Dr. T. Ross Kelly of Boston College has a pretty cool collection of devices that he and his team of two undergraduates would like to share with you. Each device comes with a video that explains how it works. There are also links to sites that will teach you how to build these items. Science teachers from grade 3 and up will find something they can share with their classes. If you teach force and motion, check out section 5 titled Seemingly Impossible.