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Homework Help: Confused about the units of density

  1. Apr 13, 2010 #1
    1. The problem statement, all variables and given/known data
    I'm dealing with densities of liquids.

    When using the formula P = Patm + ϱgh, where ϱ is the density of the liquid, what should the units of ϱ be?

    2. Relevant equations

    3. The attempt at a solution
    I have P in kPa, so just looking at the units gives:
    kPa = kPa + (?)(m/s2)(m) --> kPa = (?)(m2/s2)

    Which would mean the units of ϱ are (kPa)(s2 / m2).

    Somehow that seems wrong... I thought ϱ was supposed to have units of mass per volume?
  2. jcsd
  3. Apr 13, 2010 #2


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    Homework Helper

    1 Pa = 1 N m-2
    1 kPa = 1000 Pa
    1 atm = 101.325 kPa

    1 N=1kg m s-2

    So 1 atm = 101325kg m-1s-2 in the basic Si units.

  4. Apr 13, 2010 #3


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    kPa has the same unit as Pa, which can be written as N/m2
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