Learn what capillary action is and how this relates to plants and rainbows.  Grab some common household items and get the kids involved. They will soon begin to understand how the movement of water within the spaces of a porous material is helpful to plant life

Observe both capillary action and color-mixing with this experiment.

Materials:

jars (3 or more – an odd number)
water
food coloring (two or more primary colors – red, yellow, or blue)
paper towels
scissors

Procedure:

1. Fill every other jar with water colored by different colors of food coloring.
2. Fold the paper towels in quarters and cut the ends.
3. Place one end of each paper towel in a full glass of water and one end in an empty glass.
4. Make predictions, then observe what happens.  Do you think the empty jars will stay empty?  If not, what color water do you expect to see in them?

How it Works:

Capillary action is the movement of water within the spaces of a porous material, the paper towel in this case.  Water molecules bind to the paper towel through a process called adhesion, but the water molecules also stay close to each other because they are cohesive.  The result is that water is drawn up through gaps in the paper towel, which act as capillary tubes.  Another example of this process is where water travels from the roots of a plant to the leaves.  In this experiment, water should be drawn through the paper towels from the full jars to the empty jar/s.  And if you’ve used different colors of water, those colors should combine in the jar that was initially empty, creating a new color.  With seven jars and three primary colors, you could approximate a rainbow.

Sources:
Coffee and Crayons
Science Sparks
WhizKidsScience
USGS

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