Thermal Expansion: Linear, Volumetric, and Constrained Effects

All flashcards

What is thermal expansion?

A change in the size or volume of a system caused by a change in temperature, usually an increase when heated.

Why do solids generally expand when heated?

Heating increases particles’ kinetic energy. Because neighboring particles resist being pushed together more strongly than being pulled apart, their average separation increases.

What does the coefficient of linear expansion describe?

The fractional change in a material’s length per degree of temperature change. It is represented by $\alpha$.

What is the linear expansion equation?

For a small temperature change, $\Delta L=\alpha L_0\Delta T$, where $L_0$ is original length and $\Delta T$ is the temperature change.

How does a bimetallic strip work?

Two bonded metals expand by different amounts when heated because they have different $\alpha$ values. This makes the strip bend, allowing it to move a pointer or switch.

Quiz questions

1. When does thermal stress develop in an object?Answer: When a constraint prevents a temperature-driven expansion or contraction.
2. For a fully constrained elastic object, what gives the magnitude of thermal stress?Answer: $\sigma=Y\alpha|\Delta T|$
3. A rod is heated while both ends are fixed, preventing it from expanding. What type of stress develops?Answer: Compressive stress
4. At approximately what temperature is liquid water densest?Answer: $4\ {}^\circ\mathrm{C}$
5. A full container and its liquid warm together. Which expression estimates the liquid that spills when the liquid expands more than the container?Answer: $V_{\text{spill}}=(\beta_{\text{liquid}}-\beta_{\text{container}})V\Delta T$