Explore how plants and trees get water from their roots to their highest leaves through this fun water transport activity!
- Clear cups (3)
- Food coloring or liquid watercolors
- Paper towels
- Scrap paper
- Select two colors to use for this activity. Selecting two primary colors — red, blue or yellow — will produce the most dramatic results.
- Fill two clear cups halfway with water.
- Put a few drops of your first color into one cup and a few drops of your second color into the second cup. Stir to mix.
- Set an empty clear cup in between the cups with colored water.
- Brainstorm how you might be able to get the two colors to mix without pouring the water from any of the cups. Write your ideas down on a piece of paper.
- Roll a piece of paper towel lengthwise. Place one end of the rolled paper towel in one cup of colored water to create a thick bridge for the water to travel into the empty cup.
- Repeat with the other cup of colored water. The paper towel bridges do not need to touch, but it is fine if they do.
- Watch as the paper towels start to spread the colored water along the bridge. Write down or draw some observations on how the water is traveling.
- Make a hypothesis about what color you think the water in the empty cup will be and make note of it on a piece of paper.
- It will take a while for the water to travel all the way up the paper towels and into the empty cup. Take a break and check to see if any leaves in your neighborhood have started to change, then check back on your activity later.
- To speed up the process, dip approximately three-quarters of each paper towel bridge into the cups of colored water to saturate them.
What Are We Discovering?
The movement of the water from a cup, up through a rolled paper towel bridge, to another empty cup is called capillary action.
Water has both adhesive and cohesive properties. When you wet a paper towel, some of the water sticks to the paper towel. This force is called adhesion. The water molecules that do not adhere to the paper towel stick to other water molecules. When water sticks to itself, it is called cohesion. Adhesive and cohesive forces work together to pull the water up the paper towel against the force of gravity, demonstrating capillary action.
In plants and trees, capillary action is what allows water to be pulled from the ground all the way up to the highest leaf.
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