Thermodynamics is a branch of physics which studies the laws that govern the conversion of energy from one form to another. It studies the direction in which the energy flows and the availability of energy to do work.
It is based on the assumption that in an isolated system there is a measurable amount of energy called internal energy which is usually denoted by letter U. This is the total energy of this isolated system and it is a sum of kinetic and potential energy of the atoms and molecules of the system of all kinds. It can be transferred directly as heat to other systems if we “connect” these systems. This definition of internal energy U excludes nuclear and chemical energy. The value of U can be changed only if we “remove” the isolation of the system by connecting it to other one. In such a case we can change the internal energy by transferring among the system:
mass, heat, or work being done on or by the system.
As in other chapters of this physics tutorial the next paragraphs will be devoted to different subjects that belong to branch of thermodynamics.
At the end of each paragraph a number of problems with solutions will be presented as solving problems is the best way to learn physics. It is the best help in understanding physics.