Activity Time: 10 - 20 minutes
Recommended Grades: 3 - 8
Objectives: Explore and experiment with the surface tension of water. Then, experiment with different liquids as you aim to answer the question: Will it float?
Water is what is known as a “polar chemical.” This means that each water molecule has positive and negative charges at different ends. These molecules line themselves up so that the negative end of one molecule is next to the positive end of another. The molecules are attracted toward one another, and this creates a sort of “skin” at the surface of the water. Scientists call this “surface tension.” In nature, insects that walk on water are taking advantage of this surface tension. When you initially drop the paper clip into the bowl of water, it sinks, as the paperclip is too dense. By first laying down the tissue paper, you allow the paper clip to be lowered onto the top layer of water without breaking the “skin.” You may notice a slight depression surrounding the paper clip once it is floating. The same can be accomplished by gently lowering the paper clip onto the surface using a fork or a bent paper clip. Adding the dish soap breaks the bonds between the water molecules, thus breaking the surface tension and causing the paper clip to sink.