Stress, Strain and the Young Modulus · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Stress, strain, and true stiffness

Science · Matter & Materials · ages 17-18
Name ______________________   Date ____________

  1. What are the units of strain?

    • No units at all
    • Pascals
    • Newtons

  2. What is stress?

    • Extension over length
    • Force times area
    • Force over area

  3. Strain is measured in metres.

    Circle one:   True   False

  4. A 2 m wire stretches by 0.001 m. What is the strain?

    Answer: ______________

  5. A 100 N load pulls a wire of cross section 0.000002 square metres. What is the stress in pascals?

    Answer: ______________

  6. What is the Young modulus, and what is its unit?

    • Strain over stress, in newtons
    • Stress over strain, in pascals
    • Force over extension, in joules

  7. A thin wire and a thick rod of steel share one modulus. Why?

    • The rod was tested gently
    • Steel samples all have equal area
    • Area and extension shift together, leaving the ratio fixed

  8. A wire carries stress 50000000 Pa at strain 0.0005. What is its Young modulus in pascals?

    Answer: ______________

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Answer key

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Stress, strain, and true stiffness W1-mt_uWdqhWGT7Y-s1

  1. No units at all · Strain divides extension by length, so the units cancel out.
  2. Force over area · Stress spreads the force over the cross section, in pascals.
  3. False · Strain is a ratio of two lengths, so it carries no units.
  4. 0.0005 · Divide extension by length: 0.001 over 2 is 0.0005, with no units.
  5. 50000000 · Divide force by area: 100 over 0.000002 is 50000000 pascals.
  6. Stress over strain, in pascals · The straight-line gradient of stress against strain is the modulus, in pascals.
  7. Area and extension shift together, leaving the ratio fixed · Doubling the area halves the stress while strain follows suit, so the ratio is untouched.
  8. 100000000000 · Divide stress by strain: 50000000 over 0.0005 is 100000000000 pascals.
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