Colloids and Emulsions. These materials are very common and are amenable to some nice demonstrations, yet are not part of the usual curriculum. Topics include surface tension (and why droplets are spherical; why shaving cream acts like a solid even though it's made of liquid and gas); Brownian motion and the microscopic origin of heat; the behavior of many particles (phase transitions, how colloidal particles can spontaneously order themselves – an accurate demonstration of how water molecules form ice crystals); what is inside everyday materials.