Heat and temperature _______________________________________________________________________________________________________________________________________________________________________________________________________________________ 9. Thermal expansion
Figure 7.6 Expansion joint in roadThe expansion of alcohol in a thermometer is one of many commonly encountered examples of thermal expansion, the change in size or volume of a given mass with temperature.
Hot air rises because its volume increases, which causes the hot air’s density to be smaller than the density of surrounding air, causing a buoyant (upward) force on the hot air.
The same happens in all liquids and gases, driving natural heat transfer upwards in homes, oceans, and weather systems.
Solids also undergo thermal expansion.
Railroad tracks and bridges, for example, have expansion joints to allow them to freely expand and contract with temperature changes.
As we have seen in Kinetic Theory of matter, an increase in temperature implies an increase in the kinetic energy of the individual atoms and particles, and, therefore, they move faster.
As a consequence, the distances between the particles gets bigger, and they take up more space. The result is that the body increases its volume, it expands.