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Hooke's Law

Mechanics of Materials · FE Reference Handbook section

Mechanics of Materials
19 formulas
10 exam-style examples
~60 min
All Mechanics of Materials lectures

Handbook notes for this section

Definitions and conditions exactly as the handbook states them.

  • When there is a temperature change from an initial temperature Ti to a final temperature Tf there are also thermally-induced

Core formulas for this FE topic

Definitions, applicability, units, assumptions and worked examples for each relation.

Worked exam-style examples

The four ways this section is written on the real exam — thoughts first, then equations, then substitution.

Example 1
Hooke's law (axial) — solve for normal stress — Hooke's Law

A steel tension coupon obeys Hooke's law up to the yield point. Given modulus of elasticity (E) = 14,900 ksi; axial strain (epsilon) = 0.0002, determine the normal stress (sigma) in ksi.

Given

  • modulusofelasticity(E)=14,900ksimodulus of elasticity (E) = 14,900 ksi
  • axialstrain(epsilon)=0.0002axial strain (epsilon) = 0.0002

Find

normal stress (sigma), in ksi

Start with the thinking

  • The governing relation printed in this handbook section is Hooke's law (axial).
  • Everything except sigma is given, so isolate sigma symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Hooke's law states that stress is proportional to strain within the elastic limit of the material.
Axial tension barPAL

Figure 1 — schematic for Hooke's law (axial) — solve for normal stress — Hooke's Law

Step-by-step solution

  1. Step 1 — State the governing relation:

    σ=Eε\sigma = E \varepsilon
  2. Step 2 — Rearrange symbolically for sigma:

    σ=Eε\sigma = E \varepsilon
  3. Step 3

    Listthegivens:modulusofelasticity(E)=14,900ksi,axialstrain(epsilon)=0.0002List the givens: modulus of elasticity (E) = 14,900 ksi, axial strain (epsilon) = 0.0002
  4. Step 4 — Substitute the given values:

    σ=14900ε\sigma = 14900 \varepsilon
  5. Step 5 — Evaluate:

    σ=2.9800 ksi\sigma = 2.9800\ \text{ksi}
  6. Step 6 — Check: returning sigma = 2.9800 ksi to

    σ=Eε\sigma = E \varepsilon

    reproduces the given quantities, and both sides carry the same units.

Answer:
σ=2.9800 ksi\sigma = 2.9800\ \text{ksi}

Why the other options are there

  • 5.9600 — kept a factor of two that cancels in the correct rearrangement.
  • 1.4900 — dropped that same factor in the other direction.
  • 3.2780 — rounded an intermediate value before the final step.

Reference: FE Handbook — Mechanics of Materials: Hooke's Law

Example 2
Hooke's law (axial) — solve for modulus of elasticity — Hooke's Law (2)

An aluminum tie rod's elongation is predicted using Hooke's law. Given axial strain (epsilon) = 0.0014; normal stress (sigma) = 62.7000 ksi, determine the modulus of elasticity (E) in ksi.

Given

  • axialstrain(epsilon)=0.0014axial strain (epsilon) = 0.0014
  • normalstress(sigma)=62.7000ksinormal stress (sigma) = 62.7000 ksi

Find

modulus of elasticity (E), in ksi

Start with the thinking

  • The governing relation printed in this handbook section is Hooke's law (axial).
  • Everything except E is given, so isolate E symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Hooke's law states that stress is proportional to strain within the elastic limit of the material.
Axial tension barPAL

Figure 2 — schematic for Hooke's law (axial) — solve for modulus of elasticity — Hooke's Law (2)

Step-by-step solution

  1. Step 1 — State the governing relation:

    σ=Eε\sigma = E \varepsilon
  2. Step 2 — Rearrange symbolically for E:

    E=σεE = \dfrac{\sigma}{\varepsilon}
  3. Step 3

    Listthegivens:axialstrain(epsilon)=0.0014,normalstress(sigma)=62.7000ksiList the givens: axial strain (epsilon) = 0.0014, normal stress (sigma) = 62.7000 ksi
  4. Step 4 — Substitute the given values:

    E=62.7000εE = \dfrac{62.7000}{\varepsilon}
  5. Step 5 — Evaluate:

    E=44786 ksiE = 44786\ \text{ksi}
  6. Step 6 — Check: returning E = 44,786 ksi to

    σ=Eε\sigma = E \varepsilon

    reproduces the given quantities, and both sides carry the same units.

