Classroom sets for teaching mechanical principles. Popout-n-paste paper models help students see how simple mechanical principles work. Students build a clever paper model that makes a bird peck by turning a crank. In doing so, they will experience first hand the mechanics of cams at work.   Cams make rotary motion (the turning of a crank) into reciprocating motion (back and forth or up and down),   They are used in all sorts of machinery. The most well known of which is, of course, the engine of an automobile.   A fun and wonderful design and technology project.