Thanks for your help,

it works like it´s supposed to. I also added:

with(Typesetting);
Settings(typesetprime = true);
Settings(typesetdot = true);

so that the returns are in the xdot notation as well.

I can also enter L with the xdot noation and not with the diff command and it still works.

The only thing that doesnt work is doing the partial derivative like this:

    (using not the partial but just d/dxdot doesnt work either)

these are working:

with(Physics);
Lxdot := diff(L, diff(x(t), t));

and:

with(Physics);
Lxdot := diff(L, xdot);              xdot meaning the xdot notation as a symbol

There seems to be difference between the diff command and the the partial "symbol" taken from the calculus pallet.

It´s not a problem though, using the diff command is just fine but still I´m curious whyit doesnt work

Thanks a lot guys