Soak It Up

Have you ever wondered how water gets from a tree’s roots all the way up to the leaves?

God waters every tree in the world through a process called capillary (KA-puh-leh-ree) action. Trees have a special layer of cells called xylem (ZI-lem) between the bark and the wood. Xylem carries the water up the tree. Water molecules stick to one another (a process called cohesion) and stick to other things (a process called adhesion) because one part has a positive charge and the other has a negative charge—and opposites attract. The water molecules play leapfrog up the tree as they stick to the xylem cells and to one another, until they reach the leaves at the top.

This same process happens to liquids in a straw, ink in a pen, the tiniest blood vessels in our body, and many other things. You can even spot capillary action on paper towels. Paper towels are made of small plant fibers called cellulose. When you clean up your spilled juice, the liquid gets pulled up between the paper towel fibers by capillary action.

Let’s do an experiment to see this process in action—and make something beautiful at the same time.

Let’s Do It!

Rainbow Supplies

• 5 clear glasses filled with water
• Food coloring (red, yellow, and blue)
• Paper towels

Make the Rainbow

1. Place the glasses close to one another in a row or a circle. In the first glass, add yellow food coloring to the water; in the third glass, blue; and in the fifth glass, red. Leave the second and fourth glasses of water uncolored.
2. Fold the paper towels into thirds to make strips. They should be able to reach from the bottom of one glass to the next without the middle sticking up too high. You may have to snip the ends if they are too long.
3. Insert them into the glasses, connecting each glass with the one beside it.
4. After a few minutes, you should see the colored water travel up and down the paper towels. After a while, the water will have traveled the whole length of the paper towels, coloring the uncolored water and mixing to make new colors.

Color Combinations

As the water travels from glass to glass and the colors mix, notice what new colors are created.

Extra Fun

• After the experiment, gently squeeze out the paper towels and let them dry on a baking sheet. You can use the tie-dyed towels for other crafts.