Our next bubble experiment was Soap Power. It was was an experiment where we made a little boat, put it in some water in a bowl, and put dishwashing liquid in the engine.
The result was the boat speeding through the water for a few seconds and then stopping. If you tried it again in the same water, it would just sink. The reason it moved through the water was because the dishwashing liquid would break up the water molecules making the boat move forward. The reason it didn't work the second time was because there was already dishwashing liquid that had broken up the water.