Capillary Equilibrium Tube (Dennis Yong)
Author: Dennis Yong
Principles:Capillary Action
What is Capillary Action?
Capillary action is a property seen in some liquids. It is most pronounced in water because of water's unique properties and because water is the basis of most liquids that we see or use every day. When you use a paper towel to mop up a spilled drink or use a towel to dry yourself after a shower, you are using capillary action. When you put cut flowers in a vase of water, capillary action keeps them fresh.
To keep it simple, capillary action is the movement of a liquid through or along the surface of another material in spite of other forces, such as gravity. For instance, put a narrow straw into a glass of water. What can you observe about the level of the water in the straw as compared to in the glass? You should see that the water has climbed up the straw and is higher than the level of water in the glass. It seems to have defied gravity by moving up the straw. This is capillary action.
Standards
Plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles. HS-PS1-3
Materials needed:
-Capillary Equilibrium Tube
-Water with food coloring
Procedure
1) Mixed water w/ some food coloring to make it easier to view visually.
2). Pour the colored water into the largest tube.
3) Let the water move into the rest of the tube.
4) Pour about half-way through the big tube. At this point, you will see how the levels of each tube will vary depending on the size of the cross-section of the tube.
Explanation
The final water levels are not all the same height as one might predict. Normally water in a series of commonly connected tubes at the same height would all reach equilibrium due to equal air pressure on the columns. But in this demonstration the diameter of some of the tubes is so small that the force of capillary action pulling up on the water is greater than the air pressure above the water, thus pulling the water even higher. Since the force of capillary action is essentially constant for a particular liquid, the cross-sectional area of the tube is the determining factor for the final height of the water. The four tubes and reservoir form a single all-glass unit that is held upright in its enclosed stand.
Questions
What do you think will happen to the water level?
After the results, why are they uneven?
What forces are acting in this particular experiment?
Everyday examples of the principles illustrated
-Drawing blood at a clinic
-Liquid moving up the bristles of a brush
-Water moving up the roots of the tree.
Photos
