Bruce Yeany has an amazing YouTube channel filled with fascinating facts from the world of science. You may find lots of stuff here, for yourself or for your kids :). Those experiments visualizing 'momentum' I've found especially interesting. You may want to think about how this (i.e. 'momentum') relates to the markets.
track material is easy to work with and cheap. it is called shelf bracket tracks or shelf uprights. I have seen various hardware stores and building supply stores carry it, one company that makes it is Rubbermaid. E5 shelf upright.