PURPOSE: To demonstrate photoelasticity in plastic.

DESCRIPTION: The system of mounted rotating polaroids in front of a goose neck lamp is used with various stress samples for this demonstration. Rotating either polaroid shows how polaroids work. With the two polarizers crossed, a U-shaped piece of plastic is held between the two crossed polaroids (left) and squeezed at its ends to produce stress patterns (right) with varied colors and intensities. A plastic sheet (provided) can be stretched or a McDonald's plastic salad bar container stressed during manufacture (also provided) can be positioned between the polaroids to show similar patterns.

SUGGESTIONS:

REFERENCES: (PIRA 6H35.50, 6H35.55)

EQUIPMENT: Mounted polaroid sheets with goose neck lamp, plastic U, plastic sheet, plastic salad container.

SETUP TIME: None.