# How to balance a ball on a rotating plane?

I'm doing some research and I really don't want a physics engine when a simple mechanism will do. I have a ball that will be balanced on a plane. The ball will always be "stuck" to the plane and never roll off of it. The player/user will be moving this plane vertically up and down, changing its angle (rotating it some) and changing it's length. What I want is for the ball to roll along the plane as the user is interacting with the plane.

For example, player touches a surface with two fingers, touch 1 is the plane starting vector and touch 2 is the plane ending vector. The player can then move the two fingers around (increasing/decreasing the length of the plane) as well as move their fingers vertically and horizontally changing the planes position in 2d space. While doing this the ball moves along the plane with normal gravity trying to pull the ball down to the ground.

Does anyone have any idea on how to approach this? I started to think that this would be simple but then figuring in the dynamically changing length of the plane I got a bit lost.

I'll be doing this in XNA or Silverlight.