I am doing a rubber band powered boat for a project, but I'm not too sure as to what physics theory I can incorporate into it. We made a small wood board boat and powered in using rubber bands and tested to see how long it took to reach the end of the bath tub. Every time we added one more rubber band and saw that when we added the 8th rubber band, the boat started to sink. When we added the 10th rubber band, the boat flipped over. How do I know the energy in joules? I would really appreciate your help.