# Explain why a metal railway track has a higher thermal expansion than a wooden railway sleeper when both are heated by the same temperature rise, and state one practical consequence of thermal expansion that is accounted for in railway track design.

> Cambridge International IGCSE Physics (0625) — 2.2 Thermal properties and temperature · Explain · 4 marks

## Mark scheme (4 marks)

1. When heated, molecules (in both materials) vibrate more / take up more space
2. Metals / the rail expand more than wood because the intermolecular forces in metal allow greater expansion / metals expand more for the same temperature rise (accept: different materials have different rates/amounts of thermal expansion)
3. Small gaps are left between sections of railway track
4. So that the track does not buckle / bend when it expands (in warm weather / when heated)

## Key terms

- [thermal expansion](https://www.gradenine.co.uk/glossary/thermal-expansion)

## Related

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