Thermal energy is the form of energy that any body has that has a temperature above absolute zero. Macroscopically, thermal energy is a large amount, and the amount of this energy a body possesses is proportional to temperature.
According to the second principle of thermodynamics, it is considered a form of degraded energy because not all thermal energy can be converted into mechanical energy. On the contrary, any other form of energy has the possibility of converting more or less spontaneously into thermal energy (such as mechanical energy by friction, electromagnetic energy by radiation absorption or electrical energy by resistive dissipation).
What does heat energy consist of?
Heat energy is the sum of the kinetic energy and the potential energy of all the atoms that make up a body. Kinetic energy is the energy associated with the oscillations or movement of molecules in the body. Potential energy is defined by its position within the body.
The average kinetic energy of all the molecules taken alone constitutes the thermal energy. At the microscopic level, the average kinetic energy of the molecules in the system takes into account the movements of translation, rotation and vibration of the molecules. Temperature increases with increasing average kinetic energy.
All substances are made up of molecules. These molecules are linked together by intramolecular forces of greater or lesser intensity. In solids, the 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 that their structure is non-deformable: in fact, all solids have their own shape and volume.
The oscillation of the molecules is of more or less great 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 substances increases with increasing temperature: at higher temperatures correspond greater oscillations of amplitude than the molecules (or atoms) for which the charges responsible for electrical conduction find it more difficult to cross the material.
In liquids, molecules are held together by weaker forces, and for this reason, a liquid does not have its own shape.
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.
How is heat energy produced?
Heat energy can be produced in large quantities through reactions such as:
- Chemical combustion reactions
- Nuclear reactions
- Through the passage of electricity through a cable characterized by a defined resistance greater than 0 given by the composition of the material it conducts (that is, by the Joule effect), as occurs in electric heaters and all devices that heat the medium environment (washing machine, electric oven, etc.).
- Through natural sources of heat energy: the Sun and the subsoil.