The Venturi effect is a physical phenomenon that goes back to the Italian physicist Giovanni Battista Venturi. It describes the increase in speed and decrease in pressure in a flow channel when the flow passes through a constriction. The effect occurs when a fluid (such as air or water) moves through a constricted passage, for example through a nozzle or a narrow point in a pipe. At the narrow point, the flow velocity of the fluid increases as it has to flow through a narrower space. However, according to Bernoulli's principle, the pressure of the fluid decreases as its velocity increases. This means that in a section with a narrower cross-section, the velocity of the flow increases while the pressure decreases. When the fluid then leaves the narrower section and re-enters a wider space, it returns to its original velocity and pressure. Source: Two hundred and fifty things architects should know, Michael Sorkin