Definition
A number that expresses how much a given material changes in length, area, or volume for each one-degree change in temperature. Each material has its own coefficient, which is why dissimilar metals heated together expand by different amounts.
Plain English
It is a number that tells you how much a material grows when it gets hotter, or shrinks when it gets cooler, for every degree the temperature changes.
Context Anchor
Seen in aircraft maintenance and materials discussions, especially when comparing aluminum, steel, engine parts, windows, and other parts exposed to heating and cooling.
Derivation
From Latin coefficiens, 'working together with,' combined with 'thermal' (heat) and 'expansion' (spreading out). It is literally the number that 'works with' temperature to predict how much a material spreads.
Why Pilots Care
Different materials in an aircraft expand at different rates when heated. Engineers and mechanics must account for this when fitting parts together, especially around engines and exhaust systems, to prevent binding, cracking, or leaks as temperatures change.
Analogy
Think of each material as having its own tiny growth rate when it gets warmer. Aluminum and steel may both expand with heat, but not by exactly the same amount.
Grounding Statement
A steel exhaust pipe gets noticeably longer when hot and shorter when cold. The coefficient of thermal expansion is the number that predicts exactly how much.
Intuition Check
Do not read coefficient as the total amount of expansion. It is the rate of expansion for a material per degree of temperature change.
Example Sentence 1
Aluminum has a higher coefficient of thermal expansion than steel, so the two metals grow at different rates when heated.
Example Sentence 2
Engineers account for the coefficient of thermal expansion when fitting turbine blades so clearances remain correct at operating temperatures.