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Q: If you wear polarized sunglasses while driving, you have probably noticed the large spots, usually arranged in patterns, on the rear windows of other cars. What are those spots, and why do polarized sunglasses reveal them?
A: The spots indicate stress points in the bonding of glass plates into a windowpane. The manipulation of the glass ‘stretches’ and untangles long molecules, orienting them along the direction of stretching, turning them into polarizing filters.
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