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Worked example 1.2: Tire pressure

Question: The recommended tire pressure in a Honda Civic is 28 psi (pounds per square inch). What is this pressure in atmospheres (1 atmosphere is $10^5 {\rm N} {\rm m}^{-2}$)?
Answer: First, 28 pounds per square inch is the same as $28\times (12)^2 = 4032$ pounds per square foot (the standard fps unit of pressure). Now, 1 pound equals $4.448$ Newtons (the standard SI unit of force), and 1 foot equals $0.3048$m (see Tab. 2). Hence,

P = 4032\times (4.448) / (0.3048)^2 = 1.93\times 10^5 {\rm N}{\rm m}^{-2}.

It follows that 28 psi is equivalent to $1.93$ atmospheres.

Richard Fitzpatrick 2006-02-02