Can water climb?
Watch capillary action in a paper towel.
One printable page with the original image and complete lesson.
Question
Why does water travel up a paper towel when only the bottom touches the water?
Answer
Capillary action allows water to move through tiny spaces, sometimes against gravity.
History
Ancient Romans used oil lamps with wicks made from materials such as linen. A wick draws liquid fuel toward the flame by capillary action, putting this principle to work long before electric lighting.
Example
Water is attracted to the towel's fibers: adhesion. Water molecules also attract one another: cohesion. These interactions, together with surface tension, help water move through the towel's tiny spaces.
Insight
Gravity still acts. The height water reaches depends on the material and its tiny spaces. Capillary action helps water move in plants, but other processes also help water reach the tops of tall trees.
Connection
The same principle helps explain absorbent materials and the movement of water through soil. Everyday objects can invite us to investigate the order and detail of God’s creation.
Challenge
Cut equal-sized strips from two types of paper towel. Fill matching cups to the same level with colored water. Dip both strips equally deep and mark the wet edges after one, three, and five minutes. Compare heights. What does your test suggest?