Problem: Room temperature atmospheric air flows at 100 feet per second in a 400 foot long nominal 3-inch schedule 40 threaded steel pipe containing 12 90-de...
Given: 100 feet per second in a 400 foot long nominal 3-inch schedule 40 threaded steel pipe containing 12 90-degree long ra...
Approach: So this one's a bit interesting because the fluid is not water.
Key formula: formula for this which you can look up in the reference handbook or the murm and I'll show you a little shortcut at t...
Calc: We're going from 1 to 2 and at 2 the elevation is 200 feet lower.
Calc: So here's 1 and here's 2 and let's just suppose that that's the horizontal line and this distance in between the two is a coupl...
Result: result of that is p1 minus p2 and that's what we're after what's the pressure difference between the two ends of the pipe p1 minus p2 equals 53 59 ...
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Student questions asked in live office hours about this problem
OH 120 · May 11, 2026
Q: Is it acceptable to use 0.075 lb/ft³ as the specific weight of air, and what is the technical distinction between lb_mass/ft³ and lb_force/ft³?
A: Using 0.075 lb_f/ft³ for the specific weight of air is acceptable, but lb_mass/ft³ is density while lb_force/ft³ is specific weight — they are not the same term. The conversion between them involves multiplying by g/g_c, which is what allows you to go from pound-mass to pound-force; you can skip that step in practice as long as you understand that conversion is happening in the background.