Linear expansivity is a material's tendency to lengthen in response to an increase in temperature. Linear expansivity is a type of thermal expansion. It is described by a fraction that represents the fractional increase in length of a thin beam of a material exposed to a temperature increase of one degree Celsius. The fraction is called the linear expansion coefficient of the material.
Linear expansivity is one way to measure a material's thermal expansion response. The linear expansion coefficient is used by scientists to accurately predict a material's thermal expansion in area and volume when length is added. To predict a change in length, the original length is multiplied times the known linear expansion coefficient and the amount of the temperature increase in degrees Celsius.
Linear expansivity is used in many real world applications. Metal strips inside some thermometers lengthen in response to temperature increases. The thermometer's scale is created with the linear expansion coefficient in mind to accurately display the proper temperature.
Another practical application of linear expansivity is loosening a metal jar lid with hot water. When the lid is held under running hot water, the length of the part of the jar connected to the glass bottle expands. This makes it easier to twist the metal lid off the jar.