Barometric Pressure Simple Explanation: Definition and Calculation Method. Learn how to use a barometer to determine atmospheric pressure.
A barometer is a scientific instrument used in meteorology to determine atmospheric pressure . Many measurements, however, are used within surface analysis to help find depressions, high pressure systems, and frontal boundaries.
Barometers and altimeters perform the same role, but are used for different purposes: an altimeter is meant to be carried from one place to another , while a barometer is kept stationary and measures subtle changes in pressure over time.
Perform a specific equation
Atmospheric pressure , when measured by a barometer , is called ” barometric pressure .” The barometer, typically a tube filled with mercury, measures the air pressure based on the column of mercury it raises . At the bottom of the barometer, the pressure is equal to atmospheric pressure, while at the top, the pressure is very low, with only mercury vapor present.
To calculate atmospheric pressure using a barometer, the equation is used: Pₐₜₘ = ρgh , where “ρ” is the density of mercury, “g” is the gravitational acceleration, and “h” is the height of the mercury column above the free surface.
It is important to note that the physical dimensions of the barometer, such as the length of the tube and the cross-section, do not affect the height of the mercury column. This means that regardless of the size of the tube, the atmospheric pressure will always be determined by the same relationship, provided that mercury is used as the fluid.
Knowing the density of mercury
In thermodynamic calculations, a commonly used unit of measurement is the standard atmosphere , defined as the pressure of a column of mercury 760 millimetres high at 0 °C. To determine the density of mercury, the formula is used: ρHg = 13.595 kg/m³ and the gravitational acceleration is taken as: g = 9.807 m/s² .
It is important to note that the density of mercury can vary with temperature ; therefore, it is essential to correct the reading before performing calculations. A thermometer should generally be mounted on the barometer to ensure that the measurements are accurate.
Furthermore, for aneroid barometers , commonly used in households, temperature compensation is achieved by inserting a bimetallic element into the mechanical connections. This measure ensures that pressure measurements are reliable, even in the presence of variations in ambient temperature.
Buying a digital barometer
In conclusion, once you have learned the equations to calculate barometric pressure, it is useful to compare it with atmospheric pressure to highlight the substantial differences.
Although both measurements serve a similar role, the main distinction is that atmospheric pressure, as the name suggests, refers only to the pressure exerted in the Earth’s atmosphere. In contrast, barometric pressure is that which is measured by the instrument called a barometer.
It is important to note that there are both analog and digital barometers on the market . Buying a digital barometer is often the best choice, as it allows for calculations with a very small margin of error, ensuring more precise and reliable measurements.
