Stress, Strain and Hooke's Law
Students explore Hooke's LawCopyright Oleg Alexandrov, Wikimedia Commons
Students are introduced to Hooke's law as well as stress-strain relationships. First they learn the governing equations, then they work through several example problems, first individually, then as a class. Through the lesson's two-part associated activity, students 1) explore Hooke's law by experimentally determining an unknown spring constant, and then 2) apply what they've learned to create a strain graph depicting a tumor using Microsoft Excel®. After the activities, the lesson concludes with a stress-strain quiz to assess each student's comprehension of the concepts.
More than 300 years ago, Robert Hooke identified a proportionality that has remained a fundamental concept to physicists and engineers to this day. Though his "law" was established for the case of springs alone, it has since been related to all materials of known surface area. The relationship used most readily today is the direct proportionality between stress and strain. Together, civil engineers, mechanical engineers and material scientists, carefully select structural materials that are able to safely endure everyday stress while remaining in the elastic region of the stress-strain curve, otherwise permanent deformation occurs. Architects who once chose stone for its aesthetic appeal now choose steel for its long-term endurance. For biomedical engineers, titanium is often the material of choice for its biocompatibility and more importantly, its capability to withstand the tensile and compressive stress of the body's weight. In the provided problem set, students explore applications of Hooke's law and stress-strain relationships. In problem 7 especifically, students apply these relationships to the case of body tissue, as biomedical engineers would.
After this lesson, students should be able to:
- Explain the stress and strain concepts and the relationship between them.
- Explain Hooke's law and apply it to analyze springs.
- Use Microsoft Excel® to make a simple strain plot.
- Relate stress and strain to the unit's engineering challenge.