PURPOSE: To illustrate buoyancy in a paradoxical way.

DESCRIPTION: A large styrofoam block with a smaller aluminum block mounted on top as in the picture at the left, floats with the center of the styrofoam block, marked by the black line, at the water level. Q: When this gizzit is inverted, with the aluminum block in the water, will the water level on the styrofoam block be (a) above, (b) below, or (c) at the black line? A: The water level will be below the black line, as seen by clicking your mouse on either of the pictures above. Notice also that the water level in the tank remains the same, at the level of the top of the black tape.

SUGGESTIONS: Let your students vote on this and discuss it before doing the experiment.

See Question of the Week #32 for information on using this demonstration to enhance class involvement.

REFERENCES: (PIRA unknown.)

EQUIPMENT: Styrofoam/aluminum block floater, tank of water.

SETUP TIME: 5 min.