Original: Thermometers are another application of thermal expansion â "most contain a liquid (usually mercury or alcohol) which is constrained to flow in only one direction (along the tube) due to changes in volume brought about by changes in temperature.
Simplified: Thermometers are an example of an application of thermal expansion â "they contain a liquid which is constrained to flow in only one direction (along the tube) due to changes in volume brought about by changes in temperature.