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Objectives

• Describe the role of surface tension in keeping water molecules together.

Materials

• Per Group:
  clean and detergent-free container of water (or sink with a plug)
  bottle of liquid detergent
  dish

• Per Pair of Students:
  a 2L milk carton (1 for every 8 boats)
  scissors
  dish soap
  eyedropper

Key Questions

• How does soap affect the water's surface tension?
• Is the boat pulled forward or pushed forward? How?

What To Do

Preparation:

1. Empty liquid detergent into the dish.
2. Cut the 2L milk carton lengthwise along the 4 long folds.

Instructions:

1. Cut out boats from the milk carton using the template provided. Optional: pre-cut the cartons before the class.
2. Cut a small notch at the back of the boat in the middle of the rear edge.
3. Place the boat near the edge of the container or sink full of water.
4. Use an eyedropper to drop a small amount of detergent in the notch at the end of the boat. The boat should move forward.

Extensions

• Try this with different kinds of liquids (i.e. milk, vinegar).
• Does the boat still move forward in different liquids?
• Try cutting out different shapes of boats. Does the shape of the boat affect its ability to move?
• Try cutting out different sizes of boats. How does the size of the boat affect its ability to move?
• Sprinkle pepper on the water before the launch so you can see the water move
• Draw a cartoon that shows the breakdown of the surface tension behind the boat and how the boat is pulled forward.

Other Resources

Science World | Boat Template PDF