which is a Bernoulli equation valid also for unsteady—or time dependent—flows. Here denotes the partial derivative of the velocity potential with respect to time , and is the flow speed. The function depends only on time and not on position in the fluid. As a result, the Bernoulli equation at some moment does not only apply along a certain streamline, but in the whole fluid domain. This is also true for the special case of a steady irrotational flow, in which case and are constants so equation () can be applied in every point of the fluid domain.