8.1- Physics of the Atmosphere Flashcards
What is air?
The mixed air that makes up the atmosphere.
What does the air comprimise?
21% oxygen
78% nitrogen
1% other gasses
What are the “other” gasses in our air?
Argon, carbon dioxide and more.
What happens to the composition of air as altitude increases?
It stays relatively the same, however pressure decreases.
What is the pressure level of each part of the mixture is proportional to? (air)
Its mass contribution.
If the local pressure is 1 atmosphere (1 ATM) then how many atmospheres of oxygen are there?
0.2
At what altitude does the composition of air start to change?
60,000 feet
What is the average height of the atmosphere?
760km
What does the exosphere extend to?
10,000km
What 5 parts is the atmosphere divided into?
Troposphere
Stratosphere
Mesosphere
Thermosphere
Exosphere
(TSMTE)
What is the densest layer of the atmosphere?
Troposphere
How far does the Troposphere extend?
8-14.5 km
What aircraft fly in the troposphere?
Light aircraft and turboprops
What occurs in the troposphere as a consequence of solar heating?
Vertical air movement
What is the tropopause?
Thermodynamic gradient-stratification layer that marks the end of the troposphere.
Where does the tropopause lie above the equator?
Approx 17km
Why do jet airliners generally cruise in the tropopause?
Air is thinner resulting in less drag.
What is the tropopause also known as?
The isothermal layer because the temp is constant.
What height does the stratosphere extend too?
50km
What does the stratosphere include?
Ozone layer
In the stratosphere does the temp vary?
No
What temp is the stratosphere?
-56.5c
What are they key factors of the atmosphere that effect aircraft flight?
Pressure
Temperature
Density
Humidity
What is relative humidity referred too as?
Dimensionless ratio
What is a pascal equal too?
N/m squared
What does the ICAO deem the pressure at sea level?
1013 hPa (14.7psi)
What is the second method of calculation for static pressure?
pxgxh
p= atmospheric density
g= gravitational field strength
h= height of the atmosphere
What do barometers measure?
Absolute pressure
Barometers are not practical on aircraft so what is used instead?
Aneroid capsules
What is temperature a measure of?
Average kinetic energy of molecules.
What is the absolute zero degrees c in kelvin?
273.15
In aviation what is actual atmospheric temperature expressed as?
Outside Air Temperature
At 36,000ft what does the air temp stabilise at?
-56.5 degrees c
What is the equation for density?
p=m/v
As altitude increases, pressure and density…..?
Decrease
What are density and pressure directly proportional too and inversely proportional too?
Directly proportional too each other and inversely proportional to height.
Assuming fluids are allowed to expand freely, density decreases as what increases?
Temperature
What makes air density vary?
Relative humidity and temp
What is relative humidity?
Amount of water vapour present in the air compared to the max amount of water vapour the air can hold.
What is the relative humidity at 40,000ft?
1 or 2%
Density decreases as humidity….?
Increases
Humidity is greatly affected by…?
Temp
Pressure, temp and humidity all affect…?
Air density
Where does dynamic pressure act?
Direction of airflow.
What is dynamic pressure denoted by?
q
How is dynamic pressure worked out?
half p x v squared
p is fluid density
What is 1 bar equal too?
100,000 pascals
What is the standard atmosphere by ICAO known as?
International standard atmosphere (ISA)
What is the ISA sea level value of pressure?
1013.25 hPa
What is the ISA sea level value of density?
1.225kg/m3
What is the ISA sea level value of temp?
288.15K or 15 degrees c
What is the standard altitude for tropopause?
11km (36,000ft)
How much does the temp decrease per km in the troposphere?
6.5 degrees c per km.
In the stratosphere does the temp stay relatively the same?
Yes
What is speed?
Distance that a moving object covers in a unit of time.
What is acceleration?
The change in speed divided by the time during which the change takes place.
What is work?
Done when an object is moved over a distance
What is work denoted by?
Joule and measured in N/M
What is the equation for power?
Work over time.
What is the speed of sound denoted by?
a
In the formula for speed of sound what is the number 20?
Approximation of the total of all the relevant constant values.
In the formula for speed of sound what is the temperature always expressed in?
kelvin
Formula for speed of sound?
a= 20 x (square root of) T(m/s)
If the temperature is lower what happens to the speed of sound?
Lower
