Ferrofluid
Check out these amazing video clips of ferrofluid, a solution containing nanoscale particles that respond to a magnetic field.
VIDEO [1] (via wohba!> kottke.org) VIDEO [2] (via wohba!> kottke.org) VIDEO [3] (via wohba!> kottke.org)
LINK/IMAGES [find/scroll to ferrofluid] (Dan’s Data) IMAGES (credit: Minako Takeno) IMAGE (credit: Felice Frankel, National Geographic) LINK [Wikipedia article]
You can buy this from a number of places online, but Dan from Dan’s Data (above) recommends Educational Innovations, “who sell all sorts of things that science teachers need. Or don’t need, but want anyway, because if you’re going to have to deal with annoying teenagers all day for not enough money, you might as well play with some cool toys by way of compensation.” Makes me want to be a teacher all over again.
BUY [100ml = $30]
Update: Sachiko Kodama does interesting things with ferrofluid, and has lots of video on her website: