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Unit converions

  1. Oct 25, 2007 #1
    i know this is a basic question but i need some assistance abut unit conversions. i want to know how to convert something like, say, 120km/hr to m/s but the way my teacher explains it is too confusing. i just want to know is there a simpler way to convert somthing like that easliy?
     
  2. jcsd
  3. Oct 25, 2007 #2
    You want to use dimensional analysis. The basic idea behind dimensional analysis is that you use equalities until you get the units you want. Let's take your example then

    1km = 1000m

    so divide by either 1000m or 1km depending on the situation, so you get an equality of 1. In this case we want kilometers on the bottom (denominator) so it cancels the kilometers up top (numerator).

    1000m/1km = 1

    so now we go the kilometer per hour equation and multiply it by 1 i.e. our equality

    [tex]1\frac{km}{h} * \frac{1000m}{1km} = \frac{1000m}{h}[/tex]

    Then you just continue on down the line

    [tex]1\frac{km}{h} * \frac{1000m}{km} * \frac{1h}{60min} * \frac{1min}{60s} = \frac{1000 m}{3600s}[/tex]

    Make sense?

    EDIT:
    There are probably a lot of threads like this that can give you some examples, but I know of another because I thought it was kind of cool what the guy was looking for once I understood his question.

    https://www.physicsforums.com/showthread.php?t=177566&highlight=dimensional+analysis
     
    Last edited: Oct 25, 2007
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