Exploring Capillary Action
Water rises through the chromatography paper due to capillary action in this chromatograph of chlorophyll.Copyright Florian Siebeck, Wikimedia Commons http://commons.wikimedia.org/wiki/File:Chromatography_of_chlorophyll_results.jpg
Students observe multiple examples of capillary action. First they observe the shape of a glass-water meniscus and explain its shape in terms of the adhesive attraction of the water to the glass. Then they study capillary tubes and observe water climbing due to capillary action in the glass tubes. Finally, students experience a real-world application of capillary action by designing and using "capillary siphons" to filter water.
Capillary action in, part, determines the behavior of ground water in soil, which makes understanding the concept important to both civil and environmental engineers in their work to ensure the stability of buildings and roads as well as understand the environmental impact of human development. Petroleum engineers use their understanding of capillary action in the extraction of crude oil from rock reservoirs. The behavior of capillary action is exploited in blood sugar test strips to help diabetics monitor their conditions.
After this activity, students should be able to:
- Explain what a meniscus is and how it is formed.
- Describe how the combination of adhesive and cohesive forces causes water to rise in a thin tube or other confined space (capillary action).
- Design a "capillary siphon" that filters water by using capillary action to transfer water from a "cloudy" to a "clean" bucket.