Abstract
One of the oldest problems in the history of hydraulics is the outflow from a vessel through an orifice. In 1644, it was described by the Torricelli principle stating that the outflow velocity is the fall velocity from the filling level. From a theoretical point of view, the Torricelli principle is valid because it follows from Bernoulli's energy conservation principle. In this paper, the outflow problem will be described by Newton's momentum balance principle. Here, the Torricelli formula is obtained when the rounded orifice is treated as a contraction. For the sharp-edged orifice the bulk outflow velocity is the fall velocity from half the filling height. In this momentum balance theory, no artificial outflow coefficients are needed to distinguish between the cases of sharp-edged and rounded orifices.
