January 2016

Sailing on Surface Tension (1/6/16)

MATERIALS:

  • Scissors
  • Cardboard/Thick paper
  • Water
  • Cake pan or large clear bowl
  • Liquid Detergent
  • Toothpick or Q-tip

INSTRUCTIONS:

  1. Cut out a small boat shape from the cardboard. (Feel free to experiment with different shapes to send across the water – a cutout fish will work as well)!
  2. Using the scissors, make a small notch in the cardboard at the back of your vessel of choice.
  3. Fill up the cake pan or bowl with water, and gently place your boat on the water so it floats.
  4. Gently dip your Q-tip or toothpick into the detergent, allowing a generous amount to cover the tip.
  5. Stick your Q-tip into the water right behind the notch in your boat.
  6. Watch your boat take sail! The detergent should break the surface tension and allow your boat to shoot across the water. Continue touching the water with the Q-tip to continue powering your boat. Experiment with other liquids besides the detergent to see what others will break surface tension and send your boat or fish flying across the pond!

HOW DOES IT WORK?

Planet-Science.com describes our experiment best: Water molecules are strongly attracted to each other and stick close together. This creates a strong but flexible “skin” on the water’s surface called surface tension. Surface tension allows the cardboard boat to float on top of the water.

Adding soap disrupts the arrangement of the water molecules. The water molecules near the detergent are attracted to the detergent as well as to other water molecules, so the surface tension of the water behind the boat decreases. Water molecules move from areas of low surface tension to areas of high surface tension. The boat is pulled towards areas of high surface tension by the water in front of the boat. Experiment with different shapes and liquids to set sail on your pond. That’s surface tension, folks!