Surface Tension (Soap Boat)


John J. Scavo

Richards Career Academy

5009 S. Laflin

Chicago IL  60609

(773) 535-4945




This activity is written for students of all ages.   Students will become familiar with surface tension.  Students will determine if soap will affect surface tension.  Students will determine if water temperature affects surface tension.  




Index card, any size                                                 clean water

Scissors                                                                    clean 9” pie tin or other container

Liquid soap                                                              




Fill the pie tin half full of water and have it sitting on the front table when the students come in. 

Cut a triangle out of the index card (2” high and 1” wide should do it.)  Hold it up to the students and tell them that it is a boat.

Cut a smaller triangle out of the bottom of the boat.  Tell the students that this is where the motor goes.

Place your boat in the water near the edge of the pie tin.  It will not go anywhere.  Next, remove the boat from the water.

Place a drop of the liquid detergent on you finger and touch it just inside the V notch of the boat.  Gently place the boat back in the pan of water, soapy side down, and it will jet across the surface much to the delight and amazement of all involved. 

Have the students try the process themselves.  They should have a fun time. 

Students could try different types of soaps, and both warm and cold water.  Students could try different boat styles to see which kind goes fastest.


Performance Assessment:


Students will demonstrate the ability to work scientifically and accurately in the lab.

Students will make a hypothesis as to why and how the different conditions in the water affected the surface tension.

Students should analyze error in the technique that may have affected the results.

Students will observe the reaction when soap breaks the hydrogen bonds of the water.

Students will notice a “skin” on the surface of the water, or surface tension.




- Students will have explored the possibilities of surface tension.  They will see how detergent and heat lower surface tension.  Higher level students may explore bonds and polarity affecting surface tension.




Zero to Einstein in 60 seconds, The Wild Goose Company, pp. 14-16.