A Venturi tube is a device used to measure the flow rate of fluids. It consists of a tube that narrows in the middle, creating a change in pressure as the fluid flows through. According to the Bernoulli principle, as the fluid speeds up in the narrower section, its pressure decreases, allowing for flow measurement. These tubes are commonly used in various applications, including water supply systems and industrial processes. By measuring the pressure difference between the wider and narrower sections of the tube, engineers can calculate the flow rate, making Venturi tubes essential tools in fluid dynamics.