1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Lb/f to kn/m and not consistent

  1. Jun 3, 2013 #1
    I'm trying to convert lb/f to kn/m.
    A concrete has weight of 23.54 kilonewton/cubic meter which is equal to 150 pounds per cubic feet.

    For a beam with the following dimensions
    width = 0.3m = 0.84 feet
    depth = 0.5m = 1.9685 feet

    for the beam weight per meter in metric, it is 23.54*0.3*0.5=3.531 kn/m
    for the beam weight per foot in english, it is 150*0.98*1.96=290.62 lb/foot

    But if I convert 290.62 lb/foot to kn/m. I don't get 3.531kn/m but 4.240181 kn/m
    here's the calculation

    290.62 lb/f * 3.28 f/m * 1kn/224.8lb = 4.24 kn/m

    why not 3.531 kn/m??

    Note this is not a homework. Thanks.
  2. jcsd
  3. Jun 3, 2013 #2
    I didn't check the calculation, but I noticed you wrote 0.84 feet for the width but used 0.98 feet in a calculation a few lines down. Maybe that is where the error lies?
  4. Jun 4, 2013 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    I don't know where you got your meter and feet conversions from, but they are in error.

    1 meter = 39.37 in. = 3.2808 ft.

    1 foot = .305 m
  5. Jun 4, 2013 #4
    i got the error. It's formula in my excel which uses 0.6m instead of 0.5m. Anyway, thanks
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook