Which instrument measures pressure by utilizing a U-shaped tube partially filled with fluid?

The instrument that measures pressure using a U-shaped tube partially filled with fluid is the manometer. A manometer operates on the principle of balancing the pressure of the fluid in the tube against the atmospheric pressure or another pressure source. By observing the height difference of the fluid in the two arms of the U-tube, one can calculate the pressure exerted by the fluid being measured. This method is especially useful for measuring small pressures, such as in laboratories or HVAC systems, and is a fundamental principle in fluid mechanics.

While other instruments listed have their specific functions—like hydrometers measuring fluid density, barometers measuring atmospheric pressure, and vacuum gauges measuring pressures below atmospheric levels—the manometer’s unique U-shaped design and fluid column offer a direct and straightforward means of pressure measurement.