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Homework Help: Some help with Si Unit conversions

  1. Aug 29, 2011 #1
    Some help with Si Unit conversions :)

    1. The problem statement, all variables and given/known data

    762 Mg/m to ng/µm

    2. Relevant equations

    Si unit conversions

    3. The attempt at a solution

    How do I know where to place the variables? Can someone give me a tut or written explantion on how to do this?
  2. jcsd
  3. Aug 29, 2011 #2


    User Avatar

    Staff: Mentor

    Re: Some help with Si Unit conversions :)

    Welcome to the PF.

    Yes, there is a very straightforward way to do unit conversions. But first, you need to be careful to be precise in what you are asking. Are you really wanting to convert from Megagrams/m to nanograms/um? Or did you mean to write milligrams/nm to miccrograms/um. Megagrams is not a unit that is used very much.

    In either case, the trick is to multiply the quantity you want to convert units on by "1". But you make it a very special "1".

    To convert 5m/s to km/s, you multiply by 1 = 1km/1000m

    5m/s * 1 = 5m/s * 1km/1000m = 0.005km/s

    To convert 2km/s to m/s, you multiply by 1 = 1000m/1km

    2km/s * 1 = 2km/s * 1000m/1km = 2000m/s

    You carry the units along in the equation, and cancel like units that show up in the numerator and the denominator. So when you are figuring out the form of the "1" fraction that you want to multiply by, put the units you want to end up with in the numerator, and the ones you want to cancel out in the denominator.

    Makes sense?

    EDIT -- Also, when you want to convert units in the denominator, you follow the analogous procedure. Just keep multiplying by an appropriate "1" fraction to be able to cancel out the old units and be left with the new units in the position you want them in the fraction.
    Last edited: Aug 29, 2011
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