What is capillary action?
Capillary action is when water sticks to the walls of something and moves upward, defying gravity. One example of this is how water moves upward through a plant, from the roots to the stem to the leaves.
What are the factors affecting capillary action?
Diameter of the straw/tube - Smaller diameter tubes have more surface area, so it allows capillary action to pull up water higher than in large diameter tubes.
Cohesion - Cohesion is attraction between molecules of the same substance. Capillary action is more likely if the cohesive forces aren’t that strong.
Adhesion - Adhesion is attraction between molecules of different substances. Capillary action is more likely if the adhesion forces are strong.
Surface tension of the liquid - Less surface tension increases capillary action (because less surface tension means that intermolecular forces are decreased, which decreases cohesive forces).
Density of the liquid - A denser liquid will rise to a lower height in a capillary tube.
Temperature - As the temperature increases, the density increases, so the liquid will rise to a lower height.
What are the applications of capillary action?
- How to make pens (capillary action makes the ink rise)
- How plants work (capillary action makes the water rise)
- How to make a candle wick (capillary action makes the water rise)
- How to decide the diameter of a straw (capillary action makes the fluid rise to your mouth, so the tube needs to be small enough to let capillary action happen)
- Donating blood (capillary action takes place as the nurse places a small tube, called the capillary tube, into the bloodstream. Because the tube is so thin, the bond between the blood molecules is stronger than the force of gravity, therefore rising up the small tube!)
Hope this helps!