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Young's Modulus

conceptmedium~20 min study9 MCQ

The ratio of longitudinal stress to longitudinal strain within the elastic limit, representing a material's resistance to stretching or compression.

What is Young's Modulus?

A measure of the stiffness of an elastic material, equal to the ratio of the longitudinal stress to the longitudinal strain within the elastic limit.

Key formula / rule: Young's Modulus

Key points

  • Define Young's modulus and its significance.
  • State the formula for Young's modulus.
  • Calculate Young's modulus given stress and strain values.
  • Relate Young's modulus to the stiffness of a material.

Common exam trap

Confusing longitudinal stress/strain with shear stress/strain or bulk stress/strain.

Definitions

Term

Young's Modulus (Y)

Meaning

A measure of the stiffness of an elastic material, equal to the ratio of the longitudinal stress to the longitudinal strain within the elastic limit.

Term

Longitudinal Stress

Meaning

The force applied per unit cross-sectional area that tends to stretch or compress an object along its length.

Term

Longitudinal Strain

Meaning

The fractional change in length of an object when subjected to longitudinal stress; defined as the change in length divided by the original length.

Term

Elastic Limit

Meaning

The maximum stress that a material can withstand without permanent deformation. Beyond this limit, the material may not return to its original shape after the stress is removed.

Learning objectives

  • Define Young's modulus and its significance.

  • State the formula for Young's modulus.

  • Calculate Young's modulus given stress and strain values.

  • Relate Young's modulus to the stiffness of a material.

  • Identify the units of Young's modulus.

Formulae

Name

Young's Modulus

Note

Where σ is longitudinal stress and ε is longitudinal strain.

Expression

Y = \frac{\σ}{\varepsilon}

Name

Longitudinal Stress

Note

F is the applied force perpendicular to the cross-sectional area A.

Expression

\σ = \frac{F}{A}

Name

Longitudinal Strain

Note

ΔL is the change in length and L₀ is the original length.

Expression

\varepsilon = \frac{\Δ L}{L0}

Name

Young's Modulus (Combined)

Note

This combines the definitions of stress and strain into the Young's modulus formula.

Expression

Y = \frac{F/A}{\Δ L/L0} = \frac{F L0}{A \Δ L}

Prerequisites

  • Understanding of Force and Pressure.

  • Concept of Strain (linear/longitudinal).

  • Understanding of Elasticity and Elastic Limit.

  • Basic algebra for formula manipulation.

Common mistakes

  • Confusing longitudinal stress/strain with shear stress/strain or bulk stress/strain.

  • Applying the formula beyond the elastic limit of the material.

  • Incorrectly calculating stress (e.g., using force instead of force per area) or strain (e.g., using absolute change in length instead of fractional change).

  • Using inconsistent units for force, area, or length.

Keywords

  • Young's Modulus

  • Elasticity

  • Stress

  • Strain

  • Stiffness

  • Hooke's Law

  • Material Properties

  • Tensile Strength

  • Compressive Strength

Practice preview

  • What is Young's modulus a measure of?

    easy

  • The unit of Young's modulus is the same as the unit of:

    easy

  • A metal wire is stretched by a load. If the load is increased such that the stress exceeds the elastic limit, what happens to Young's modulus?

    medium