PURPOSE: To demonstrate the increase of friction between two glass surfaces when lubricating surface films are removed.
DESCRIPTION: Initially, the drinking glass can be pulled across the glass plate easily and quietly. If water with detergent is applied to the plate, the greasy surface films are removed and the glass-to-glass contact is improved. As a result, friction is increased and loud squeaking noises are produced as the drinking glass is pulled across the plate.
REFERENCES: (PIRA unavailable.)
EQUIPMENT: Glass plate, drinking glass, string, detergent, water, brush and rag.
SETUP TIME: 5 min.
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