# A glass rod and a copper rod are each subjected to increasing tensile forces. The glass rod snaps suddenly without any permanent change in shape. The copper rod changes shape permanently before eventually breaking. Describe the difference in behaviour between the two rods and use the terms brittle and ductile in your answer.

> AQA A-Level Physics (7408) — 3.4.2 Materials · Describe · 5 marks

## Mark scheme (5 marks)

1. Glass is brittle / the glass rod is brittle
2. A brittle material breaks without (significant/any) plastic deformation / without changing shape permanently
3. Copper is ductile / the copper rod is ductile
4. A ductile material can undergo plastic deformation / can be permanently stretched or drawn into a new shape before breaking
5. Both materials obey Hooke's law / behave elastically up to the limit of proportionality / elastic limit, returning to original shape if the force is removed below that point, but glass fractures at/near this limit whereas copper extends further (plastically) beyond it

## Key terms

- [brittle](https://www.gradenine.co.uk/glossary/brittle)
- [ductile](https://www.gradenine.co.uk/glossary/ductile)

## Related

- [Revision notes for AQA A-Level Physics (7408)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" 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-glass-rod-and-a-copper-c48d13d7) · Published by Druglandscape Ltd.