Theory: Temperature-sensitive liquid crystals can be used to show how heat conducts along a metal bar, as their color depends on their temperature.
Description: These liquid crystals are red at 25 °C, violet at 30°C, and the other colors of the spectrum in between. Boiling water should be placed in one of the styrofoam containers, and room-temperature water in the other. When the bar is placed with one end in the hot container and one end in the cold, heat will be conducted along the bar. A thin red band slowly works it's way along the bar as the temperature goes up, and the other colors follow behind.
The liquid crystal must be brightly illuminated, because you need a lot of reflected light to see the colors. Placing a light bulb in front of it is a good idea.
Setup time: 10 minutes
References: (available in the demo room)