Using Cross-sectional Area to Calculate Engineering Stress

The lesson will task students with performing three-point-flexural tests on pencils of different shapes in order to experimentally calculate the ultimate flexural strength of each pencil. The students will learn how engineers quantify the fact that the load a material can hold is dependent on its geometry. The students will bridge the gap between two desks using the pencils and then hang weights from the center of the pencils. The methods of attaching the pencils to desk, hanging the weights, and placing the weights will be left for them to design. The students will use data from their tests and mathematical formulas for stress to quantify the internal forces breaking the pencils. The formulas require calculation of the cross-sectional-area of the material being tested, which is a fundamental application of a 7th Grade Geometry standard.