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Units and Dimensions

  1. May 10, 2012 #1
    1. The problem statement, all variables and given/known data

    Assuming that Pressure (P) of a particle is given by

    P = b - t^2 / ax

    where t = time, x = position
    Find the dimension of b/a.

    2. Relevant equations

    3. The attempt at a solution

    Using dimensional homogenity, I know that b represents time interval.
  2. jcsd
  3. May 10, 2012 #2
    Is this (b-t2)/ax or b - (t2/ax)?

    If it is the first, there is a subtraction of two quantities. Subtraction of what two quantities gives pressure? What does that tell you about b? and (t2/ax)?

    If it's the second, what should be the dimension of b so that (t2/ax) can be subtracted from it? (apples and oranges? or, apples and apples? :wink:)
  4. May 10, 2012 #3


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    Staff: Mentor

    Assuming you have represented the formula correctly .....
    I don't think so. qcPcD.gif ...

    your equation shows P comprising the sum of two components: b and (- t^2 / ax). Those two components must have identical units otherwise you couldn't add them, and what's more, they must have the same units as P.

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