Answer:
E=44786 ksiE = 44786\ \text{ksi}

Why the other options are there

  • 89,571 — kept a factor of two that cancels in the correct rearrangement.
  • 22,393 — dropped that same factor in the other direction.
  • 49,264 — rounded an intermediate value before the final step.

Reference: FE Handbook — Mechanics of Materials: Hooke's Law

Example 3
Hooke's law (axial) — solve for axial strain — Hooke's Law (3)

A structural cable's stress-strain response follows Hooke's law under service load. Given modulus of elasticity (E) = 29,300 ksi; normal stress (sigma) = 23.6000 ksi, determine the axial strain (epsilon).

Given

  • modulusofelasticity(E)=29,300ksimodulus of elasticity (E) = 29,300 ksi
  • normalstress(sigma)=23.6000ksinormal stress (sigma) = 23.6000 ksi

Find

axial strain (epsilon)

Start with the thinking

  • The governing relation printed in this handbook section is Hooke's law (axial).
  • Everything except epsilon is given, so isolate epsilon symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Hooke's law states that stress is proportional to strain within the elastic limit of the material.
Axial tension barPAL

Figure 3 — schematic for Hooke's law (axial) — solve for axial strain — Hooke's Law (3)

Step-by-step solution

  1. Step 1 — State the governing relation:

    σ=Eε\sigma = E \varepsilon
  2. Step 2 — Rearrange symbolically for epsilon:

    ϵ=σE\epsilon = \dfrac{\sigma}{E}
  3. Step 3

    Listthegivens:modulusofelasticity(E)=29,300ksi,normalstress(sigma)=23.6000ksiList the givens: modulus of elasticity (E) = 29,300 ksi, normal stress (sigma) = 23.6000 ksi
  4. Step 4 — Substitute the given values:

    ϵ=23.600029300\epsilon = \dfrac{23.6000}{29300}
  5. Step 5 — Evaluate:

    ϵ=0.0008\epsilon = 0.0008
  6. Step 6 — Check: returning epsilon = 0.0008 to

    σ=Eε\sigma = E \varepsilon

    reproduces the given quantities, and both sides carry the same units.

Answer:
ϵ=0.0008\epsilon = 0.0008

Why the other options are there

  • 0.0016 — kept a factor of two that cancels in the correct rearrangement.
  • 0.0004 — dropped that same factor in the other direction.
  • 0.0009 — rounded an intermediate value before the final step.

Reference: FE Handbook — Mechanics of Materials: Hooke's Law

Example 4
Hooke's law (axial) — solve for normal stress (case 2) — Hooke's Law (4)

A steel tension coupon obeys Hooke's law up to the yield point. Given modulus of elasticity (E) = 25,000 ksi; axial strain (epsilon) = 0.0020, determine the normal stress (sigma) in ksi.

Given

  • modulusofelasticity(E)=25,000ksimodulus of elasticity (E) = 25,000 ksi
  • axialstrain(epsilon)=0.0020axial strain (epsilon) = 0.0020

Find

normal stress (sigma), in ksi

Start with the thinking

  • The governing relation printed in this handbook section is Hooke's law (axial).
  • Everything except sigma is given, so isolate sigma symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Hooke's law states that stress is proportional to strain within the elastic limit of the material.
Axial tension barPAL

Figure 4 — schematic for Hooke's law (axial) — solve for normal stress (case 2) — Hooke's Law (4)

Step-by-step solution

  1. Step 1 — State the governing relation:

    σ=Eε\sigma = E \varepsilon
  2. Step 2 — Rearrange symbolically for sigma:

    σ=Eε\sigma = E \varepsilon
  3. Step 3

    Listthegivens:modulusofelasticity(E)=25,000ksi,axialstrain(epsilon)=0.0020List the givens: modulus of elasticity (E) = 25,000 ksi, axial strain (epsilon) = 0.0020
  4. Step 4 — Substitute the given values:

    σ=25000ε\sigma = 25000 \varepsilon
  5. Step 5 — Evaluate:

    σ=50.0000 ksi\sigma = 50.0000\ \text{ksi}
  6. Step 6 — Check: returning sigma = 50.0000 ksi to

    σ=Eε\sigma = E \varepsilon

    reproduces the given quantities, and both sides carry the same units.

