Hooked on Science: Walking water

Materials

• Three 18-ounce transparent plastic cups
• Paper towels
• Yellow and blue food coloring

Instructions

STEP 1: Fill two of the cups half of the way with water. Add yellow food coloring to one of the cups and mix. Add blue food coloring to the other cup and mix.

STEP 2: Place the three cups in a row with the empty cup in the middle.

STEP 3: Fold two paper towels into quarters lengthwise.

STEP 4: Place one end of a paper towel into the cup with yellow food coloring and the other end into the empty cup. Place one end of another paper towel into the cup with the blue food coloring and the other end into the empty cup and observe.

Explanation

Thanks to capillary action, which is the movement of water within the spaces of a porous material due to the forces of adhesion, cohesion and surface tension, the blue and yellow water moves or "walks" through the paper towel to the empty cup. As the yellow and blue colors mix in the empty cup, the color green appears. When two primary colors are mixed together, you create a secondary color. Mixing blue and red creates purple, mixing red and yellow creates orange, and mixing yellow and blue creates green.

Jason Lindsey is a science outreach educator with Hooked on Science. Check out his website, hookedonscience.org, for webcasts and experiments.