Young's Modulus
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
