Step-by-step tutorial
Step 1
Gather your materials.
Step 2
Cut a few ½-inch wide strips from a piece of paper towel. Then, cut each strip in half lengthwise (aka hotdog style).
Step 3
Place five cups about one inch apart from each other. Then, lay a small strip in between each of them.
Step 4
Squeeze two drops of red food coloring into the cup on the far left, two drops of yellow food coloring into the cup in the middle, and two drops of blue food coloring into the cup on the far right. Leave the other two cups empty!
Step 5
Pour water into each of the cups with food coloring, filling almost to the top.
Step 6
Place one end of the paper towel into one color, and the other end into another. Watch what happens!
Learn more
The color climbs up the paper towel bridges thanks to one nifty property of water — it likes to stick to things. (That’s why your finger gets wet when you dip it in water. The water molecules stick to you!)
When water gets into a tiny space — like between paper fibers — it’ll stick to the sides of the fibers. Because it also sticks to other water molecules, more water gets pulled into the space after it. Gradually, by pulling in more water and sticking to the sides, the water will inch its way along and climb all the way up the paper. This process is called capillary action, and it’s also how water gets all the way from a tree’s roots up to the topmost leaves!