Remember ElastoLab?
A question came up on the VWNC list recently about teaching some simple physics modeling. Of course there's always EToys to look at as an example, but something else came to mind: ElastoLab, from Dave Buck:
ElastoLab is a fun program for kids that lets them play with sound, images and motion in a simulated physics environment. ElastoLab
It's a really cool simulator that lets you play with all sorts of variations on motion.