The expansion of bodies when heated and compress when cooled in the nature play a huge role. Uneven heating of air at the Earth's surface creates convection currents (the wind), contributing to the change in the weather. Uneven heating of the water in the seas and oceans creates currents, influence the climate of coastal countries. Particularly sharp temperature fluctuations occur in mountainous areas. This leads to alternating expansion and contraction of rocks. Because such volume changes will depend on the nature of the substance, it is in rocks, the more complex the, there are cracks, gradually increase, t. e. is the destruction of these rocks.In everyday life and technology dependence of the density of the substance, the length and volume of solids with temperature is also very important. The dependence of air density on temperature is used in apartments for even heat distribution, emitted by furnaces and radiators, in furnaces for producing thrust, in the refrigerator — for uniform cooling of the camera and t. d.

In various automatic devices are used bimetallic strip. This plate consists of two dissimilar metal strips, riveted with each other. When heated bimetallic strip one strip elongates more than the other, and the whole plate is bent (rice. 13.4, and); the contact on the bimetallic plates (rice. 13.4, b) when heated opens. These plates are used for automatic actuation and de-actuation of electrical circuits in the thermostats, in refrigerators, in fire-fighting devices and t. p.

The length dependence on temperature has to be considered when stringing the wires on the power lines, device steam, construction of bridges, the laying of rails and t. d.

To obtain junctions of metal with glass, for example, in the manufacture of electric lamps and radio tubes, used metals and glass with similar coefficients of expansion.