Ferrofluid magnetic drops

To give the reader a flavor of the kinds of phenomena that can be predicted, we consider the simple case of a pool of ferrofluid, a portion of which is subjected to a weak magnetic field, at static equilibrium (see Fig. 8-14a). Thus, we drop the time derivative and the flow terms from Eq. (8-33), yielding... 

By placing a drop of their ferrofluid on a small piece of paper, stndents can observe another application of ferrofluids - as a magnetic ink. Ferrofluids stain the paper and the magnetite nanoparticles become embedded in the cellnlose paper material. The attraction of the magnetite towards a magnet can lift the paper. Magnetic inks such as this are part of the anti-counterfeiting measnres found in U. S. currency 24). 

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