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Water Drop Races

In this activity, students explore the ideas of surface tension and absorption by manipulating water drops on waxed paper, and comparing the results to regular paper.

Water and wax do not get along. Waxed paper pushes water away and does not absorb it.  

The surface tension of the water pulls it into a little round blob; these blobs, or drops, can slide around waxed paper because the paper does not absorb it.

Water "prefers" to stick to itself (adhesion) more than it sticks to other substances (cohesion). 

Wet and Dry Printable guide.

These activities are part of Science World's Big Science For Little Hands program. They were developed and tested with preschool and kindergarten educators.

Objectives

  • Explore the behaviour of water on different absorptive materials.

Materials

  • Per Child:
    1 pipette or small sponge
    1 piece of waxed paper, about 15 cm x 15 cm
    1 piece of smaller regular paper
    1 straw

Key Questions

  • Does the regular paper get wet? What about the waxed paper?
  • Which paper absorbed the water? Which one did not absorb the water?
  • Where else do you see water drops like this?

What To Do

  1. Drip a drop of water onto the piece of regular paper using a small wet sponge or a pipette. Observe what happens.
  2. Drip a drop of water onto the piece of waxed paper. Observe what happens.
  3. On the piece of paper that did not absorb the water, move the water drop around by blowing at it through a straw. You can also try carefully tilting the paper to “race” your water drop.
  4. Try making smaller drops. See if you can race them by tilting your paper. Then, can you bring the drops back together into one big drop?

Extensions

  • Draw a wiggly path or a target on a piece of paper. Put it under the waxed paper and try to blow the water drop along the path or onto the target.
  • Exchange the waxed paper for plastic wrap or a clear plastic lid (or a similar material). How does this change what happens?
  • Experiment with blowing the drops together, then apart. Are you able to?
  • Add a few drops of food colouring in addition to the water drops! Does this change what happens? HINT: if you leave this coloured water to dry, you have an art piece.