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 Quote by annamz 1. The problem statement, all variables and given/known data Essentially the problem that I am trying to solve is the same as in this topic except that it is for 3 springs and 3 masses http://www.physicsforums.com/showthread.php?t=299905 2. Relevant equations I have found similar equations as in the topic but I face a problem in describing the potential energy due to gravity for the system. The euler-lagrange equations aren't supposed to have any constants but due to the PE I find that I have constants in my euler-lagrange equations. How do you define the gravitational potential energy for a vertical two spring system? Thank you all in advance
Setting the zero of potential energy can be made wherever you want. Personally I'd set it at the top of the system. If I label the x-axis as going along with the springs and pointing downward for increasing x, the potential energy of the upper mass would be $-mgd$ where d is the distance between the top of the system and the first mass. The important thing to keep in mind is "the more you go downward, the less gravitational potential energy there is", I think.