30 Questions
Which of the following best defines the atmosphere?
A physical mixture of gases that surrounds the Earth
What is the pressure on the Earth's surface at sea level?
14.69 psi
Which region of the atmosphere is of little importance for commercial aircraft?
Exosphere
What is the composition of the atmosphere?
Several separate gases that remain constant regardless of altitude
What is the region between 20,000 feet and 60,000 feet above sea level called?
Tropopause
Which pressure measurement is referenced from zero rather than from atmospheric pressure?
Absolute pressure
What is the formula for density?
$Density = Mass/Volume$
What is the rate of temperature change in the troposphere for every 1000ft of altitude change?
1.98°C
What is the sum of static and dynamic pressure called?
Total pressure
What is the metric unit of measure for barometric pressure?
Millibars
Which layer of the atmosphere marks the ceiling of the troposphere?
Tropopause
What is the approximate altitude of the tropopause over the equator?
60,000 ft
Which organization has agreed upon the International Standard Atmosphere (ISA)?
International Civil Aeronautics Organisation (ICAO)
What is the air pressure at sea level according to the International Standard Atmosphere (ISA)?
1013.25 millibars
What is the standard temperature lapse rate up to 40,000 feet in altitude?
1.98°C decrease every 1,000 feet
What happens to the density of air as altitude increases?
The density decreases
How does lower air density affect the aerodynamic performance of an aircraft?
It decreases the lift
What is the relationship between air density and pressure ?
Direct proportion
Why does an aircraft require a longer runway for take-off on damp days?
The air density is lower on damp days
Which of the following statements about acceleration due to gravity is correct?
Acceleration due to gravity varies slightly at different parts of the earths surface.
Which of the following best describes viscosity?
Viscosity is a property of both liquids and gases.
Which of the following best describes the relationship between viscosity and pouring time?
The higher the viscosity, the longer the pouring time.
Which of the following statements is true about viscosity?
Viscosity is the property of a fluid that offers resistance to the relative motion of its molecules.
What is the velocity of a stationary boundary in a fluid?
0
What is the net result of more momentum being carried in one direction than the other?
Forces between the layers retard the faster moving layers and accelerate the slower moving ones.
What is a boundary layer in a fluid?
A thin layer of fluid between a fixed and moving boundary, across which a velocity change takes place.
What are the energy losses due to friction within a fluid dependent on?
The viscosity of the fluid.
What is the relationship between velocity change and viscosity in a fluid?
Velocity change in a fluid is directly proportional to its viscosity.
What Percentage of nitrogen is in the atmosphere?
78%
How do you calculate dynamic pressure ?
1/2 pv2
Study Notes
Composition and Layers of the Earth's Atmosphere:
- The air surrounding the Earth is a physical mixture of gases and is considered a fluid.
- The atmosphere extends upward for approximately 500 miles (804 km) and exerts pressure on everything on the Earth's surface.
- The atmosphere is divided into four concentric gas layers: Troposphere, Stratosphere, Ionosphere, and Exosphere.
- The Tropopause is the region between the troposphere and stratosphere where most fixed-wing aircraft operate.
- The Tropopause varies in altitude, with an average of around 35,000 feet in temperate latitudes.
- The International Standard Atmosphere (ISA) serves as a reference for aerodynamic computations and provides standard atmospheric conditions.
- The ISA is based on a sea level temperature of 15°C (59°F) and a barometric pressure of 29.92 inches of mercury (inHg).
- The air pressure decreases with an increase in altitude, with a decrease of 2 psi for every 5,000 feet.
- Air density at sea level is 1.225 kg/m3 (0.77 lbs/ft3).
- Temperature decreases with altitude at an average rate of 1.98°C (3.5°F) per 1,000 feet up to 40,000 feet.
- Pressure is caused by the Earth's gravity pulling a column of air towards the surface, and there are different ways to measure it (psi, inHg, mb, pa).
- Altimeters measure absolute pressure and display the result in feet above sea level.
Test your knowledge on the relationship between density, pressure, and temperature in this quiz. Learn why air at high altitudes is less dense than air at low altitudes and how changes in density affect the aerodynamic performance of an aircraft. Challenge yourself and see how well you understand the concepts of air density and lift.
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