Diffusion vs. Capillary Action
In this familiar experiment, we are going to change the initial conditions slightly to test a hypothesis. We believe that the capillary action of water is much greater than the diffusion of dye particles within it.
Capillary Action is when water is pulled along a surface when the combination of the surface tension of the water and the cohesive forces between the water and the container pull the liquid along the surface.
We can see this easily when we make a small spill on a table. When we place a napkin just touching the spill, the water will be drawn into the napkin. This pulling force is capillary action.
Diffusion occurs when particles in a high concentration region migrate to areas of lower concentration. This is the natural tendency to eve out concentration where a path exists for material to flow.
Let's set up an experiment to test which of these forces is more powerful in water. We are not going to exhaustively prove any relationship because we are not setting up many different materials under many different condition. But this experiment should show that relatively, Capillary Action will have a greater immediate impact than the relatively slow diffusion process.
Collect the following materials:
1) 2 small to medium size glasses (use same type)
2) A slice of paper towel about an inch thick and long enough to drape between the two glasses and extend to the bottoms
3) Food dye
Capillary Action is when water is pulled along a surface when the combination of the surface tension of the water and the cohesive forces between the water and the container pull the liquid along the surface.
We can see this easily when we make a small spill on a table. When we place a napkin just touching the spill, the water will be drawn into the napkin. This pulling force is capillary action.
Diffusion occurs when particles in a high concentration region migrate to areas of lower concentration. This is the natural tendency to eve out concentration where a path exists for material to flow.
Let's set up an experiment to test which of these forces is more powerful in water. We are not going to exhaustively prove any relationship because we are not setting up many different materials under many different condition. But this experiment should show that relatively, Capillary Action will have a greater immediate impact than the relatively slow diffusion process.
Collect the following materials:
1) 2 small to medium size glasses (use same type)
2) A slice of paper towel about an inch thick and long enough to drape between the two glasses and extend to the bottoms
3) Food dye
Procedure:
1) Fill one of the glasses 2/3 with water and the other glass 1/3 with water.
2) Place 3 or 4 drops (depending on the size of your glasses you made need more) of dye into the glass that is 1/3 full.
1) Fill one of the glasses 2/3 with water and the other glass 1/3 with water.
2) Place 3 or 4 drops (depending on the size of your glasses you made need more) of dye into the glass that is 1/3 full.
3) Drape the paper towel over the glasses and extend them to the bottom.
Based on capillary action, both waters start climbing up the paper towel. As the water climbs, it draws more water into the towel like a wick draws up molten wax. What we are looking for is what happens when they meet. We expect two things to happen:
1) The capillary action will move water from the 2/3 full cup to the 1/3 full cup until the levels are equalized and there is no more presure to move water from one cup to the other.
2) We expect to see the blue dye diffuse from the 1/3 full cup (with the high concentration of dye) to the 2/3 full cup (with no dye).
The question is, which one of these movements will ocur first? Or will they happen simultaneously?
Based on capillary action, both waters start climbing up the paper towel. As the water climbs, it draws more water into the towel like a wick draws up molten wax. What we are looking for is what happens when they meet. We expect two things to happen:
1) The capillary action will move water from the 2/3 full cup to the 1/3 full cup until the levels are equalized and there is no more presure to move water from one cup to the other.
2) We expect to see the blue dye diffuse from the 1/3 full cup (with the high concentration of dye) to the 2/3 full cup (with no dye).
The question is, which one of these movements will ocur first? Or will they happen simultaneously?
What we witnessed was that the capillary action of the water moving from the 2/3 full cup to the 1/3 full cup occurred rapidly and suppressed the movement of dye from the high concentration to the low concentration. The clear water even washed down the blue that started to climb up the paper towel at the onset of the experiment.
In the above photo, you can see that the clear water has almost equalized the levels in the cup. Even with this much slower pressure moving the water, there is still no indication that the blue is able to fight this small flow of water.
In the above photo, you can see that the clear water has almost equalized the levels in the cup. Even with this much slower pressure moving the water, there is still no indication that the blue is able to fight this small flow of water.
After the levels in the cup were equalized, the blue dye started to make it's way to the other side. After a while, the clear water began to become colored blue as the dye diffused through the water in the paper towel to the area of low dye concentration.
Based on this simple observation, we can see that the flow of water between the cups due to capillary action was stronger than the diffusion rate of the dye between the cups.
If you were performing this as a science fair experiment, you would want to run multiple trials with different dyes, at different temperatures, and different wicking materials (paper, cloth, etc) and you would want to know the times that you reached the different milestones like when the water was equalized, when the dye reached the crossover between the two cups, and when the two cups were at the same color.
We hope you enjoyed this experiment and it has motivated you to learn more about these processes.
If you were performing this as a science fair experiment, you would want to run multiple trials with different dyes, at different temperatures, and different wicking materials (paper, cloth, etc) and you would want to know the times that you reached the different milestones like when the water was equalized, when the dye reached the crossover between the two cups, and when the two cups were at the same color.
We hope you enjoyed this experiment and it has motivated you to learn more about these processes.