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
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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.
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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.
FAQs on Atmospheric Pressure
1. What is atmospheric pressure?
Atmospheric pressure is the force exerted per unit area by the weight of the column of air above a specific location on the Earth's surface. This pressure is a result of Earth's gravity pulling the air molecules downwards. It is also known as barometric pressure and is a fundamental concept in physics and meteorology.
2. How is atmospheric pressure calculated or measured?
Atmospheric pressure is measured using an instrument called a barometer. The standard formula derived from a mercury barometer experiment is Pₐ = ρgh, where:
- Pₐ is the atmospheric pressure.
- ρ (rho) is the density of the fluid (e.g., mercury).
- g is the acceleration due to gravity.
- h is the height of the fluid column supported by the atmosphere.
3. What is the standard value of atmospheric pressure at mean sea level?
The standard atmospheric pressure at mean sea level, often denoted as 1 atmosphere (atm), is a constant used for scientific calculations. Its value in various common units is:
- 1 atm
- 101,325 Pascals (Pa) or 101.325 kilopascals (kPa)
- 760 mm of mercury (mmHg) or 76 cm of mercury
- 1.01325 bar
- Approximately 14.7 pounds per square inch (psi)
4. Why does atmospheric pressure decrease with an increase in altitude?
Atmospheric pressure decreases as altitude increases because there is less air above you. As you go higher, the column of air weighing down on a surface becomes shorter and less dense. With fewer air molecules exerting force, the overall pressure is lower. This is why mountaineers often need supplemental oxygen at high elevations and why it's harder to breathe on top of a tall mountain.
5. How does atmospheric pressure affect the boiling point of a liquid like water?
Atmospheric pressure has a direct impact on the boiling point of a liquid. For water to boil, its vapour pressure must equal the surrounding atmospheric pressure.
- At sea level (high pressure), water boils at 100°C.
- At higher altitudes (low pressure), water boils at a temperature below 100°C because less vapour pressure is needed to match the lower external pressure. This is why food takes longer to cook in the mountains.
6. What is the difference between atmospheric pressure and gauge pressure?
The key difference lies in their reference point. Atmospheric pressure is the absolute pressure exerted by the atmosphere. Gauge pressure, on the other hand, is the pressure measured relative to the local atmospheric pressure. For instance, a tyre pressure gauge measures the pressure inside the tyre *above* the surrounding atmospheric pressure. The relationship is: Absolute Pressure = Gauge Pressure + Atmospheric Pressure.
7. If atmospheric pressure is so high, why don't we feel its crushing force?
We don't feel the immense atmospheric pressure because the fluids inside our bodies (like blood) exert an equal and opposite pressure outwards. This internal pressure perfectly balances the external atmospheric pressure, creating a state of equilibrium. We only notice a change in pressure, such as when our ears 'pop' during a rapid change in altitude.
8. What are some real-world examples of atmospheric pressure in action?
Atmospheric pressure is at work all around us. Some important examples include:
- Drinking with a straw: When you suck on a straw, you reduce the pressure inside it, allowing the higher external atmospheric pressure to push the liquid up into your mouth.
- Barometers: These devices use the pressure of the atmosphere to predict weather changes.
- Syringes: Pulling the plunger back creates a vacuum, and atmospheric pressure forces the liquid into the barrel.
- Aircraft Altimeters: These instruments measure altitude by detecting the change in atmospheric pressure.
