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Dirac delta dimensionless?

  1. Sep 7, 2011 #1
    Probably a trivial question, but does Dirac delta function has (to have always) a physical dimension or is it used just as a auxiliary construct to express e.g. sudden force impulse, i.e. Force = Impulse \times \delta, where 'Impulse' carries the dimension?
    Any comments would be highly appreciated.
    FP
     
  2. jcsd
  3. Sep 7, 2011 #2

    BruceW

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    When people use the word 'Dirac delta function', they usually mean the function which acts like this:
    [tex] \int_{- \infty}^\infty f(t) \delta(t-T)dt=f(T)[/tex]
    Which is something different to what you're talking about. If I'm right, you're talking about Impulse=force times (small time interval), i.e.
    [tex]I=F \ \delta t [/tex]
    In this case, the delta just signifies that the time interval is very small, and if we take it to be infinitesimally small, we get:
    [tex]dI=Fdt[/tex]
    Which allows us to calculate the change in momentum when a non-constant force is applied.

    So in this case, the delta carries the dimension of time. But I guess the use of delta doesn't always have to have dimension. (For example, it could be used to express a small change in some dimensionless ratio of parameters).
     
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