Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Oh my delta!

  1. Apr 12, 2006 #1
    I know [tex]\Delta W[/tex], [tex]dW[/tex], [tex]\partial W[/tex]. But what does [tex]\delta W[/tex] exactly mean? How does it differ from the previous ones?
  2. jcsd
  3. Apr 12, 2006 #2


    User Avatar

    Staff: Mentor

    Is that the Dirac delta? Where have you seen the symbol?
  4. Apr 12, 2006 #3
    Of course it's not Dirac delta.
    Classical mechanics book. It's somekind of infintesimal change in work.
  5. Apr 12, 2006 #4


    User Avatar

    Staff: Mentor

    Okay, whatever. What does this classical mechanics book say about it? How is it used differently compared to the first delta symbol in your original question?
  6. Apr 12, 2006 #5


    User Avatar
    Science Advisor

    Then ask in a physics forum, not mathematics.
  7. Apr 12, 2006 #6
    It's mathematical operator.
    Replace the W with something else if you like. Satisfied?
  8. Apr 12, 2006 #7


    User Avatar

    Staff: Mentor

  9. Apr 12, 2006 #8


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    Dearly Missed

    The VARIATION of a quantity W is very often written as [itex]\delta{W}[/itex]
  10. Apr 12, 2006 #9
    Whoops! Sorry, I didn't notice your post. Really sorry!
    That notation pops-up in many places, especially in Lagrangian. I've had a quick look at wikipedia, and found http://en.wikipedia.org/wiki/Lagrangian" [Broken] (at the bottom of the page). I just though this a famous-to-all notation.

    I had this somewhere in my after reading https://www.physicsforums.com/showpost.php?p=949279&postcount=15" of Clasius2. I was actually looking for a rigorous definition of it, from the standpoint of a mathematician.
    Last edited by a moderator: May 2, 2017
  11. Apr 12, 2006 #10


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    That notation falls into the category of symbolism which is defined as you go. Different authors will use it in different ways. It does not have a standard mathematical definition, being a parameter of a physical system which should be defined or clear from context when it is used.

    In the link to the Lagrangian you provided it is used to state the "Least action principle". To understand it's meaning you will need to research that term since the author of the article assumes you know about that. So when you understand least action principle then you will understand how it is used in that context.
  12. Apr 14, 2006 #11


    User Avatar
    Science Advisor
    Homework Helper

    It stands for the G^ateaux derivative of the action integral.

  13. Apr 14, 2006 #12
    It's the differential of a functional.

    You have a "functional", a function defined on a space of functions (paths in configuration space). This function assigns to each path, a real scalar, the work associated with that path. Remember with ordinary derivatives, you look at the displacement dy resulting from an infinitesimal dx. There's an analagous concept with functionals, the infinitesimal [itex]\delta W[/itex] associated with an infinitesimal change in path [itex]\,\delta J[/itex] (or whatever notation you use). Look it up in whatever resource you have available on Calculus of Variations.

    In this case I do not think it refers to the action integral, that is usually notated by S and the differential [itex]\delta S[/itex].
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Oh my delta!
  1. Big Oh notation help? (Replies: 2)

  2. Delta function (Replies: 1)

  3. Delta function (Replies: 3)