How to create a bead going along a track?

Hi, I’m trying to make a curve in Rhino of varying orders (e.g. 3rd, 5th, etc) and would like to model a sphere or bead which is fixed to the route of the curve. I would like to allow it so that I can select the bead, lift it up to a certain point along the track, and drop it so that it accelerates under gravity (there does not need to be a friction aspect). This is so I can later model the forces which are exerted on the sphere similar to how a train on a roller coaster would move along a track.

Any help with this would be greatly appreciated.