PURPOSE: To illustrate buoyancy and the orientation in which a long square bar floats in a very dramatic way.
DESCRIPTION: A long square bar floats in a bath of methyl alcohol, with its sides horizontal and vertical, as shown in the photograph. If water is added to the bath until the tank is almost full, the bar will rotate so that the sides are diagonal, due to the effective decrease in the density of the bar relative to the bath.
SUGGESTIONS: When you perform the demonstration, don't tell the students that the original bath is alcohol. Mumble something about adding "more water" to the bath, while watching the bar rotate as water is added. Discuss concepts of the center of mass, the center of buoyancy, and the stability of boats.
REFERENCES: (PIRA 2B40.56) See Demonstration Reference File for everything you ever wanted to know and more dealing with the stability of the floating square bar and other geometrical objects.
EQUIPMENT: Long square bar with alcohol tank, water tank with siphon hose.
SETUP TIME: 10 min.
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