Atmospheric pressure

Содержание и основные понятия

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Alterna · physics · 3.3
Atmospheric pressure
Torricelli experience, barometer, gauges, press
The air weighs, and it pressures us with a force of 1 kg per square inch, like Torricelli measured the atmosphere with mercury and how barometers work.
GEF · Grade 7
PIF · Baseline
01
Atmospheric pressure
The air has its weight, and it's pressing us.
Air weight
Air is a mixture of gases (azoth, oxygen, argon, etc.). Like any substance, air has
Mass
And so does the weight.
At sea level, atmospheric pressure — near
101325 Pa (760 mm Art.)
.
Every square inch of the Earth's surface is pressed by an air column of about 1 kg!
It's curious: the history of discovery
In 1643
Evangeist Torricelli.
The first time he measured atmospheric pressure, he filled the glass tube with mercury, turned it into a bowl of mercury, the pole dropped to 760 mm.
Torricelli experience
.
02
Torricelli's experience
How was atmospheric pressure measured?
Torricelli's experience
A glass tube with a length of ~1 m is filled with mercury, turned into a bowl with mercury; the mercury column is lowered to a height of ~760 mm above it.
vacuum (empty tortilla)
.
The atmospheric pressure shall be balanced by the pressure of the mercury column:
p
Atm.
= ρ
pht
· g h = 13600 · 9.8 · 0.66 ~ 101325 Pa
🍇
Torricelli's experience
IV-026 · Slider height + slope of tube
Height:
0
km
03
Antheroid barometer
Instrument for measuring atmospheric pressure without liquid.
Antheroid barometer
Antheroid barometer
- Atmospheric pressure measuring device with no liquid.
metal box
When the pressure changes the box compresses or expands to pass the direction to the arrow.
Scale in mm mercury or gPa.
🎉
Barometer — Height and Pressure
IV-027 P(h): pressure drops with height
Height:
0
km
04
Manometers and pumps
Pressure measuring instruments for liquids and gases.
Manometer
Manometer
— A liquid or gas pressure measuring device (more or less than atmospheric pressure).
The liquid pressure gauge is a U-shaped fluid tube, and the different levels show the differential pressure.
Pumping liquid pump
Piston pump operation:
Push rises under valve, causing dilution
Atmospheric pressure is pressured by the lower valve in the well
Water rises into the pump
Thread drops down the lower valve closes, the top opens
The water rises at atmospheric pressure, not higher than ~10.3 m.
05
Hydraulic press
Winning power at the expense of different pistons.
Hydraulic press
Pascal's law gives you the same pressure:
F₁/S₁ = F₂/S₂   →   F₂ = F₁ · S₂/S₁
Winning is equal to S2/S1. But losing at a distance: a small piston goes a long way, a large one goes a small one.
🔨
Hydraulic Presses — Winners
IV-028 · Interactive press
F₁:
20
H
S₂/S₁:
10
x
C
What needs to be understood
Outcome 1
Explain the physical meaning of the topic "Atmosphere pressure" through the model, not just the formula.
Outcome 2
Distinguish and correctly use terms: atmospheric pressure, barometer, gauge.
Outcome 3
Indicate the conditions for the applicability of the law, verify units and limit cases.
T
Terms of the topic
The definition should indicate the physical meaning, not a substitute for a domestic synonym.
atmospheric pressure
The pressure generated by the atmosphere on the bodies and surfaces in it.
barometer
Atmospheric pressure measuring device.
pressure gauge
A liquid or gas pressure measuring device, often relative to atmospheric pressure.
Torricelli experience
A mercury pole experience that demonstrates atmospheric pressure and allows it to be measured.
F
Origin and conclusion of the formulas
The fundamental law cannot be "proven" by algebras: for each record, it is stated whether it is a definition, an experimental law, or a model effect.
p
=
ρ
g
h
p=\rho gh
p
=
ρ
g
h
model effect
Mercury pole pressure.
The following is an indication of the definition, experience or law from which this entry arises and where it is applicable.
p
верх
≈
0
p_{\text{верх}}\approx0
p
top
​
≈
0
Torricelli's experience with the mercury pole creates almost a vacuum.
p
атм
=
p
столба
p_{\text{атм}}=p_{\text{столба}}
p
Atm.
​
=
p
Pole
​
At one horizontal level, atmospheric pressure balances the mercury pole pressure.
p
атм
=
ρ
H
g
g
h
p_{\text{атм}}=\rho_{\mathrm{Hg}}gh
p
Atm.
​
=
ρ
Hg
​
g
h
The hydrostatic model links the measured height of the pole to atmospheric pressure.
Conditions:
Mercury is resting, density and g are known, vapour pressure above the pole is negligible; altitude is measured vertically.
Monitoring:
The dimensions of both parts shall coincide; the result shall be checked for sign, order and limit case.
!
Model boundaries and typical errors
Error: Forget model condition
You can't put the formula on any situation just because it's a coincidence of letters. The key condition of this subject is that air weighs, and it pressures us with a force of 1 kg per square centimeter. How Torricelli measured the atmosphere with mercury and how barometers work.
How to Check the Mind
The formula is only applicable after selecting the system and assumptions. Then check the unit, vector direction and result behaviour at zero or very large parameter.
Σ
Conclusion on the topic
Atmospheric pressure
The air weighs, and it pressures us with a force of 1 kg per square inch, like Torricelli measured the atmosphere with mercury and how barometers work.
The air weighs, and it pressures us with a force of 1 kg per square inch, like Torricelli measured the atmosphere with mercury and how barometers work.
The formula is applicable only after the selection of the system and assumptions.
Any numerical result shall be accompanied by a unit, a sign and an explanation of its physical meaning.
The content is consistent with the FRP on Physics of the OS/OSS 2025 and the subject matter of the current lines of the PNP: I. M. Peryškin and co-authors (7–9), G. J. Mäkishev and coauthors (10–11), and with the lines "Engineers of the Future" and V. A. Kasyanov. The original texts are not reproduced, the text of the textbooks is not reproduced.