Show that the variation of atmospheric pressure with altitude is given by P = P 0 e − αy where α = ρ 0 g/P 0 , P 0 is atmospheric pressure at some reference level y = 0, and ρ 0 is the atmospheric density at this level. Assume the decrease in atmospheric pressure over an infinitesimal change in altitude (so that the density is approximately uniform over the infinitesimal change) can be expressed from Equation 14.4 as dP = − pg dy . Also assume the density of air is proportional to the pressure, which, as we will see in Chapter 18, is equivalent to assuming the temperature of the air is the same at all altitudes.
Show that the variation of atmospheric pressure with altitude is given by P = P 0 e − αy where α = ρ 0 g/P 0 , P 0 is atmospheric pressure at some reference level y = 0, and ρ 0 is the atmospheric density at this level. Assume the decrease in atmospheric pressure over an infinitesimal change in altitude (so that the density is approximately uniform over the infinitesimal change) can be expressed from Equation 14.4 as dP = − pg dy . Also assume the density of air is proportional to the pressure, which, as we will see in Chapter 18, is equivalent to assuming the temperature of the air is the same at all altitudes.
Solution Summary: The author explains that atmospheric pressure is a pressure exerted by the weight of the atmosphere.
Show that the variation of atmospheric pressure with altitude is given by P = P0e−αy where α = ρ0g/P0, P0 is atmospheric pressure at some reference level y = 0, and ρ0 is the atmospheric density at this level. Assume the decrease in atmospheric pressure over an infinitesimal change in altitude (so that the density is approximately uniform over the infinitesimal change) can be expressed from Equation 14.4 as dP = −pg dy. Also assume the density of air is proportional to the pressure, which, as we will see in Chapter 18, is equivalent to assuming the temperature of the air is the same at all altitudes.
The pressure on Earth's atmosphere as a function of height y above sea level can be determined by
assuming g to be constant and that the density of air is proportional to the pressure, i.e., px P.
Note that this assumption is not very accurate since temperature and other weather effects can
influence pressure. [Hint: Po = 1.013 × 105 N/m², po = 1.29 kg x m-³]
(1) Start by finding a relation between the pressure Po and the density of air po at 0° at sea level
(y=0) and the pressure P and density p at height y. Using this relation find an expression
for p as a function of P, i.e., p = p(P).
(2) Find the pressure as a function y.
(3) At what altitude above sea level is the atmospheric pressure equal to half the pressure at sea
level?
The density of air is 1.3 kg/m at sea level. From your knowledge of air pressure at ground level, estimate the height of the atmosphere. As a simplifying assumption, take the atmosphere to be of
uniform density up to some height, after which the density rapidly falls to zero. (In reality, the density of the atmosphere decreases as we go up.) t
O 1 km
O 10 km
O 100 km
O 1000 km
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An airplane passenger has a volume V1 of air in his stomach just before the plane takes off from a sea-level airport.
What volume will this quantity of air have at cruising altitude at the same temprerature ( body temp. ), in terms of V1, the pressure on the ground P1, and the cabin pressure at cruising altitude P2?
What is this volume, in cubic centimeters, if the initial volume is 110 cm^3 and the cabin pressure drops to 7.5x10^4 Pa when the plane is at cruising altitude?
Chapter 14 Solutions
Physics for Scientists and Engineers, Technology Update (No access codes included)
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