What you need:
- Clear cups (recommend 6-7)
- Food coloring
- Paper towels
- Spoon/ something to stir with
- