To demonstrate Newton's third law (For every action, there is an equal and opposite reaction) I had my students design Rube Goldberg inventions. Rube Goldberg was an artist, who made a series of comics in which there were ridiculous inventions that were very complicated and only completed a simple task. On the Smartboard at work, this is one that I drew with the kids to demonstrate how theirs could work. They only had to illustrate it and write a description and not actually build it.
After using the restroom, turn on faucet(A) which will fill up sink(B). As sink fills, it will allow boat(C) to float up, lowering shampoo bottle(D). The bottle will land on toothbrush(E) and causing it to pry up toilet-paper roll(F), so that it will roll down ramp(G). When the TP hits toilet-plunger(H) it will fall down and allow the swinging shelf(I) to turn. When the shelf turns, the toothpaste(J) will drop, pulling handle(K) and flushing toilet(L). If anything goes haywire, you can always just flush the toilet manually.
