Explain why a spring that has been stretched beyond its elastic limit will not return to its original length when the force is removed.

AQA GCSE Physics (8463) — 4.5.3 Forces and elasticity · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

A spring stretched beyond its elastic limit undergoes plastic deformation, which is permanent.
The elastic limit is the maximum force at which the spring can deform and still return to its original shape.
When the applied force exceeds this limit, the internal structure of the spring changes irreversibly.
Consequently, when the force is removed the spring cannot recover its original length and remains elongated.

Examiner tips

  • Use the term "plastic deformation" and explain it is permanent.
  • Mention the elastic limit as the threshold force.
  • Show that below the limit deformation is elastic and reversible.
  • Keep the answer concise and directly address why the spring does not return.

Common mistakes

  • Confusing elastic deformation with plastic deformation.
  • Forgetting to mention the elastic limit as the threshold.
  • Stating that the spring will still return to its original length after exceeding the limit.

Mark scheme (4 marks)

  1. Stretching beyond the elastic limit causes plastic deformation
  2. Plastic deformation is permanent / the spring does not return to its original shape
  3. The elastic limit is the force beyond which an object will no longer deform elastically
  4. Below the elastic limit, deformation is elastic, meaning the spring would return to its original shape when the force is removed

Key terms in this question

elastic limit

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