Most materials expand when heated and contract when cooled, because higher temperature makes atoms vibrate more and take up more space. For length changes, the linear thermal expansion formula is:
Formula: ΔL = α × L × ΔT — change in length = coefficient × original length × temperature change
Coefficients (approx., per °C)
| Material | α (×10⁻₆/°C) |
|---|---|
| Steel | ~12 |
| Stainless steel | ~17 |
| Aluminum | ~23 |
| Copper | ~17 |
| Concrete | ~12 |
Worked example
A 10 m steel beam heated 30°C: ΔL = 12×10⁻₆ × 10 × 30 = 0.0036 m, or 3.6 mm. It sounds small, but across bridges, rails, and pipelines it’s why expansion joints exist — without room to grow, thermal stress can buckle or crack structures.
Frequently asked questions
What’s the thermal expansion formula? ΔL = α × L × ΔT for length change.
Which expands more, aluminum or steel? Aluminum — its coefficient is about double steel’s.
Why do bridges have expansion joints? To give materials room to grow and shrink without cracking.
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