I've done this activity from 7th through 12th grades and it's always entertaining to see what they come up with. Since they're not actually building it, they can really think out of the box (ex- nuclear energy and thermal energy become popular). I usually do this after a lesson on energy and then I will show then the OK Go, "This Too Shall Pass" video as that is the ultimate contraption to model (in my opinion). You may also wish to show them Rube Goldberg examples. Or, modify a bit and simply u