Bone Stress

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In this optics activity, learners examine how polarized light can reveal stress patterns in clear plastic. Learners place a fork between two pieces of polarizing material and induce stress by squeezing the tines together. Learners will observe the colored stress pattern in the image of the plastic that is projected onto a screen using an overhead projector. Learners rotate one of the polarizing filters to explore which orientations give the most dramatic color effects. This activity can be related to bones, as bones develop stress patterns from the loads imposed upon them every day.

Quick Guide

Preparation Time:
10 to 30 minutes

Learning Time:
5 to 10 minutes

Estimated Materials Cost:
$5 - $10 per group of students

Age Range:
Ages 8 - 18

Resource Types:
Activity, Demonstration


Materials List (per group of students)

  • Overhead projector and screen
  • 2 polarizing filters (If polarizing material is not readily available, you can use two lenses from an old pair of polarizing sunglasses)
  • A transparent plastic picnic fork, or thin pieces of transparent plastic (Plastic from cassette tape cases works well)


  • Life Sciences
    • Human Body
      • Skeleton
  • Physical Sciences
    • Vibration and Waves
      • Wave Properties
    • Light and Optics
      • Lenses and Mirrors
      • Electromagnetic Spectrum
      • Sunlight and Color
    • Motion and Forces


To use this activity, learners need to:

  • see
  • see color

Learning styles supported:

  • Involves hands-on or lab activities


This resource is part of:

Access Rights:

  • Free access



Funding Sources:

  • National Science Foundation
  • California Department of Education
  • NEC Foundation of America