Non-equilibrium thermodynamics is a branch of thermodynamics that deals with physical systems that are not in thermodynamic equilibrium. A fundamental difference separates equilibrium from non-equilibrium thermodynamics in that the former deals primarily with closed systems as moving from one state of equilibrium to another – such as the heating and cooling of a material – while the latter deals primally with open systems that are in constant flux and change – such as an ecosystem. Most natural and engineered systems are not in thermodynamic equilibrium. They are changing or can be triggered to change over time, and are continuously subject to flux of matter and energy to and from other systems. Equilibrium thermodynamics restricts its considerations to processes that have initial and final states of thermodynamic equilibrium; the timecourses of processes are deliberately ignored. But with Far from equilibrium systems, the forward and reverse reaction rates no longer balance and the concentration of reactants and products is no longer constant. Damping of acoustic perturbations or shock waves are nonstationary, nonequilibrium processes, driven complex fluids, turbulent systems and glasses are other examples of non-equilibrium systems within physics.