thank you for the link and the basics, this could help.
RigidBody is a
Sphere, and doesn't rest on my moving
KinematicBody. I have to glue it to the KinematicBody somehow, I think the best way is to copy velocities from the
KinematicBody to the
RigidBody, but KinematicBody has no velocity properties.
P.S.: Yes, the Sphere should use real life physics, but not on moving platforms.