A steel car body panel is stamped into shape by a large machine press in a factory. Once the pressing force is removed, the panel keeps its new shape permanently. Explain why the panel keeps its new shape and why this behaviour is different from what would happen if the panel had only been bent slightly by a much smaller force.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
In car manufacturing, metal panels are shaped by applying very large forces to flat sheets of steel. The finished panels do not spring back to their original flat shape after the force is removed.
Model answer (4 marks)
The large force applied by the press exceeds the elastic limit of the steel, causing plastic deformation. Because the material has been plastically distorted, it does not return to its original flat shape when the force is removed.
If the panel had only been bent by a much smaller force, the stress would remain below the elastic limit. The steel would then undergo elastic deformation and would spring back to its original shape once the force was removed.
If the panel had only been bent by a much smaller force, the stress would remain below the elastic limit. The steel would then undergo elastic deformation and would spring back to its original shape once the force was removed.
Examiner tips
- Use the terms "elastic limit" and "plastic deformation"
- Explain that exceeding the elastic limit means permanent change
- Contrast with elastic deformation that is reversible
- Keep the answer concise and to the point
Common mistakes
- Confusing elastic and plastic deformation
- Using vague phrases like "stiffness" instead of "elastic limit"
- Failing to mention the permanent nature of plastic deformation
Mark scheme (4 marks)
- The large force exceeds the elastic limit of the steel
- This causes plastic distortion / plastic deformation of the steel
- So the panel does not return to its original shape when the force is removed
- A smaller force would only cause elastic distortion, so the panel would return to its original flat shape when the force was removed
Related
- All Edexcel GCSE Physics (1PH0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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