Boat Racers

INTRODUCTION

Water has very high surface tension, which results from water molecules’ strong attraction toward each other. The molecules on the surface of the water and those below them are attracted to each other so tightly that a sort of "skin" forms on the surface. It is surface tension that allows some objects that are more dense than water to float on it and insects are able to walk on water thanks to surface tension. This experiment will explore a way to break surface tension.

MATERIALS

• Index cards
• Tin foil containers
• Detergent
• Toothpick
• Water
• Ruler
• Scissors

WHAT TO DO

1. To make a boat cut out a rectangle from the index card that is 3 inches by 2 inches. The boat will be three inches long from front to back. At the end of the rectangle that will be the front of the boat cut off the corners so that the front gently curves then tapers to a point. In the middle of the back end of the boat cut a notch that is extends ½ inch into the body of the boat and is almost ½ inch wide.
2. Fill the foil pan with water.
3. Carefully place the boat on the surface of the water so that it floats. The back of the boat should be at the edge of the pan.
4. Dip the toothpick into the detergent.
5. Touch the toothpick to the water in the notch of the boat. What do you expect to happen? Can you explain what does happen?

EXTENSION

Try boat races with similar boats in the bathtub at home before any soap is added to the water.

SUMMARY

The surface tension is lower where the detergent was dropped because the detergent disrupts the water’s attractive forces. Therefore the lightweight boat is pulled across the surface of the water by the attraction of the water molecules on the surface that were not affected by the detergent.

SOURCE

"Teaching Chemistry with Toys: Activities for Grades K-9." Jerry L. Sarquis, Mickey Sarquis, John P. Williams, McGraw-Hill, ISBN 0-07-064722-4.

© S. Olesik, WOW Project, Ohio State University, 2000.