[Physics Class Notes] on Atmospheric Pressure Pdf for Exam

Define Atmospheric Pressure

Students know that atmospheric pressure can be calculated at any point. Evangelista Torricelli had introduced a new device to figure out the atmospheric pressure by the use of the concept.

Do you know what is atmospheric pressure? The explanation is very simple to understand. The atmospheric pressure of the earth is 101, 325 Pa. The total force exerted upon a surface by the air that lies above the surface because of the gravity pulls of the earth is called atmospheric pressure.

You can also call the atmospheric pressure as barometric pressure. 

1 atmospheric pressure = Pa = ρgh

Atmospheric Pressure Definition: Proof Using the Experiment of Evangelista Torricelli

In this experiment, you should take a long glass tube with its one end closed. Then fill that glass tube with mercury. Try to invert the tube into a trough of mercury. This device has a specific name now called mercury barometer. 

From the above figure, you can notice that the left-over area above the mercury column is occupied with mercury vapour. The pressure of that free area is negligible so that we can take it as a vacuum. 

Here, the pressure that lies within the column must be equal to the atmospheric pressure. They have to be the same as they are at the same level. 

So, Formula for standard atmospheric pressure is, Pa = ρgh

Here, h = height of the mercury

ρ = Density of the fluid

Pa = normal atmospheric pressure

g = acceleration due to gravity

What is Barometric Pressure?

The above experiment has used mercury with a height of 76 cm inside a column. This is why scientists term the barometric pressure as mm or cm of mercury.

The upcoming figure can give you an idea about the measurement of the pressure differences. The apparatus is termed a tube manometer.

This above equipment contains a U-tube that comes with a suitable liquid.  This is a type of a specific oil that helps to measure small pressure differences. 

Also, the liquid of high-density is available inside that tube for measuring large pressure differences. 

One side of the tube is open to the atmosphere. You can clearly visualize the figure as given above. Also, the other end of the tube is linked to the system. It would help if you went for the measurement of this given system’s pressure. Due to the identical levels of the liquids, the pressure ‘P’ is equal to the pressure Q.

Here, we set up the process to identify the gauge pressure. The pressure level of the tube P-Pa is mentioned before as the atmospheric pressure. It has a specific formula which is proportional to the height of the mercury column.

P1 is the pressure that we need to measure in the above experiment. The setup can give the basic idea about the working principle for finding the right atmospheric pressure.

Atmospheric Pressure at Sea Level

PMSL is the abbreviation used for the name ‘atmospheric pressure at mean sea level’. In this atmospheric pressure, you can have the benefits of getting the weather reports on radio, television, and newspapers. 

The Internet is not also left behind. All of the above processes are available to measure atmospheric pressure. As per multiple tests, barometers that are set for domestic purposes only can match the local weather reports. 

With the help of those displays, you can perform the adjust for the pressure at sea level. However, you cannot alter the actual local atmospheric pressure.

Atmospheric pressure adjustment is necessary when the altimeter setting is available within aviation as a mandatory option.

Average sea-level pressure can be given as Pavg = 1013.25 mbar 

The same value for average sea-level pressure in Pascal is, Pavg = 101.325 kPa; 

In the unit of mercury Pavg = 29.921 in-Hg or 760.00 mmHg

Some of the important parameters that are associated with the sea-level atmospheric pressure are given below within the table:

How Do You Define Surface Pressure?

Surface pressure is another term that is derived from atmospheric pressure. This states about the pressure of certain points that exist at a location on Earth’s surface. That point may be from anywhere such as terrain and oceans. 

Surface pressure is directly proportional to the mass of air present at the current location. For numerical reasons, atmospheric models such as general circulation models (GCMs) usually predict the non-dimensional logarithm of surface pressure.

Such as Three terms are so close with this formula pressure (p), mass (m), and the acceleration due to gravity (g). So, the relation is P = F / A = (m*g) / A, where A is surface area.