I think 2D will be enough.

The experiment is the one you can see on this movie
[url=http://www.physique-appliquee.net/videos/mecanique/deviation_bille.mov]http://www.physique-appliquee.net/videos/mecanique/deviation_bille.mov[/url]

So, moving trajectory in fixed direction.
The speed of the marble can be changed.
The place where we put the magnet can be changed as well.

Is it better described like this or do you need any other details ?

Regards,