# Lesson Plan: Relating Stress to Strain Physics

This lesson plan includes the objectives, prerequisites, and exclusions of the lesson teaching students how to calculate the Young modulus of materials and the elastic potential energy of objects from values of stress and strain.

#### Objectives

Students will be able to

• recognize that tensile stress is a quantity defined as the tensile force per unit cross-sectional area of an object that a tensile force acts on,
• use the formula in all combinations,
• recognize that the unit of stress is newtons per square metre (N/m2 ), which is equivalent to the pascal,
• recognize that strain is a dimensionless quantity defined as the extension of an object divided by the unextended length of the object,
• use the formula in all combinations,
• recognize that the Young modulus of a substance is determined by the tensile stress on an object of the substance divided by the tensile strain of the object,
• use the formula ,
• recognize that Young’s modulus is typically measured using units of gigapascals,
• relate the tensile strain of an object to the elastic potential energy change resulting from the strain using the formula .

#### Prerequisites

Students should already be familiar with

• Hooke’s law,
• elastic potential energy.

#### Exclusions

Students will not cover

• microscopic representations of strained objects,
• deformation of objects other than their extension parallel to the tensile force direction,
• dependency of Young’s modulus on applied stress,
• material properties other than Young’s modulus and density.