this experiment enables you to see stresses in plastic objects. you need some plastic objects, a source of white light and two polarized lenses. now here is an ordinary source of white light
and here is some butter paper. the butter paper is kept on white light to diffuse the
white light. we also need a pair of polarized lenses which you can get from 3D glasses.
now these are bipolar lenses, if you rotate them they polarize light. now place a plastic
scale on top of one lens. now this limits the vibrations of light and place the second
lens on top and see beautiful beautiful colored lines and these are stress lines. as you rotate
the upper lens you can see very beautiful stress lines at cuts, at joints, at bends,
you see there are more stresses. the faster the change in color more the stress inside
the object. you can repeat this experiment with a transparent CD. place it between two
polarized lenses and you can see extremely beautiful stress patterns as you rotate the
top lens. now this is the fun with polarized light that you are actually able to see stresses
in objects and which tells you the points where they are much more likely to break.