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Deformation of Solids

Stress, strain and the Young modulus

  • 3 things to know
  • Unit A2 1

Overview

Tensile stress and give its equation, tensile strain and give its equation and young modulus.

What you need to know

Answer each one before you reveal it.

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Key term

Define tensile stress and give its equation.

Key term

Give the SI unit of stress and an equivalent form of it.

Key term

Define tensile strain and give its equation.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Define tensile stress and give its equation.

    Model answer

    Tensile stress is the force applied per unit cross-sectional area, σ = F/A, where σ is the stress in Pa, F the force in newtons and A the cross-sectional area in m².

  2. 2

    Give the SI unit of stress and an equivalent form of it.

    Model answer

    Stress is measured in pascals, Pa, which is the same as N m⁻².

  3. 3

    Define tensile strain and give its equation.

    Model answer

    Tensile strain is the extension per unit original length, ε = x/l, where x is the extension in metres and l the original length in metres.

  4. 4

    Why does strain have no unit?

    Model answer

    Strain is a length divided by a length, so the units cancel and it is a pure number, often quoted as a percentage.

  5. 5

    Define the Young modulus.

    Model answer

    The Young modulus is the ratio of tensile stress to tensile strain for a material obeying Hooke's law, E = σ/ε, where E is in Pa.

  6. 6

    Express the Young modulus in terms of force, extension, cross-sectional area and original length.

    Model answer

    E = Fl/(Ax), where F is the force in N, l the original length in m, A the cross-sectional area in m² and x the extension in m.

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