If a physical process is carried out in such a way that it can only be viewed as a sequence of states of equilibrium , this process is called quasi-static or quasi-stationary . The time scale on which a quasi-static process takes place must therefore be much slower than the period in which an equilibrium is established (the relaxation time ):
For this reason, quasi-static processes are sometimes also referred to as “infinitely slow”, which, however, gives the wrong impression that they are completely impractical or that they would take forever.
Although a respective state of equilibrium largely prevails at each point in time of the process, one goal of the process or the attempt is generally nevertheless to obtain different states or a characteristic curve . I.e. the equilibrium state at time t 1 can differ considerably from the equilibrium state at time t 2 . It should only be excluded that dynamic processes such. B. (shock) waves, have a significant influence on the results.