I am reading an old science experiment book and decided to use the book as a basis for some of our activities. One of the experiments that deals with surface tension is to propel a paper boat using a drop of soap and since the kids like to play with water, I thought this would be a fun thing to try.
I got DD and my Petit Monsieur together and told them we were going to try something neat. Immediately they were interested and gathered around. I had already gathered my materials: some thin cardboard, water, a tub, and some liquid soap (and a couple of small slivers of soap to try out. They didn't seem to work as well.)
I cut the cardboard into a small rectangle and cut the corners off one end so it was pointed. I also made a small notch in the back of the boat. That is where the soap will go.
DD very carefully placed the boat on the surface of the water, so it would float on top. I had her place it close to one end of the bath tub, so we could watch it move forward if the experiment worked. Next, I dropped a small drop of liquid soap into the water where the notch was in the boat and voila! The boat moved forward. I tried to get it onto video, but every time I tried, it didn't work. I will be trying again to get a video made and posted to my youtube channel.
All 3 of the kids and I were amazed. We wanted to try it again, but after a few more tries with no success, I realized that we couldn't use the same water again and emptied the tub. I filled a baby size bath tub with a few centimeters of water and tried again, this time with daddy there to watch.
The idea is this: when the soap breaks the surface of the water, the stronger pull from the water in the front pulls the boat forward.