1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Virtual displacement

  1. Aug 21, 2014 #1
    While deriving lagrangian equation using D'Alembert's principle, in Goldstien, they defined a variable called "virtual displacement". Why do we need a concept called virtual displacement? What is its signigicance in classical physics?
  2. jcsd
  3. Aug 24, 2014 #2

    You can read in wikipedia about it:


    I am not an expert on this matter but from what I have seen, virtual displacements are small spatial displacements [itex]r_{i}[/itex] (with no time displacement) over the path of motion and are used in Lagrangian mechanics.

    The least action principle is part of Lagrangian mechanics and states that particles follow a path whose action is stationary, which means that any "small" virtual displacements does not change the action.

    You can also read about the least action principle in wikipedia:


    Best regards,
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook