Wednesday, July 19, 2017

classical mechanics - Integrals of Motion


Landau & Lifshitz write on the first page of chapter 2 of their Mechanics book (p.13)



The number of independent integrals of motion for a closed mechanical system with s degrees of freedom is 2s1.



Then they go on




Since the equations of motion for a closed system do not involve time explicitly, the choice of the origin of time is entirely arbitrary, and one of the arbitrary constants in the solution of the equations can always be taken as an additive constant t0 in time. Eliminating t+t0 from the 2s functions qi=qi(t+t0,C1,C2,,C2s1),˙qi=˙qi(t+t0,C1,C2,,C2s1),

we can express the 2s1 arbitrary constants C1,C2,,C2s1 as functions of q and ˙q (generalized co-ordinates and velocities) and these functions will be the integrals of the motions.



Could someone elaborate?




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