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Homework Help: Hooke's Law

  1. Jul 24, 2010 #1
    Just a quick question:

    I was wondering whether the Force Applied to a spring equates to the stress and whether the Displacement of a spring equates to the strain.

    I have been researching this on the internet and the units of stress are completely different to Force Applied and the same for displacement and strain. Thus, I have been wondering whether they mean the same thing or whether I will have to do conversions?

    Thank you very much for your help.

    Also, is Young's Modulus or the Elastic Modulus the constant of a stress vs. strain graph or Force vs. Displacement because I read on a website it is measured in GPa and I was under the impression that the Elastic Modulus had no units.
  2. jcsd
  3. Jul 24, 2010 #2


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    Homework Helper

    If by 'equates', you mean similar then yes technically.

    Stress = Force/Area (Units of N/m2 or Pa)

    Strain = extension/Length (has no units)

    So the graph would look the same essentially.

    Well I showed you above the formulas and how the quantities relate to each other.

    Young's modulus = Stress/Strain so its units would be N/m2 or Pa

    Within the elastic region is Young's Modulus constant.
  4. Jul 24, 2010 #3
    Back in the 19th century, many people used force and stress interchangeably, but by the 20th century, stress was well-defined as force per unit area. Strain is an example of a non-dimensional quantity, as is stress/Young's modulus. These non-dimensional quantities are useful ways of extending the application of experimental results to objects not tested. Hooke would have said that load is proportional to displacement, but the modern approach of stress v strain is more useful.
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