Walking Water!

Key Concepts

Materials: 
7                     Cups
6                     Paper towels
4 cups          Water 
4 colors*     Food Coloring (recommended: red, yellow, blue, purple)

Note: If you only have 3 colors, then you can use 5 cups, 4 paper towels, and 3 cups of water. If you only have 2 colors, then you can use 3 cups, 2 paper towels, and 2 cups of water. 

Activity Directions:
  1. Arrange the cups in a row.
  2. Pour a cup of water into every other cup, starting with the first cup. There should be an empty cup in between each cup with water.
  3. Add five drops of food coloring in each cup that contains water.
  4. Fold each paper towel in half with the crease parallel with the longer side of the paper towel (hot dog style). It should now be the same length but half as wide. 
  5. Fold each paper towel once again in the same fashion. It should now be the same length but one fourth as wide. 
  6. Now, fold each paper towel in half with the crease parallel with the shorter side of the paper towel (hamburger style). It should now be half as long and just as wide as in step 5.
  7. With each pair of neighboring cups, place one end of the paper towel inside one cup and the other end in the other cup, so that the paper towel touches the bottom of both cups. 
  8. Leave the cups to sit for 24 hours, and observe!

Discussion Questions & Science Explanations:
  1. How does water move up the paper towels if gravity pulls things down?
    1. Water moves up the paper towels in a phenomenon known as capillary action. 
  2. What is capillary action?
    1. Capillary action is the combined forces of the cohesion between water molecules and the adhesion between water molecules and the paper towel. 
  3. What is cohesion and adhesion?
    1. Water molecules attract each other because of the intermolecular forces between each particle. Think of the water molecules as best friends who want to stick together. 
    2. Cohesion occurs when water molecules stick to each other because of the attraction between them, and adhesion occurs when the water molecules are attracted to other substances, like the paper towel. 
    3. Because the water molecules are attracted to each other, when the fibers in the paper towel pull the water molecules through the paper, the other water molecules are pulled as well. This leads to water as a whole traveling through the paper towel.

Additional Experimentation:
  1. Try arranging the cups in a circle instead of a line. Does the water still travel across the paper towels then? 
  2. Try using even more colors and even more cups! ​
Suggested video: https://www.youtube.com/watch?v=hGwG--GZEfw

​Published 7.31.2020

Author: Alex Zhang