Surface tension results when the hydrogen in water molecules stick to one another as well as to the water below them. This creates a strong but flexible film on the water’s surface. The detergent disrupts the molecules and “breaks the tension,” making the boat go forward and the pepper move to the sides of the glass.
These simple activities demonstrate 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
- From an index card, cut out a boat like this
- Make it about 2 1/2 inches long and 1 1/2 inches wide.
- Place the boat gently on the water in the dish.
- 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.
Try this other surface tension experiment!
Use your clean pan and fill it again with water. Shake black pepper over the top of the water. Place one drop of dish soap in the middle of the dish and watch what happens!