sentences:  When a chemical reactor is being brought into operation, the concentrations, temperatures, species compositions, and reaction rates are changing with time until operation reaches its nominal process variables.When a switch is flipped in an appropriate electrical circuit containing a capacitor or inductor, the component draws out the resulting change in voltage or current (respectively), causing the system to take a substantial amount of time to reach a new steady state.We can define a transient by saying that when a quantity is at rest or in uniform motion and a change in time takes place , changing the existing state , a transient has taken place.