Fluids
Fluids are substances composed of a collection of molecules that are arranged in a random manner, resulting in weak intermolecular forces. A key characteristic of fluids is their ability to respond readily to external forces exerted on them from the walls of their container or from outside sources. As such, fluids do not possess a defined shape. Common examples of fluids include air, water, and blood. Their significance in the field of physics is substantial due to their essential roles in various applications, such as shipbuilding, dam construction, submarines, pumps, and pressure measurement instruments. This article will explore the devices used for measuring fluid pressure.
Fluid Pressure Measurement Devices
Fluid pressure refers to the force exerted by a fluid vertically across a surface from all directions, essentially indicating the amount of force acting per unit area. This includes the force applied against the walls of the container holding the fluid. It is important to mention that pressure is measured in pascals (Pa), named after the renowned French scientist Blaise Pascal. There are two primary types of fluid pressure measurement devices, which are utilized for measuring atmospheric pressure, and they are classified as follows:
Mercury Barometer
The mercury barometer is an instrument featuring a long glass tube that is open at one end and filled with mercury. When the device is placed at sea level, the mercury within the tube drops to a height of 76 cm due to the high density of mercury, leaving a small vacuum at the top due to the presence of mercury vapor. This device is noted for its accuracy, as the cohesive forces between mercury molecules are greater than the adhesive forces between the mercury and the glass. Its distinctive color facilitates easy visibility. The pressure value indicated by this barometer is dependent on the altitude relative to sea level.
Metallic Barometer
The metallic barometer consists of a flexible, sealed metal box containing air at a low pressure. The design allows for the sides to be compressed inward as pressure increases, causing an indicator to move and reflect the pressure value. This device is commonly used for measuring fluid pressure and is preferred over the mercury barometer due to the challenges associated with handling liquid mercury. The metallic barometer’s design allows for easy portability and use; however, it is not as precise as the mercury barometer. Calibration of the metallic barometer is typically done using the mercury barometer for accuracy.