Final answer:
Flying higher increases fuel consumption because additional energy is needed to lift both the airplane and the fuel against Earth's gravity. Overcoming air resistance also contributes significantly to fuel consumption, independent of how many passengers are aboard. The efficiency of fuel usage varies with the number of passengers, with fully occupied planes being more fuel-efficient per passenger.
Step-by-step explanation:
Flying higher increases fuel consumption due to the energy required to lift the fuel itself away from the Earth's gravity. This is similar to space travel, where escaping Earth's gravity necessitates a substantial fuel load, underscoring the fact that fuel requirements do not simply scale with distance as they might in a car on a road trip. Additionally, an airplane has to overcome air resistance, which is primarily a function of the airplane's size and speed and is relatively independent of the passenger load. Consequently, the energy used to fly a plane from one point to another remains almost the same regardless of how many passengers are on board.
Considering the mass of fuel and the importance it has compared to the car's mass, we can understand that additional energy is needed to transport not just the aircraft but the fuel itself. The topic of fuel efficiency in transportation illustrates the complexity of factors, such as mass and resistance, and their impact on energy consumption, especially when considering the environmental implications of increased CO₂ emissions.
Passenger jet fuel economy is also affected by how full the flight is, with full planes being more efficient on a per-passenger basis than those which are not fully occupied. For instance, a typically full passenger jet can achieve around 90 miles per gallon per seat, decreasing to 45 miles per gallon per passenger if the plane is only half-full. This is an important concept when comparing the energy cost of air travel to that of road travel in a car.