Trivial question on head loss conversion.

[dbecker]

I am trying to convert head loss of feet into corresponding pressure drop in psi.

If I multiply the height in feet by density which is in units of lbm/ft^3, then my result will not be pounds force per square foot, but pounds mass per square foot (this is not pressure!!!).

Am I missing something here?

Thanks

 

[gmax137]

Maybe this is obvious to everyone else, but it helps me to remember that the reason the 'customary pound' units are the way they are is this: normally (ie, here on the surface of the earth) a pound mass weighs a pound (force). The problem is, if you apply a force of 1 lbf to a mass of 1 lbm, it does not accelerate at 1 ft/sec2; in fact it accelerates at 32.2 ft/sec2.

That's really the source of all (my) confusion, and the reasons why the units are set up to confuse me. Like I said, understanding that helps me put the 32.2 in where it goes.

 

[BigInch]

Actually that depends in which direction the force is applied and acceleration would be 33.2 ft/sec, if the force was applied downward not 32.2.

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