PURPOSE: To present buoyancy in a paradoxical way.
DESCRIPTION: The balance is initially at equilibrium with a mass hanging from an arm on the left pan. The left pan has two weights plus the arm supporting the 50 cm^3 hanging block, which is in balance with the water beaker on the right pan. Q: If the mass is allowed to hang into the beaker of water, how does this effect the balance? In particular, what, if anything must be done to restore equilibrium? A: Because the volume of the volume of the block is 50 cm^3, the weight on the left side is reduced by 50 grams when the block is submerged in the water. Conversely, the weight on the right side is increased by 50 grams, the reaction force on that pan. To recreate balance, 100 grams must be added to the left pan.
SUGGESTIONS: Ask the class to discuss this one!
REFERENCES: (PIRA unavailable.)
EQUIPMENT: Pan balance, weights, beaker with water, boom with hanging weight.
SETUP TIME: 5 min.
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