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Science with Sean: Capillary Motion

Updated: Nov. 8, 2019 at 8:50 AM EST
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MYRTLE BEACH, SC (WMBF) - For this week's science lesson, we are showing you how water can defy gravity and move vertically.

Think of how water gets from a tree’s roots to the leaves on top, or how blood gets from your heart, up to your brain. It’s called capillary motion and we are going to demonstrate it with a paper towel and a black marker, not a permanent marker.

Step 1: Get a paper towel and draw a line with black marker

Step 2: Hang a Paper Towel over a plate so the very bottom touches the water.

Pour water in the plate so the water just touches the paper towel.
Pour water in the plate so the water just touches the paper towel.(Science with Sean)

Step 3: Watch the water rise and start interacting with the black line. This could take a few minutes. You can even set your camera phone up and create a timelapse.

Notice the difference between the black marker on the left and the permanent marker on the right.
Notice the difference between the black marker on the left and the permanent marker on the right.(Science with Sean)

Why is this happening? The answer is capillary motion.

It is defined as the movement of water within the spaces of a porous material due to the forces of adhesion, cohesion, and surface tension.

Capillary action occurs because water is sticky, thanks to the forces of cohesion (water molecules like to stay close together) and adhesion (water molecules are attracted and stick to other substances). Adhesion of water to the walls of a vessel will cause an upward force on the liquid at the edges.

The reason the black marker line started spreading apart was due to the dyes within the marker. The “Black” marker is actually made up of dyes of different colored dyes, mainly blue, magenta and yellow. You see these dyes separate in the water because the different color dyes have different weights.

You see this action every day, as this is part of the process of how trees get water from their roots to the farthest leaves at the top. You can also do another experiment to show this by dipping celery in food colored water.

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