THERMAL EXPANSION
When a substance undergoes a temperature change, it changes in size. Steel beams
that form railroad tracks expand when they get warmer; a balloon filled with air
shrinks when it’s placed in a freezer. The change in size of a substance due to a
temperature change depends on the amount of the temperature change and the
identity of the substance.
Let’s first talk about changes in length (of the steel beam, for example). When its
temperature is T 0 , its length is L 0. Then, if its temperature changes to Tf, the length
changes to Lf, such that
Lf − L 0 = α Li(Tf − T 0 )where α is the coefficient of linear expansion of the material. This equation is
usually used in the simpler form
∆L = αL 0 ∆TNearly all substances have a positive value of α, which means that they expand
upon heating.
- A steel beam used in the construction of a bridge has a length of
30.0 m when the temperature is 15°C. On a very hot day, when the
temperature is 35°C, how long will the beam be? (The coefficient of
linear expansion for structural steel is +1.2 × 10−5/C.)
Here’s How to Crack It
The change in length of the beam is
As we’ve mentioned, substances also undergo volume changes when heat is lost or