Final answer:
Altimeter 2 refers to a secondary or backup altimeter in aircraft, which measures altitude above sea level. The altitude-air density relationship is important as it affects an aircraft's performance, with air density decreasing as altitude increases.
Step-by-step explanation:
The term Altimeter 2 likely refers to the second altimeter in an aircraft, often the secondary or backup altimeter. An altimeter is an instrument used to measure the aircraft's altitude above sea level. As per the provided information, the relationship between altitude and air density is shown in a line graph where the altitude is measured in meters above sea level, and air density is measured in kilograms of air per cubic meter. As altitude increases, the air density decreases, which is crucial for altimeter readings. For example, the point at the top of Mount Everest is said to have an altitude of approximately 8,828 meters and an air density of 0.023 kilograms per cubic meter. When pilots fly, they need to be aware of the air density, as it affects the performance of the aircraft. Furthermore, the rate at which air density decreases per 1,000 meters of altitude gain can be calculated using the slope determined by points at 4,000 meters and 6,000 meters altitude.
Altimeters are also used in the context of fluid dynamics, where they can help measure various fluid velocities and are closely related to the principles of air density and air speed indicators, such as those used in aircraft for navigation and safety purposes.