Answer:
σ=50.0000 ksi\sigma = 50.0000\ \text{ksi}

Why the other options are there

  • 100.0 — kept a factor of two that cancels in the correct rearrangement.
  • 25.0000 — dropped that same factor in the other direction.
  • 55.0000 — rounded an intermediate value before the final step.

Reference: FE Handbook — Mechanics of Materials: Hooke's Law

Example 5
Hooke's law (axial) — solve for modulus of elasticity (case 2) — Hooke's Law (5)

An aluminum tie rod's elongation is predicted using Hooke's law. Given axial strain (epsilon) = 0.0014; normal stress (sigma) = 75.3000 ksi, determine the modulus of elasticity (E) in ksi.

Given

  • axialstrain(epsilon)=0.0014axial strain (epsilon) = 0.0014
  • normalstress(sigma)=75.3000ksinormal stress (sigma) = 75.3000 ksi

Find

modulus of elasticity (E), in ksi

Start with the thinking

  • The governing relation printed in this handbook section is Hooke's law (axial).
  • Everything except E is given, so isolate E symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Hooke's law states that stress is proportional to strain within the elastic limit of the material.
Axial tension barPAL

Figure 5 — schematic for Hooke's law (axial) — solve for modulus of elasticity (case 2) — Hooke's Law (5)

Step-by-step solution

  1. Step 1 — State the governing relation:

    σ=Eε\sigma = E \varepsilon
  2. Step 2 — Rearrange symbolically for E:

    E=σεE = \dfrac{\sigma}{\varepsilon}
  3. Step 3

    Listthegivens:axialstrain(epsilon)=0.0014,normalstress(sigma)=75.3000ksiList the givens: axial strain (epsilon) = 0.0014, normal stress (sigma) = 75.3000 ksi
  4. Step 4 — Substitute the given values:

    E=75.3000εE = \dfrac{75.3000}{\varepsilon}
  5. Step 5 — Evaluate:

    E=53786 ksiE = 53786\ \text{ksi}
  6. Step 6 — Check: returning E = 53,786 ksi to

    σ=Eε\sigma = E \varepsilon

    reproduces the given quantities, and both sides carry the same units.

Answer:
E=53786 ksiE = 53786\ \text{ksi}

Why the other options are there

  • 107,571 — kept a factor of two that cancels in the correct rearrangement.
  • 26,893 — dropped that same factor in the other direction.
  • 59,164 — rounded an intermediate value before the final step.

Reference: FE Handbook — Mechanics of Materials: Hooke's Law

Example 6
Hooke's law (axial) — solve for axial strain (case 2) — Hooke's Law (6)

A structural cable's stress-strain response follows Hooke's law under service load. Given modulus of elasticity (E) = 24,800 ksi; normal stress (sigma) = 56.4000 ksi, determine the axial strain (epsilon).

Given

  • modulusofelasticity(E)=24,800ksimodulus of elasticity (E) = 24,800 ksi
  • normalstress(sigma)=56.4000ksinormal stress (sigma) = 56.4000 ksi

Find

axial strain (epsilon)

Start with the thinking

  • The governing relation printed in this handbook section is Hooke's law (axial).
  • Everything except epsilon is given, so isolate epsilon symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Hooke's law states that stress is proportional to strain within the elastic limit of the material.
Axial tension barPAL

Figure 6 — schematic for Hooke's law (axial) — solve for axial strain (case 2) — Hooke's Law (6)

Step-by-step solution

  1. Step 1 — State the governing relation:

    σ=Eε\sigma = E \varepsilon
  2. Step 2 — Rearrange symbolically for epsilon:

    ϵ=σE\epsilon = \dfrac{\sigma}{E}
  3. Step 3

    Listthegivens:modulusofelasticity(E)=24,800ksi,normalstress(sigma)=56.4000ksiList the givens: modulus of elasticity (E) = 24,800 ksi, normal stress (sigma) = 56.4000 ksi
  4. Step 4 — Substitute the given values:

    ϵ=56.400024800\epsilon = \dfrac{56.4000}{24800}
  5. Step 5 — Evaluate:

    ϵ=0.0023\epsilon = 0.0023
  6. Step 6 — Check: returning epsilon = 0.0023 to

    σ=Eε\sigma = E \varepsilon

    reproduces the given quantities, and both sides carry the same units.

Answer:
ϵ=0.0023\epsilon = 0.0023

Why the other options are there

  • 0.0045 — kept a factor of two that cancels in the correct rearrangement.
  • 0.0011 — dropped that same factor in the other direction.
  • 0.0025 — rounded an intermediate value before the final step.

