Motion in Interstellar Clouds
Purpose
Pepper sprinkled on freshly poured water exhibits random motion that quickly organizes into coherent rotation, modeling how interstellar gas clouds develop net angular momentum from initially disordered motion. Illustrates the statistical inevitability that random velocities won't perfectly cancel, and how conservation of angular momentum amplifies this during gravitational collapse.
Figure 1:
Equipment: shallow glass dish (for overhead projector), water, and ground black pepper.