Link: Physion - Physics Simulation Software

Physion is a free physics simulation software that helps you to create various physics simulations in 2D. You can create physical objects like gears, polygons, circles or pulleys, springs etc. that obey the laws of Physics and do experiment with it. You can create almost any object or draw any object in 2D and do experiments in the way you want with it.
I can't see the demo videos on the website [blocked by our ISP] However I have downloaded the program and set it up on a single computer. Setup installs 28 scenarios with 'things going on' in them. These can be edited or you can create and save your own. I think that with a little practise this could prove quite useful as a teaching aid.

Catapult scenario running:

Note: I installed it on my workstation and the program disagreed with my nVIDIEA card. It said that I should update the driver but it is the latest driver?