Reference: FE Handbook — Mechanics of Materials: Hooke's Law

Example 7
Hooke's law (axial) — solve for normal stress (case 3) — Hooke's Law (7)

A steel tension coupon obeys Hooke's law up to the yield point. Given modulus of elasticity (E) = 19,100 ksi; axial strain (epsilon) = 0.0016, determine the normal stress (sigma) in ksi.

Given

  • modulusofelasticity(E)=19,100ksimodulus of elasticity (E) = 19,100 ksi
  • axialstrain(epsilon)=0.0016axial strain (epsilon) = 0.0016

Find

normal stress (sigma), in ksi

Start with the thinking

  • The governing relation printed in this handbook section is Hooke's law (axial).
  • Everything except sigma is given, so isolate sigma symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Hooke's law states that stress is proportional to strain within the elastic limit of the material.
Axial tension barPAL

Figure 7 — schematic for Hooke's law (axial) — solve for normal stress (case 3) — Hooke's Law (7)

Step-by-step solution

  1. Step 1 — State the governing relation:

    σ=Eε\sigma = E \varepsilon
  2. Step 2 — Rearrange symbolically for sigma:

    σ=Eε\sigma = E \varepsilon
  3. Step 3

    Listthegivens:modulusofelasticity(E)=19,100ksi,axialstrain(epsilon)=0.0016List the givens: modulus of elasticity (E) = 19,100 ksi, axial strain (epsilon) = 0.0016
  4. Step 4 — Substitute the given values:

    σ=19100ε\sigma = 19100 \varepsilon
  5. Step 5 — Evaluate:

    σ=30.5600 ksi\sigma = 30.5600\ \text{ksi}
  6. Step 6 — Check: returning sigma = 30.5600 ksi to

    σ=Eε\sigma = E \varepsilon

    reproduces the given quantities, and both sides carry the same units.

Answer:
σ=30.5600 ksi\sigma = 30.5600\ \text{ksi}

Why the other options are there

  • 61.1200 — kept a factor of two that cancels in the correct rearrangement.
  • 15.2800 — dropped that same factor in the other direction.
  • 33.6160 — rounded an intermediate value before the final step.

Reference: FE Handbook — Mechanics of Materials: Hooke's Law

Example 8
Hooke's law (axial) — solve for modulus of elasticity (case 3) — Hooke's Law (8)

An aluminum tie rod's elongation is predicted using Hooke's law. Given axial strain (epsilon) = 0.0008; normal stress (sigma) = 80.0000 ksi, determine the modulus of elasticity (E) in ksi.

Given

  • axialstrain(epsilon)=0.0008axial strain (epsilon) = 0.0008
  • normalstress(sigma)=80.0000ksinormal stress (sigma) = 80.0000 ksi

Find

modulus of elasticity (E), in ksi

Start with the thinking

  • The governing relation printed in this handbook section is Hooke's law (axial).
  • Everything except E is given, so isolate E symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Hooke's law states that stress is proportional to strain within the elastic limit of the material.
Axial tension barPAL

Figure 8 — schematic for Hooke's law (axial) — solve for modulus of elasticity (case 3) — Hooke's Law (8)

Step-by-step solution

  1. Step 1 — State the governing relation:

    σ=Eε\sigma = E \varepsilon
  2. Step 2 — Rearrange symbolically for E:

    E=σεE = \dfrac{\sigma}{\varepsilon}
  3. Step 3

    Listthegivens:axialstrain(epsilon)=0.0008,normalstress(sigma)=80.0000ksiList the givens: axial strain (epsilon) = 0.0008, normal stress (sigma) = 80.0000 ksi
  4. Step 4 — Substitute the given values:

    E=80.0000εE = \dfrac{80.0000}{\varepsilon}
  5. Step 5 — Evaluate:

    E=100000 ksiE = 100000\ \text{ksi}
  6. Step 6 — Check: returning E = 100,000 ksi to

    σ=Eε\sigma = E \varepsilon

    reproduces the given quantities, and both sides carry the same units.

Answer:
E=100000 ksiE = 100000\ \text{ksi}

Why the other options are there

  • 200,000 — kept a factor of two that cancels in the correct rearrangement.
  • 50,000 — dropped that same factor in the other direction.
  • 110,000 — rounded an intermediate value before the final step.

