# The density of air decreases with height above the Earth, and when the density is too low, people get sick

## Question:

The density of air decreases with height above the Earth, and when the density is too low, people get sick or even become unconscious. That is why the cabins of commercial airplanes are ?pressurized? during flight. Cabin pressure, however, is lower than the pressure at sea level. Cabins typically have a pressure equal to the air pressure at an altitude of about 8000 ft above the Earth?s surface. This reduced pressure is one reason some people feel fatigued after a long flight.?

(a) Use Equation 10.11 to calculate this cabin pressure.?

(b) Estimate the total net force on the walls of a Boeing 737 flying at 35,000 ft. Approximate the airplane as a cylinder of length 30 m and diameter 4 m. You will need to estimate the air pressure outside the plane using Figure 10.15.?

(c) What would the force on the walls be if the cabin pressure equals the pressure at the Earth?s surface?

Figure 10.15

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