# A student is investigating how a spring stretches when different forces are applied to it. The student notices that at first the extension increases steadily with each added force, but then the spring starts to stretch much more for each extra force added, and eventually the spring does not return to its original length when the force is removed. Explain what is happening at each stage of this investigation, using the terms elastic deformation, plastic deformation, limit of proportionality, and Hooke's Law.

> OCR A-Level Physics A (H556) — 2.1 Physical quantities and units · Explain · 5 marks

> A student hangs increasing weights from a spring and records the extension each time. At first the spring behaves predictably, but beyond a certain point the behaviour changes, and after removing all the weights the spring is permanently longer than it was at the start.

## Mark scheme (5 marks)

1. In the first stage, the extension is directly proportional to the force applied / the spring obeys Hooke's Law
2. In the first stage, the spring undergoes elastic deformation, meaning it returns to its original shape / length when the force is removed
3. The point at which the extension is no longer directly proportional to the force is called the limit of proportionality
4. Beyond the limit of proportionality, the spring no longer obeys Hooke's Law / the extension increases more rapidly for each additional force
5. When the spring does not return to its original length after the force is removed, it has undergone plastic deformation / the deformation is permanent

## Key terms

- [Hooke's Law](https://www.gradenine.co.uk/glossary/hooke-s-law)
- [elastic deformation](https://www.gradenine.co.uk/glossary/elastic-deformation)
- [plastic deformation](https://www.gradenine.co.uk/glossary/plastic-deformation)
- [limit of proportionality](https://www.gradenine.co.uk/glossary/limit-of-proportionality)

## Related

- [Revision notes for OCR A-Level Physics A (H556)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-is-investigating-how-a-101a8770) · Published by Druglandscape Ltd.