FYFD

For a little Friday fun, enjoy this timelapse of magnetic putty consuming magnets. Really this is a bit of slow-motion magnetohydrodynamics. The magnet's field exerts a force on the iron-containing putty, which, because it is a fluid, cannot resist deformation under a force. As a result, the putty will flow around the magnet, eventually coming to a stop once it reaches equilibrium, with its iron equally distributed around the magnet. Assuming the putty is homogeneously ferrous (i.e. the iron is mixed equally in the putty), that means the putty will stop moving when the magnet is at its center of mass.  (Video credit: J. Shanks; submitted by Neil K.)

The solar wind, a rarefied stream of hot plasma ejected from the sun, constantly bombards Earth's magnetic field. This results in the formation of the magnetosphere, which deflects most of these charged particles away from the earth. Some of them, however, are drawn toward the magnetic poles; when these charged particles strike the upper atmosphere, they cause the gases there to release photons, resulting in the lights we know as auroras. This animation shows the International Space Station flying through the aurora australis--the southern lights. The fluid-like motion of the aurora is no accident; though diffuse, the solar wind is still a fluid governed by magnetohydrodynamics.

Here's a ferrofluid video with a little more explanation about how ferrofluids work. Surfactants prevent the tiny magnetic particles suspended in the fluid from separating out when exposed to a magnetic field.

If a fluid is electrically conductive, then magnetohydrodamics (often abbreviated as MHD) describe its behavior. Electric and magnetic fields can be used to stir such a fluid, as in the video above. By inducing a potential difference across the electrodes lining the walls and the disk-shaped electrodes far from the walls, complicated flow patterns can be produced. #

Magnetism and fluid dynamics collide with ferrofluids! Ferrofluids are a suspension of ferrous material in oil or water, but their behavior around magnets can elevate them into a work of art (or a car commercial). Why leave it to professionals, though, when you can make your own ferrofluid?