#Tinker: Soap-Powered Boat

by STEM Scouts

This experiment is all about surface tension. We tested out some similar science last fall in our “Color Changing Milk” experiment. Now, let the boat races begin!


  • Foam board, index card, or another form of heavy-weight paper
  • Liquid dish soap
  • Large bowl or dish (a pyrex dish works well, you can also use a bathtub)


  1. Cut the foam board index card into the shape of a triangle with a notch in the back. We used a heavy paper and folded it into the shape of a paper airplane. Be creative!
  2. Fill your bowl, or a sink or bathtub, with water and set your boat on the surface.
  3. Pour a few drops of dish soap in the notch at the back of the boat.
  4. For added fun, try racing your boat against a friend’s!

How It Works

According to Home Science Tools:

“Surface tension is the property that makes the surface of water appear to have a sort of elastic “skin,” and is caused by the way water molecules are more attracted to each other than to the air. When your boat sits in the water the surface tension is the same on all sides. When you put the drop of soap near the back, however, the soap molecules break the water’s surface tension. The force of the surface tension pulling on the front of the boat is now greater than the force pulling behind, so the boat moves forward. (Make sure you use clean water if you try again; it won’t work if the water is already soapy).”

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