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Walking Water (Capillary Action)

Watch colored water "walk" from cup to cup to create a rainbow. 

What you need: 6 clear plastic cups, paper towels, water, and primary food coloring (red, yellow, blue).

Steps: 

  • Line up the cups in a straight line. Fill cups 1, 3, and 5 with water ¾ full. Leave cups 2, 4, and 6 completely empty.

  • Add red drops to cup 1, yellow drops to cup 3, and blue drops to cup 5. Stir well.

  • Fold strips of paper towel into long rectangles.

  • Put one end of a paper towel strip into cup 1 and the other end into the empty cup 2. Repeat down the line.

  • Wait 1 to 2 hours and check back to see the water fill the empty cups and mix secondary colors. 

The Science: Capillary action is the ability of a liquid to flow upward in narrow spaces—like the tiny gaps in paper towel fibers—defying gravity with the help of water molecule cohesion and adhesion.