A rotameter is a type of flow meter used to measure the flow rate of liquids or gases in a vertical pipe. It consists of a tapered transparent tube and a floating element (float) inside it. As the fluid flows upward through the tube, the float rises until the upward force of the fluid equals the weight of the float. The position of the float indicates the flow rate, which can be read on a calibrated scale on the tube. Rotameters are simple, reliable, and require no external power, making them widely used in laboratories, water treatment systems, chemical industries, and gas flow measurement applications.