Final answer:
Physics discusses the need for oxygen at high altitudes due to decreased air pressure and oxygen levels. At cabin-pressure altitudes above 12,500 feet ASL, supplemental oxygen is required. The volume of air in the body will also expand in response to the reduced pressure at higher altitudes.
Step-by-step explanation:
The subject of this question is physics, specifically concerning altitude and its effects on the body and atmospheric pressure. At cabin-pressure altitudes above 12,500 feet ASL, supplemental oxygen is required for the occupants of an unpressurized aircraft. This is necessary to prevent hypoxia, a condition where the body is deprived of adequate oxygen supply at the tissue level.
The concept of changing pressure at different altitudes can be seen in other examples as well. For instance, an airplane passenger's stomach that contains 100 cm³ of air at sea-level will expand to a larger volume at a cruising altitude where the cabin pressure drops to 7.50 × 104 N/m² due to Boyle's Law, which states that pressure and volume are inversely proportional when temperature and the amount of gas remain constant.
Altitude sickness is a likely result of rapid ascent to elevations above 2,500 meters due to reduced air pressure and oxygen levels which can upset the balance of pH and bicarbonate concentration in the blood. Proper acclimatization is necessary to prevent serious health risks.