Capillary Flow Experiment (CFE) in the U.S. Laboratory/Destiny

Capillary action science experiment

Even though we usually think of water as running downhill, it can indeed flow upwards using a process called capillary action. This is the very scientific principle that explains how water goes from the soil upwards into the stem of plants. Plants contain many vein-like tubes that carry water from the plant’s roots upwards to the plant’s highest leaves via capillary action. Try this experiment to see capillary action in action.

Wrap the plastic wrap around the knitting needle and then tape the edges so that you have formed a tube. Remember, the narrower the tube, the more pronounced the capillary effect will be.
Once you have taped the plastic wrap, pull out the knitting needle. Make sure that the new plastic tube is not bent and is open at both ends.
Now pour a little of the food coloring into a glass half filled with water.
Now place your plastic tube into the glass of water.
Examine the tube carefully. The dye should climb up the tube above the level of the liquid in the glass.

Now try the same experiment with varying levels of water in the glass. Does this make a difference?

About capillary action

Capillary action is the ability of a liquid to flow in narrow spaces without the assistance of, or even against, external forces, like gravity. This phenomenon is due to the combination of cohesive forces between the liquid molecules, and adhesive forces between the liquid and a solid surface.

When a small diameter tube or porous material is inserted into a liquid, the adhesive forces between the liquid and the tube material or porous structure cause the liquid to rise up the tube or material. This happens because the adhesive forces are stronger than the cohesive forces of the liquid.

The height that the liquid rises up the tube or material is determined by several factors, including the diameter of the tube or pore size of the material, the surface tension of the liquid, and the contact angle between the liquid and the tube or material.

Capillary action is responsible for many natural phenomena, such as the ability of plants to transport water from their roots to their leaves, and the way that ink is drawn up into a fountain pen. It also plays an important role in various industrial applications, like inkjet printing and microfluidics.