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Thermal energy

Thermal energy

Thermal energy is the form of energy possessed by any body that has a temperature above absolute zero. Macroscopically, thermal energy is an extensive amount and the amount of this energy that a body possesses is proportional to the temperature.

According to the second principle of thermodynamics, it is considered a degraded form of energy because not all thermal energy can be converted into mechanical energy. By contrast, any other form of energy has the potential to become more or less spontaneously thermal energy (such as mechanical energy by friction, electromagnetic energy by absorption of radiation or electrical energy by resistive dissipation).

Microscopic interpretation of thermal energy

The sum of the kinetic energy associated with the oscillations or the movement of the molecules that constitute a body and the potential energy due to their mutual position constitutes the internal energy. The average kinetic energy E c of all the molecules taken alone constitutes the thermal energy. At the microscopic level, the average kinetic energy E c of the molecules of the system takes into account the movements of translation, rotation and vibration of the molecules. The temperature increases with the increase of the average kinetic energy.

All substances are composed of molecules. These molecules are linked together by intramolecular forces of greater or lesser intensity. In solids, molecules are not immobile in space, but oscillate around their equilibrium position. Therefore, they are in constant turmoil. However, strong enough ties hold them together, so their structure is indeformable: in fact, all solids have their own shape and volume.

The oscillation of the molecules is of more or less large amplitude depending on the amount of thermal energy that a body possesses. For high temperatures, the oscillations are wider, while at lower temperatures they correspond to smaller oscillations. This fact explains how the electrical resistance of the substances increases when the temperature increases: at higher temperatures amplitude oscillations are greater than the molecules (or atoms) for which the loads responsible for electrical conduction find it more difficult to cross the material.

In liquids, molecules are linked by weaker forces and, for this reason, a liquid does not have its own form.

In the gas of molecules they enjoy extreme freedom of movement. They move in a very chaotic and informal way as the gas temperature increases.

Production of thermal energy

Thermal energy can be produced in large quantities simply through chemical reactions of combustion, or through nuclear reactions, or even through the passage of electrical current through a cable characterized by a defined resistance and greater than 0 given by the composition of the material that it conducts (that is to say, by Joule effect), as it happens in the electric heaters and all the devices that heat the environment (washing machine, electric oven, etc.). There are two natural sources of thermal energy: the Sun and the subsoil.

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Last review: October 2, 2018

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