Measuring pressure

The pressure in fluids (liquids and gases) can be measured with a manometer.

A manometer is a U-shaped tube, open on both sides, which contains a liquid. One arm of the manometer is connected to the vessel containing the fluid whose pressure is to be measured. This produces a pressure difference that displaces the liquid inside the manometer. The difference in the height, h, between the liquid in the two arms gives the difference between the fluid pressure being measured and the external atmospheric pressure. This pressure difference can be calculated from the formula

pressure difference = rgh

(where r is the density of the liquid in the manometer).