Knowra State variable State variable A state variable is a measurable property whose value helps specify the state of a physical system. Examples include pressure, temperature, volume, and energy.
Thermodynamic state : A macroscopic condition of a system specified by properties such as pressure, temperature, and composition. State variables provide coordinates for describing this condition.
State function : A quantity whose value depends only on a system's state, not on the process used to reach it. State variables are commonly treated as coordinates or values of state functions.
Ideal gas law : The equation relating pressure, volume, temperature, and amount of an ideal gas. It links several measurable state variables in a simple system.
State variable (control theory) : A variable in a dynamical model whose value, together with inputs, determines the system's future behavior. This engineering meaning concerns dynamical models rather than measurable thermodynamic properties.
Thermodynamic equilibrium : A condition in which a system's macroscopic properties remain constant and no net flows or changes occur. State variables have stable, well-defined values at equilibrium.
Path function : A quantity whose value depends on the process followed between two states. Heat and work depend on the path, unlike state-variable changes.
Internal energy : The total microscopic kinetic and potential energy contained within a physical system. It is a state variable that can be related to temperature and volume.
State vector : A vector that collects the variables needed to describe a system's state. A state vector groups state variables into one mathematical description.
Equation of state : A relation among state variables that describes allowed states of a physical system. It constrains which combinations of state-variable values are possible.
Thermodynamic cycle : A sequence of thermodynamic processes that returns a system to its initial state. State variables return to their starting values after a complete cycle.
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