EXAMPLE 1-4 The Weight of One Pound – Mass
Using unity conversion ratios, show that 1.00 lbm weighs 1.00 lbf on earth (Fig.1-40).
SOLUTION A mass of 1.00 lbm is subjected to standard earth gravity. lts weight in lbf is to be determined.
Assumptions standard sea-level conditions are assumed.
Properties The gravitational constant is g = 32.174 ft/ .
Analysis We apply Newton’s second law to calculate. The weight (force) that corresponds to the known mass and acceleration. The weight of any object is equal to its mass times the local value of gravitational acceleration. Thus,
W = mg = (1.00 1bm)(32.174 ft/ ) = 1.00
Discussion The quantity in large parentheses in this equation is unity conversion ratio. Mass is the same regardless of its location. However, on some other planet with a different value of gravitational, the weight of 1 lbm would differ from that calculated here.