I would definitely start with one *stationary* platform at the center of the screen, get that working, and once you understand that it will be easier to expand to multiple platforms.
There's code in this thread, which explains how to add images to the current view and how to move them around. How will you control the ball, by the way? Swiping the screen, or accelerometer?
http://www.iphonedevsdk.com/forum/ip...dom-rocks.html
Do not copy that code directly, but look for the method for adding imageviews and moving imageviews.
I'd make one "platform" graphic that's wider than the screen and with a hole in the center. That'll make the math easier. For now, put one platform at y=100, with the center at x= 150.
For the motion of the ball, you'll want it to fall down unless it's rolling on the platform, right? You know it's on the platform when the y value of the ball is just a little less than the y value of the platform. Then you can change to the rolling behavior.
In short, I'd break it down into getting these steps working:
1) get a ball falling down the screen
2) add the platform
3) get the ball to stop when it hits the platform
4) get the ball to roll in the right direction when it's on the platform
5) get the ball to fall through the hole (when ball center x is close to platform center x)
6) change to an array of platforms; you'll have to use a loop to check each platform.
7) change code to make platforms move up, and "push" the ball up when the ball is on a platform.
