Conductivity is a property of conductive elements. This is the name given to those materials that have the ability to transmit electricity or heat .
When a material allows electricity to pass through itself it is said to have electrical conductivity . On the other hand, if it allows heat to pass through, it is called thermal conductivity .
It can be indicated, therefore, that thermal conductivity is the property of those elements that enable heat transmission. This physical property implies that, when a matter has thermal conductivity, heat passes from the body with a higher temperature to another with a lower temperature that is in contact with it.
This heat transfer involves an exchange of internal energy (which combines potential energy and kinetic energy ) of electrons, atoms and molecules. The higher thermal conductivity, the better heat conduction. The inverse property is thermal resistivity , which indicates that the lower the thermal conductivity, the more heat insulation (more resistivity).
With respect to potential energy , we can say that it is the mechanical energy that is associated with the location of a body in a field of forces (in this case we are talking about electrostatic or gravitational energy , among others) or with the presence of a field of forces within the body itself (in such a case, the energy would be elastic ). In other words, potential energy is the result of the system of forces that affects a given body being conservative , that is, its total work on a particle is zero.
The kinetic energy of a body, for its part, is what it has thanks to its movement . This is the work needed to achieve its acceleration from rest to a given speed. When the body achieves this energy during acceleration, it maintains it unless it alters its speed. To return to the state of rest, it is necessary to do negative work with the same magnitude.
By heating matter, the average kinetic energy of its molecules increases, and this causes their level of agitation to increase. At the molecular level, heat conduction occurs because molecules interact with each other, exchanging kinetic energy without performing global movements of matter . It is worth mentioning that at a macroscopic level it is possible to model this phenomenon using Fourier's law .
Fourier's law states that thermal conductivity leads to a proportional flow by heat transfer conduction (the process by which heat spreads in different media), in an isotropic medium (a space in which the physical properties are not tied to the direction in which they are examined), which is proportional and opposite to the temperature gradient in that direction.
The formula for Fourier's law states that the heat flow across a given surface, measured with a given unit, is equal to the thermal conductivity times the temperature gradient within the material, all multiplied by -1 .
Metals are good thermal conductors : that is why they are used in those industrial procedures where the aim is to maximize heat transmission. Other materials, such as fiberglass, have such low thermal conductivity that they are used as insulators.
The heat conduction capacity is indicated through a magnitude known as the thermal conductivity coefficient . This coefficient, in the International System of Units, is expressed in watts / (meter x kelvin) . It can also be expressed in BTU / (hour x foot x Fahrenheit) in the Anglo-Saxon system and in kilocalories / (hour x meter x kelvin) in the technical system.