Physics
What you must know
Physics for aircraft maintenance covers matter and its states, mass versus weight, density and specific gravity, force, moments and couples, pressure (including gauge versus absolute), work, power and energy, heat and temperature scales, and basic mechanics of solids, liquids and gases. You should understand the gas laws qualitatively, thermal expansion, and the difference between static and dynamic pressure as used in pitot-static systems.
Traps to watch
- Mass versus weight: mass in kg is constant; weight is force in newtons (W = mg, g ≈ 9.81 m/s²).
- Pressure units: 1 bar = 100 kPa; absolute pressure = gauge pressure + atmospheric pressure. A gauge reading of zero means atmospheric, not vacuum.
- Moments: the moment arm is the perpendicular distance from the pivot to the line of action of the force, not along the lever.
- Heat versus temperature: heat is energy transferred; temperature is a measure of average kinetic energy. Specific heat capacity links them.
- Density and specific gravity: specific gravity is dimensionless (density relative to water); it is numerically equal to density in g/cm³.
Worked example
A force of 200 N acts at 90° to a spanner at a perpendicular distance of 0.25 m from the nut. Moment = F x d = 200 x 0.25 = 50 N·m. If the force were applied at 30° to the lever, only the perpendicular component (F sin 30° = 100 N) creates moment, giving 25 N·m.
Rule of thumb
For any moment problem, resolve the force into the component perpendicular to the arm before multiplying by distance.