Reference: FE Handbook — Mechanics of Materials: Hooke's Law

Example 9
Hooke's law (axial) — solve for axial strain (case 3) — Hooke's Law (9)

A structural cable's stress-strain response follows Hooke's law under service load. Given modulus of elasticity (E) = 29,000 ksi; normal stress (sigma) = 54.9000 ksi, determine the axial strain (epsilon).

Given

  • modulusofelasticity(E)=29,000ksimodulus of elasticity (E) = 29,000 ksi
  • normalstress(sigma)=54.9000ksinormal stress (sigma) = 54.9000 ksi

Find

axial strain (epsilon)

Start with the thinking

  • The governing relation printed in this handbook section is Hooke's law (axial).
  • Everything except epsilon is given, so isolate epsilon symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Hooke's law states that stress is proportional to strain within the elastic limit of the material.
Axial tension barPAL

Figure 9 — schematic for Hooke's law (axial) — solve for axial strain (case 3) — Hooke's Law (9)

Step-by-step solution

  1. Step 1 — State the governing relation:

    σ=Eε\sigma = E \varepsilon
  2. Step 2 — Rearrange symbolically for epsilon:

    ϵ=σE\epsilon = \dfrac{\sigma}{E}
  3. Step 3

    Listthegivens:modulusofelasticity(E)=29,000ksi,normalstress(sigma)=54.9000ksiList the givens: modulus of elasticity (E) = 29,000 ksi, normal stress (sigma) = 54.9000 ksi
  4. Step 4 — Substitute the given values:

    ϵ=54.900029000\epsilon = \dfrac{54.9000}{29000}
  5. Step 5 — Evaluate:

    ϵ=0.0019\epsilon = 0.0019
  6. Step 6 — Check: returning epsilon = 0.0019 to

    σ=Eε\sigma = E \varepsilon

    reproduces the given quantities, and both sides carry the same units.

Answer:
ϵ=0.0019\epsilon = 0.0019

Why the other options are there

  • 0.0038 — kept a factor of two that cancels in the correct rearrangement.
  • 0.0009 — dropped that same factor in the other direction.
  • 0.0021 — rounded an intermediate value before the final step.

Reference: FE Handbook — Mechanics of Materials: Hooke's Law

Example 10
Hooke's law (axial) — solve for normal stress (case 4) — Hooke's Law (10)

A steel tension coupon obeys Hooke's law up to the yield point. Given modulus of elasticity (E) = 13,000 ksi; axial strain (epsilon) = 0.0019, determine the normal stress (sigma) in ksi.

Given

  • modulusofelasticity(E)=13,000ksimodulus of elasticity (E) = 13,000 ksi
  • axialstrain(epsilon)=0.0019axial strain (epsilon) = 0.0019

Find

normal stress (sigma), in ksi

Start with the thinking

  • The governing relation printed in this handbook section is Hooke's law (axial).
  • Everything except sigma is given, so isolate sigma symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Hooke's law states that stress is proportional to strain within the elastic limit of the material.
Axial tension barPAL

Figure 10 — schematic for Hooke's law (axial) — solve for normal stress (case 4) — Hooke's Law (10)

Step-by-step solution

  1. Step 1 — State the governing relation:

    σ=Eε\sigma = E \varepsilon
  2. Step 2 — Rearrange symbolically for sigma:

    σ=Eε\sigma = E \varepsilon
  3. Step 3

    Listthegivens:modulusofelasticity(E)=13,000ksi,axialstrain(epsilon)=0.0019List the givens: modulus of elasticity (E) = 13,000 ksi, axial strain (epsilon) = 0.0019
  4. Step 4 — Substitute the given values:

    σ=13000ε\sigma = 13000 \varepsilon
  5. Step 5 — Evaluate:

    σ=24.7000 ksi\sigma = 24.7000\ \text{ksi}
  6. Step 6 — Check: returning sigma = 24.7000 ksi to

    σ=Eε\sigma = E \varepsilon

    reproduces the given quantities, and both sides carry the same units.

Answer:
σ=24.7000 ksi\sigma = 24.7000\ \text{ksi}

Why the other options are there

  • 49.4000 — kept a factor of two that cancels in the correct rearrangement.
  • 12.3500 — dropped that same factor in the other direction.
  • 27.1700 — rounded an intermediate value before the final step.

Reference: FE Handbook — Mechanics of Materials: Hooke's Law

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