Archimedes' principle: Cup and plug on balance beam.

Archimede's principle: Cup and plug on balance beam. Step 1: Cylindrical cup containing a very close-fitting metal cylindrical plug is balanced on the equal-arm balance. Step 2: Metal plug is removed from cup and suspended from hook at bottom of cup. No change in the balance. Step 3: A beaker of water is raised to submerge the metal plug. System is unbalanced due to the bouyant force of the water. Step 4: Water is added to the cylindrical cup. When cup is filled, the balance of the system is restored. Note: Lift beam off of knife edge with knob while making changes.