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Student Guide: Investigating Surface Tension with Paper Fish

Downloadable and printable Student Guide PDF.
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Summary

What causes dew to form drops on plants, water to bead on a waxed car, and bubbles to accumulate in soapy water? The answer is surface tension. Learn more about surface tension with a pan of water, some dishwashing liquid, and a paper fish.

Useful Vocabulary

  • Molecule: The smallest unit of a compound. For example, a water molecule is the smallest unit of water.
  • Intermolecular forces: The forces of attraction (coming together) or repulsion (moving apart) that occur between a molecule and its neighbors.
  • Cohesive forces: The forces of attraction that encourage molecules of the same type to stick together.
  • Surface tension: How a liquid, like water, is held together at its surface, where the liquid and air meet. Surface tension is what enables a single drop of water to sit like a small bead on a counter top. The surface tension of water is large enough that it is difficult to make bubbles using plain water, but if you add soap to water you get lots of bubbles. This is because bubbles need just the right amount of surface tension to form; plain water has too much surface tension, and soap decreases it so that bubbles can form.

Materials

To do this activity you will need:

  • Roasting pan filled halfway with cold water (1)
  • Paper fish (1)
  • Medicine dropper filled with dishwashing liquid (1)

Directions

  1. Gently place the paper fish on the surface of the water at one side of the roasting pan. The fish shouldn't move from that spot.
  2. Place a drop of dishwashing liquid in the hole in the middle of the fish. What does the dishwashing liquid do to the surface tension of the water? What effect does this have on the paper fish?