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Dynamic sculpture by ferrofluid artist Sachiko Kodama.


The study of fluid flow probably started long before Archimedes' invention of the water screw about 2300 years ago. Though it was a long time after that before mathematicians put serious thought into describing fluids with equations. One of the early successes came in the 1700's, when Leonard Euler produced a breakthrough mathematical model of a fluid with no viscosity. His equations were later modified to include the effects of viscosity and entropy. Mathematicians, engineers and physicists have been struggling to understand the solutions to these equations ever since. One open question is worth $1,000,000 to anyone who answers it.

By comparison, the study of electromagnetism is fairly young. I've heard tales that certain ancient peoples may have understood how to construct simple chemical batteries. But as recently as the 1750's, Ben Franklin was electrocuting kites with lightening bolts, with no idea of what was happening. It wasn't until the 1870's that James Clerk Maxwell constructed the first detailed mathematical model of electromagnetism. Relativistic effects weren't included until after Einstein's work in the early 1900's.

So what happens when a fluid is influenced by electromagnetic fields? What strange world is born from this fusion of complex systems? Scientists, mathematicians, and hobbyists have discovered only a small subset of the answers, but what they do know is fascinating.


The partial differential equations of magnetohydrodynamics: the marriage of Euler and Maxwell.

Ferrofluids
By mixing certain ferromagnetic metal powders with soaps and oils, you can make a high viscosity fluid with a lot of surface tension that responds in beautiful ways to the influence of magnets. The video at the top of this article shows one of these fluids producing beautiful spiked dynamic patterns in response to a magnetic field controlled by artist Sachiko Kodama. The high viscosity and surface tension keeps the metal powder particles from being ripped out of suspension by the magnets. The spikes arise because the metal particles are being forced along magnetic field lines. The fluid part of a ferrofluid does not respond well to magnets. The behavior of a ferrofluid is due solely to the embedded metal particles.

Paramagnetic Liquids

Paramagnetic liquid oxygen being attracted to a strong magnet.

Certain liquids, liquid oxygen for example, have inherent magnetic properties. Unlike ferrofluids, which are magnetic because of particles suspended in them, paramagnetic fluids respond to magnets because every molecule in the fluid has unpaired electrons.

Magnetofluids

The violent magnetohydrodynamics of the sun's surface.

When electrons move, a magnetic field is created. So, if a fluid contains streaming free electrons and is also able to respond to magnetic fields, it becomes a self-driven magnetic dynamo. Magnetic fields cause changes in fluid flow and fluid flow causes changes in the magnetic field. This type of fluid is found in stars and fusion reactors. Much of our own sun's strange behavior, including sunspots and solar flares, is caused by this dynamo. Online science news magazine Wired.com recently had an article describing the bizarre activity on our sun's surface. Read the full article to see some beautiful photos and learn why sunspots usually occur in 11-year cycles.

Labels: Euler, ferrofluid, liquid, magnet, Maxwell, sunspots