Thermal Expansion:
When heat is applied to most materials, expansionoccurs in all directions.
Conversely, if heat energy is removed from a material (i.e. the material is cooled) contraction occurs in all directions. The effects of expansion and contraction
each depend on the change of temperature of the material.
Thermal expansion and contraction are very important features in engineering science. For example, if the metal railway lines of a railway track are heated
or cooled due to weather conditions or time of day, their lengths can increase or decrease accordingly. If the metal lines are heated due to the weather effects,
then the railway lines will attempt to expand, and depending on their construction, they can buckle,
rendering the track useless for transporting trains. In countries with large temperature variations, this effect can be much worse, and the engineer may have to choose a superior metal to withstand these changes.
The effect of metals expanding and contracting due to the rise and fall of temperatures, accordingly, can
also be put to good use. A classic example of this is the simple humble domestic thermostat, which when the
water gets too hot, will cause the metal thermostat to expand and switch off the electric heater; conversely,
when the water becomes too cool, the metal thermostat shrinks, causing the electric heater to switch on again. All sorts of materials, besides metals, are affected by
thermal expansion and contraction.
