Have you ever watched a railroad track? Between two consecutive pieces of rail there is a space. Likewise, very long concrete bridges are not built in a single block. They are made up of several concrete blocks, built side by side. These spaces are left by builders because most materials expand with increasing temperature.
Therefore, when a material (or substance) is heated, its dimensions change. In most cases involving solids, these variations are easily noticed, but an observation rigorous is able to indicate factors that will influence the dilation process suffered by the substance.
As the expansion is caused by the increase in temperature, we can say that the greater the increase in temperature, the greater the expansion. Thus, for not very large variations in temperature, the length dilation is proportional to it, being normally imperceptible.
As for linear expansion, we can state that the type of material has an influence on the substance's expansion. This characteristic of materials can be represented by a number called the coefficient of expansion that is obtained experimentally and that informs how much a unit of length of the substance expands when it undergoes temperature variation of 1°C.
How each of these factors (temperature variation, initial bar length and material of the which it consists of) influences the expansion can be translated mathematically by a very simple. Let's see the figure above, in it we have a metallic bar of length L0 and initial temperature T0, at be heated for a certain period of time, it will have a final length L and a final temperature TO.
In this way, the bar undergoes a linear dilation ΔL that can be calculated by the difference between L and L0 when it suffered a variation in its temperature (ΔT) calculated between T and T0. So we have:
ΔL=L0 .α .ΔT or L=L0 (1+ α.ΔT)
In SI, the initial length of the bar is given in meters, the coefficient of linear expansion of the material α is given in K-1 and the temperature change ΔT is given in K. However, it is more usual to use the coefficient of expansion of the material in °C-1 and temperature variation in °C.
By Domitiano Marques
Graduated in Physics
Source: Brazil School - https://brasilescola.uol.com.br/fisica/dilatacao-linear-dos-solidos.htm
