Let's see your attempt at doing some of the units conversions, starting with the 2nd equation. If RHO is given as 10 ppg, what is density in ##lb_m/ft^3##? What is it in slugs/ft^3?morty92222 said:Homework Statement
h = 10 ft
RHO = 10 ppg (or pounds/gallon)
Homework Equations
P = 0.052 * RHO * h
P = RHO * G * h
I am very confused right now as why each equation gives a different answer! What are the correct units for the 2nd equation and how do I convert from second equation to the first one? And where does the g goes?! I looked it up online and but they just say "RHO" takes care of it! What does that mean?!
Thank you!
I asked for the density in slugs/ft^3.morty92222 said:So 10 ppg equals 74.8 lb/ft3. What should I use for g in the second equation (in terms of units)?
I never heard about "slug" in my entire life. After googling it, it appears to be 2.33 slug/ft3. But I don't have any feel for the unit or what it represents.Chestermiller said:I asked for the density in slugs/ft^3.
A slug is what you use if you are using English units, and you want to write F = ma (without a correction factor), with F in pounds force, mass in slugs, and acceleration in ft/sec^2. So, with g = 32.2 ft/sec^2, what do you get for the pressure using ##P=\rho g h##?morty92222 said:I never heard about "slug" in my entire life. After googling it, it appears to be 2.33 slug/ft3. But I don't have any feel for the unit or what it represents.
Chestermiller said:A slug is what you use if you are using English units, and you want to write F = ma (without a correction factor), with F in pounds force, mass in slugs, and acceleration in ft/sec^2. So, with g = 32.2 ft/sec^2, what do you get for the pressure using ##P=\rho g h##?
You just use rho g h to get the pressure. Slugs IS mass.morty92222 said:I am not sure how to use the slug in P=Rho g h as there is no mass in there!
Chestermiller said:You just use rho g h to get the pressure. Slugs IS mass.
It is the same as slug-ft/(ft^2 sec^2). 1 slug-ft/(sec^2) = 1 lb_f. So the unit are lb-f/ft^2=psf. What units did you want the answer in?morty92222 said:So 2.33 * 32.2 *10 = 750 [slug/(ft. sec2)]
What kind of units is this?
Chestermiller said:It is the same as slug-ft/(ft^2 sec^2). 1 slug-ft/(sec^2) = 1 lb_f. So the unit are lb-f/ft^2=psf. What units did you want the answer in?
Don't despair. You just got to get used to manipulating the units. Are you familiar with the use of ##g_c=32.2\ \frac{lb_m\ ft}{lb_f\ sec^2}##?morty92222 said:I actually wanted the answer in psi so I can compare it to P = 0.052 * ppg * h = 0.052 * 10 * 10 = 5.2 psi
Edit: So 750/144 = 5.2 psi! Thank you so much.
I still do not understand how we reached this conclusion! :D You kinda took me through it that I don't even understand what was wrong in the first place.