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Thermal expansion
Beginner
Materials expand when heated.
ΔL = αLΔTMost materials expand when heated: ΔL = αLΔT, with α about 10⁻⁵ K⁻¹ for metals. Gaps are left in bridges and railway lines.
A 100 m steel rail (α = 12×10⁻⁶) heated by 30 K grows 3.6 cm.
Holes expand too, like the material around them.
In more detail
Most materials expand when heated, because their atoms vibrate more and sit farther apart. The linear expansion is ΔL = αLΔT, where α is the coefficient of linear expansion.
Real-world uses
- Bridges have expansion joints to allow for thermal expansion.
- Railway tracks are laid with small gaps to prevent buckling in heat.
- Engineers leave gaps between sections of railway tracks and bridges to allow for thermal expansion on hot days.
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Frequently asked questions
Why do gaps exist in bridges?
To accommodate expansion in summer and contraction in winter.
Do all materials expand?
Most do, but water is a notable exception between 0 and 4 degrees Celsius.
Why do bridges have expansion joints?
Steel expands and contracts with temperature, so the joints let the bridge change length without cracking.
Related topics in Heat & Thermodynamics
Temperature scales · Thermometers · Zeroth law · Area and volume expansion · Anomalous expansion of water · Heat