Measuring air speed. An airplane pilot must always know her speed relative to the surrounding air. Air speed that is too low can cause the plane to stall, whereas air speed that is too high can cause so much stress on the wings or rudder that they fail. GPS systems cannot be used to measure air speed; they can only measure speed relative to the ground. Instead, a device called a pitot tube (Fig. P10.97, left) is used. Invented in the 18th century, a pitot tube determines the air speed v from the pressure difference p₁- p₂in Figure P10.97, right. Here the plane is flying toward the left, and the air speed is zero in the central tube (where the pressure is p₁) and v across the opening at the top where the pressure is p₂. 

(a) Is p₁ - p₂ positive or negative? 

(b) Use Bernoulli’s equation to calculate this pressure difference for an airplane traveling with an air speed of 250 m/s (about 500 mph).

Figure P10.97

 

Transcribed Image Text:

Wind P2 P1 Pressure gauge