# A steel cable used to support a suspension bridge is stretched by a large tensile force. Explain how stress, strain and the Young modulus are each used to describe the behaviour of the cable under this force, and state what the Young modulus tells an engineer about the cable material.

> Edexcel A-Level Physics (9PH0) — 4.1 Stress, strain and the Young modulus · Explain · 5 marks

> Engineers selecting materials for a suspension bridge must consider how the cables will respond to large tensile forces. Steel is chosen because of its mechanical properties under stress.

## Mark scheme (5 marks)

1. Stress is defined as the force applied divided by the cross-sectional area of the cable
2. Strain is the fractional extension — the extension of the cable divided by its original length
3. The Young modulus is the ratio of stress to strain (stress divided by strain)
4. The Young modulus is a measure of the stiffness of the material
5. A high Young modulus for steel means the cable will only deform (stretch) by a small amount under large stress, making it suitable for the bridge

## Key terms

- [stress](https://www.gradenine.co.uk/glossary/stress)
- [strain](https://www.gradenine.co.uk/glossary/strain)
- [Young modulus](https://www.gradenine.co.uk/glossary/young-modulus)
- [tensile force](https://www.gradenine.co.uk/glossary/tensile-force)

## Related

- [Revision notes for Edexcel A-Level Physics (9PH0)](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-steel-cable-used-to-support-65a9a578) · Published by Druglandscape Ltd.