A r c h i v e d  I n f o r m a t i o n


Have you ever tried using soap to power a boat? This simple activity works because of "surface tension."

What you'll need

1 index card
A baking dish (or sink full of water)
Liquid dish detergent
Your science journal

What to do

  1. From an index card, cut out a boat like this. Make it about 2 1/2 inches long and 1 1/2 inches wide.

  2. Place the boat gently on the water in the dish.

  3. Pour a little detergent into the notch in the end of the boat.
    What happens?
    If you repeat the experiment, wash out the baking dish carefully each time you use detergent, or your boat won't go.

Your boat should zip across the water. Water molecules are strongly attracted to each other and stick close together, especially on the surface. This creates a strong but flexible "skin" on the water's surface that we call surface tension. Adding soap disrupts the arrangement of the water molecules and breaks the skin, making the boat go forward.

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