This addictive program can easily keep you busy for rest of the weekend so be careful :). Phun is a physics simulator that even kids can use and its absolutely a delight. I watched the video and had to immediately download to give it a try. At first the interface might seem not as easy but after reading tutorial in main page and forums, you might be able to accomplish everything shown in video in less than 15 min of learning curve! Simply the easiest, powerful and most fun physics program I’ve come across.