In physics we can say that thermal expansion it is the increase in body dimensions from the increase in temperature. It occurs with almost all materials, in solid, liquid or gaseous state. We say that the dilation of the body is related to the thermal agitation of the molecules that make up the body, because we know that the hotter the body, the greater the thermal agitation of its molecules.
The more molecules in a body vibrate (shake), the more space they need to vibrate. Thus, the increase in body dimensions is due to the increase in the space between the molecules that make up the body. Therefore, if the increase in temperature produces thermal expansion of the body, a reduction in temperature will cause a decrease in volume, that is, it will cause contraction of the body.
In thermology studies, we take into account three types of thermal expansion: a linear dilation, which is linked to the increase in body length when it is warmed up; The surface dilation, which is linked to the increase in the length and width of the body, that is, there is an increase in two dimensions; and the
volumetric dilation, which is linked to the increase of the body in three dimensions, that is, with the increase in temperature, the body varies in length, width and height.It is often difficult to perceive with the naked eye (that is, without the use of instruments) the thermal dilation of bodies. In our daily life, we face several situations in which it is necessary to take into account thermal expansion, for example: the rails of the trains are placed so that there is always a small space between them, to avoid deformations (figure above) when they heat up; on cemented sidewalks are placed expansion joints between the cement slabs to avoid deformations due to temperature increase, etc.
Like solids, liquids also swell with increasing temperature. Although liquids do not have their own shape (they take the form of the containers that contain them), we have not defined for them the linear and surface expansion coefficients, we define only the expansion coefficient volumetric.
So, for us to study the volumetric expansion of liquids, it is necessary that they are contained in a container, which by the way will also expand. So we generally need to take into account two dilations, the liquid dilation and the container dilation.
By Domitiano Marques
Graduated in Physics
Brazil School Team
Source: Brazil School - https://brasilescola.uol.com.br/fisica/dilatacao-termica.htm