EQUIPMENT
    Polaroid Filters
    Plexiglas Stress Models
   




NARRATIVE
            Place a Polaroid filter on the lecture table overhead projector. Place a glass plate over the Polaroid filter on two wooden blocks. Set the other Polaroid filter on the glass plate. Insert one of the plastic models between the two filters and notice the projected pattern. At points where strain is high, many lines are close together. There are two similar models, one which is stressed and the  other is unstressed. The stressed model was cut from a sheet of plexiglas, whereas the unstressed model was cast in its present shape.