Barometric Pressure vs Atmospheric Pressure
Atmosphere pressure and barometric pressure are two important concepts in pressure and thermodynamics. It is vital to have a clear understanding in these concepts in order to excel in such fields. This article will discuss what pressure, atmospheric pressure and barometric pressure are, their similarities, definitions and differences between atmospheric pressure and barometric pressure.
What is Atmospheric Pressure?
An understanding of the concept of pressure is required to understand atmospheric pressure. Pressure is defined as the force per unit area applied in a direction perpendicular to the object. The pressure of a static fluid is equal to the weight of the fluid column above the point the pressure is measured. Therefore, the pressure of a static (non-flowing) fluid is dependent only of the density of the fluid, the gravitational acceleration, the atmospheric pressure and the height of the liquid above the point the pressure is measured. The pressure can also be defined as the force exerted by the collisions of particles. In this sense, the pressure can be calculated using the molecular kinetic theory of gasses and the gas equation. Atmospheric pressure is defined as the force per unit area exerted against a surface by the weight of air above that surface in the Earth’s atmosphere. When going to the high altitudes, the air mass above the point decreases, thereby reducing the atmospheric pressure. The atmospheric pressure at the mean sea level is taken as the standard atmospheric pressure. The pressure is measured in Pascal (unit P). This unit is also equivalent to Newton per square meter. Other widely used units are the Hgmm or Hgcm, which means the equivalent mass of the mercury column the air pressure can support. The atmospheric pressure at the mean sea level is taken as 101.325 kPa or sometimes as 100 kPa.
What is Barometric Pressure?
A barometer is a device, which consists of a glass tube that is closed at one end and filled with a high density liquid and vacuum between the top of the liquid and the tube, and the other end of the tube is submerged in an open container containing the same liquid. When mercury is used as the liquid this apparatus is termed as mercury barometer. Since the pressure of the vacuum is zero and the pressure at the liquid surface is P, the pressure difference is also P. This pressure difference is responsible for holding the liquid column. Therefore, the force from the pressure difference is equal to the weight of the column. Cancelling out the area on both sides, we get P = hdg, where h is the height of the column, d is the density and g is the gravitational acceleration. The pressure that is measured using the barometer is the barometric pressure. This is equal to the atmospheric pressure, if the open end is in the atmosphere.
What is the difference between Atmospheric Pressure and Barometric Pressure?
• Atmospheric pressure at the mean sea level is a constant defined.
• Barometric pressure is the pressure measured using the barometer.