What is state variable?

State variable is a characteristic or property of a system that determines its behavior over time. It is a measurable property of a physical system, which can be described by a set of numerical values. State variables are commonly used to describe the state of a physical system in mathematical models or simulations.

Examples of state variables include temperature, pressure, volume, mass, energy, and density. For instance, in a gas system, temperature, pressure, and volume are considered as state variables that depend on each other.

Changes in state variables can result in a change in the system's behavior, such as a change in temperature leading to a change in the system's physical state. These variables are often used to determine the equilibrium state of a system, which is achieved when all of the state variables remain constant over time.

State variables are essential in the field of physics, engineering, and other scientific disciplines to describe the behavior of physical systems. They are also important in the development of control theory, which aims to manipulate state variables to regulate and stabilize a system.