Pressure Equation Confusion

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austinwilcox Participant Join Date: Jan 2009 Posts: 1	Pressure Equation Confusion 01/09/2009 11:14 AM
	The classic equation for pressure at depth is P=rgh but most on line calculators use P=rh, what am I missing? I'm working on a hoop stress equation for a fabric water tank and kept getting crazy answers from HS=PD/2t so I went on line to check my numbers and noticed that every web calculator I could find used P=rh to calculate pressure, even if the P=rgh equation was listed right next to the calculator. When I checked for known pressures at depth to check the calculators, all the answers I could find match the P=rh formula, while every equation I could find matches P=rgh. This should be simple but now I'm just confused.
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V.Daniel Associate Join Date: Nov 2007 Location: Tijuana, MX Posts: 40 Good Answers: 2	#1 Re: Pressure Equation Confusion 01/09/2009 12:02 PM
	Are you using imperial units? lbs are treated as both force and mass, hence, no need to multiply by g.
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omargelvez Member Join Date: Jan 2009 Posts: 8	#2 Re: Pressure Equation Confusion 01/10/2009 8:05 PM
	by dimensional analisis you can see: P=r(Kg/m3).g(m/sg2).h(m) you obtain P(Kgm/sg2)/m2 = N/m2=Pa. if you use only P=r.h you obtain P en Kgf/m2. P=rgh is the pressure due to internal fluid, HS=PD/2t is the stress in the material of the container due to the pressure P
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