, using iron extracted from sand by a magnet makes a really good fluid, that will harden when a large magnetic is placed nearby.

To see these fluids in action, check out the utterly amazing movie from MIT of a high quality ferrofluid (one that won’t solidy) under the influence of rotating and opposing magnetic fields. They’ve created some amazing shapes that are really fascinating to watch as they evolve and change - it’s hard to believe it’s simply the result of a straight magnetic field! The actual description below the movie is beyond me, but it’s still neat to watch