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Any structural Engineers? Need to convert kN/m3 to kg/m3

Discussion in 'General Chat Forum' started by Laubi02, Oct 22, 2012.

  1. Laubi02

    Laubi02 Well-known Member

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    I've got the typical density of reinforced concrete - 17 to 24kN/m3. But I need it in kg/m3 format. anyone know how to do this?
     
  2. MIghtyG

    MIghtyG Well-known Member

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    Density in newtons per meter cubed!?! weird :laugh:

    afaik it should be a case of g=9.81ms^-2

    and F=M.A so M=F/A (Keep in mind Newtons are the SI unit for force and Kg are the SI unit for mass)

    17000/9.81=1732kg/m^3 to 24000/9.81=2446kg/m^3
     
  3. nheather

    nheather Distinguished Member

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    They are different dimensioned units. One is a mass per cubic metre and one is a force per cubic metre.

    The most common way of converting a static mass to a force is to multiply it by the acceleration due to earth's gravity. An easy rule of thumb is 10 but more accurately it is 9.81.

    Cheers,

    Nigel
     
  4. nacmacfeegle

    nacmacfeegle Well-known Member

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    1700-2400 kg/m3 approx.
    Density isn't normally quoted in N/m3 though, dunno why it is here.
     
  5. DPinBucks

    DPinBucks Well-known Member

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    1kgf (kilogram of force) = 9.807 Newtons. So to convert kN to kg, divide by 9.807.

    Strictly speaking, that's only meaningful in standard gravity, but the conversion factor applies universally.

    ===== EDIT ====
    MightyG's done it for you.
     
    Last edited: Oct 22, 2012
  6. nheather

    nheather Distinguished Member

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    Sorry, pedant alert.

    It can't apply universally because it varies greatly depending on where you are in the universe. ;)

    Cheers,

    Nigel
     
  7. nacmacfeegle

    nacmacfeegle Well-known Member

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    It will vary depending on where you are on earth and at what altitude, but when we have a huge variation on the specified density, who cares?:)
     
  8. DPinBucks

    DPinBucks Well-known Member

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    A pedant replies:

    No, it doesn't. :)

    Newtons and kilograms are arbitrary units. Note that I defined the conversion in terms of kgf, not kg. kg are units of mass, which are universal. Newtons are arbitrarily assigned to kg mass on Earth. The same principle applied on another planet wouldn't be Newtons. But Newtons on Mars are still Newtons. They're not very useful there, that's all.
     
  9. Laubi02

    Laubi02 Well-known Member

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  10. logiciel

    logiciel Moderator

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    kN=1000*kg*m/s*s so kg=kN*s*s/1000*m
     
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