The science of thermal phenomena is thermodynamics. Physics considers it as one of its sections, which allows us to draw certain conclusions based on the representation of matter in the form of a molecular system.
Thermodynamics, the definitions of which are based on the foundation of facts obtained experimentally, do not use the accumulated knowledge about the internal structure of matter. However, in some cases, this science uses molecular kinetic models to clearly illustrate its conclusions.
The pillar of thermodynamics is the general laws of processes that occur when thermal energy changes , as well as the properties of a macroscopic system, which is considered in a state of balance. The most significant phenomenon occurring in the complex of substances is the alignment of the temperature characteristics of all its parts.
The most important thermodynamic concept is the internal energy that any body possesses. It is enclosed in the element itself. The molecular-kinetic interpretation of internal energy is a quantity representing the sum of the kinetic activity of molecules and atoms, as well as the potential of their interaction with each other. From here follows the law discovered by Joule. His confirmation was multiple experiments. They substantiated the fact that, in particular, an ideal gas has internal energy, consisting of the kinetic activity of all its particles, which are in a chaotic and random movement under the influence of heat.
Work in thermodynamics changes the activity of the body. The impact of forces affecting the internal energy of the system can have both positive and negative values. In those cases when, for example, a gaseous substance undergoes a compression process that is carried out in a cylindrical container under the pressure of a piston, the forces acting on it do some kind of work, characterized by a positive value. Opposite phenomena occur simultaneously. Gas performs negative work of the same magnitude on the piston acting on it. The actions performed by the substance are directly dependent on the area of the existing piston, its movement, as well as the pressure of the body. The work in thermodynamics that is performed by gas is positive when it expands, and when compressed, it is negative. The magnitude of this action is directly dependent on the path along which the transition of the substance from the initial position to the final one was completed.
The work in the thermodynamics of solids and liquids differs in that they change the volume very slightly. In connection with this influence of forces is often neglected. However, the result of a work substance can be a change in its internal activity. For example, when drilling metal parts, their temperature rises. This fact is evidence of the growth of internal energy. Moreover, this process is irreversible, since it is impossible to carry out in the opposite direction.
Work in thermodynamics refers to its main physical quantities. Its measurement is made in Joules. The value of this indicator is directly dependent on the way in which the system passes from the initial state to the final one. This action does not apply to body state functions. It is a function of the process itself.
Work in thermodynamics, the determination of which is carried out according to the available formulas, is the difference between the amount of heat supplied and removed in a closed cycle period. The value of this indicator depends on the type of process. If the system gives its energy, then this means that a more positive action is performed, and if it receives, a negative one.