Final answer:
The appropriate cruising altitude for flights adheres to regulations and safety measures, such as maintaining specific distances from other airplanes and considers factors like air density for lift. Air traffic control dictates the flight path within these parameters to ensure safety and efficiency during flight.
Step-by-step explanation:
The determination of the appropriate altitude for cruising flight in the Northern Domestic Airspace takes into account various factors including air traffic regulations, safety requirements, and the physical principles such as Bernoulli's principle influencing aircraft lift. For safety, each airplane must maintain a distance of five miles from other planes flying at the same altitude and observe vertical separation of 2,000 feet (or 1,000 feet if below 29,000 feet altitude). The flight path and altitude also consider optimal aerodynamic conditions to create lift, with adjustments for factors like air density at different altitudes.
Regarding the latter part of the question, the air speed over the upper surface of a wing has to be faster than under the wing to create lift, according to Bernoulli's principle. At cruising speed and an altitude where air density is one-fourth that at sea level, the aircraft would require adjustment of speed and wing design to maintain the necessary lift, considering that some lift also comes from the aircraft's body, engine thrust, and other sources.