A simple educational tool in fluid dynamics. Graphite flakes make a beautiful rheoscopic fluid. The flakes also react to a magnetic field, aligning with the field direction.
Combine these two phenomena and you can produce interesting flow models and even streamlines around objects like cylinders and airfoils. Cylinders produce the well known Von Karman vortex patterns.

Chapters:
0:40 Magnetic effect on floating graphite
1:40 Magnetic effect on dry flakes
2:24 Magnetic effect on rheoscopic fluid
3:08 Halbach arrays
4:00 Flow around cylinder and ellipse
5:30 Making streamlines
6:07 Flow around a NACA 0020 airfoil