Thank you for your answer!

I found sth. in the internet:

http://www.spiralwishingwells.com/guide/physics.html
The form of a funnel is -1/x^2.

But it doesnt help me.

I dont know the lagrangian but i know the other moments... but i dont have any approach / idea how to start with my calculation. Can anyone help me there pls. is it that complicated?

has anyone a equation which i could use to start?