# Independent variables of the Lagrangian

1. May 6, 2014

### JanEnClaesen

Why are y and y' treated as independent variables, while they are not?

Another slightly related question:
if ' = d/dt then df'/dg' = df/dg because f' = df/dg g', but if we differentiate f' to g' we implicitly assume that df/dg is independent of g', is it?

2. May 6, 2014

### JanEnClaesen

Perhaps because y and y' are the values of y and y' at the boundaries of a path, in which case they do seem independent.
Hence a natural follow-up question, instead of binding the positions, why don't we bind the velocities?

3. May 6, 2014