8.1

Aerodynamics is derived from Greek words aero (air) and dyne (force of power), defining the study of objects in motion through air and the forces producing or changing that motion.
Aircraft aerodynamic definition: An object traveling through space affected by atmospheric conditions, governing the relationships between aircraft, relative wind, and atmosphere.
Key physical difference between water and air: Air is compressible, whereas water is incompressible.

Air composition: Primarily nitrogen and oxygen, behaving as a fluid that flows and fills containers.
Pressure formula: $F = A \times P$ or $P = \frac{F}{A}$ .
Standard atmospheric pressure at sea level equals:
- $1\,\text{atm}$
- $14.7\,\text{psi}$
- $29.92\,\text{in Hg}$
- $1013.2\,\text{hPa}$ ( $101\,325\,\text{N/m}^2$ )
- $1013.2\,\text{mb}$
- $760\,\text{mm Hg}$

Atmospheric pressure drops rapidly with increasing altitude; at $50\,000\,\text{ft}$ , pressure drops to approximately one-tenth of sea-level value ( $2.72\,\text{psi}$ at $40\,000\,\text{ft}$ ).

Density variation rules:
- Direct proportion with pressure.
- Inverse proportion with temperature.
- Inverse proportion with humidity.
Altitude and density: High-altitude air is less dense than low-altitude air; lower air density reduces resistance, allowing aircraft to fly faster.
Moisture impact: Water vapor weighs approximately five-eighths ( $\frac{5}{8}$ ) as much as an equal volume of dry air. Damp air is less dense than dry air, requiring longer takeoff runway distances.

Troposphere: Lowest layer extending from surface to an average of $38\,000\,\text{ft}$ ( $25\,000\,\text{ft}$ -- $30\,000\,\text{ft}$ at poles, $60\,000\,\text{ft}$ at equator).
- Lapse rate: Temperature decreases at approximately $-2\,^{\circ}\text{C}$ ( $-3.5\,^{\circ}\text{F}$ ) per $1\,000\,\text{ft}$ of altitude increase.
Tropopause: Upper boundary of