What is the primary purpose of a Pitot tube?

The primary purpose of a Pitot tube is to measure ram air pressure. This device is crucial in aviation as it directly measures the dynamic pressure of the air as the aircraft moves through it. The Pitot tube is typically located on the exterior of the aircraft and is designed to face the airflow, allowing it to capture the pressure created by the aircraft's forward motion.

This ram air pressure is essential for calculating airspeed, as it derives the difference between the total pressure experienced at the front of the tube and the static pressure (which can be measured with a separate static port). By interpreting ram air pressure in conjunction with static pressure, pilots and aircraft systems can determine true airspeed and other flight parameters.

The other choices relate to different measurements that are not the primary function of a Pitot tube. While altitude and static pressure are important in flight, they fall under different measurement systems and instruments (like altimeters and static ports) rather than being the direct purpose of the Pitot tube itself. Calculating aircraft weight is unrelated to the function of a Pitot tube as it requires separate instrumentation and methods entirely.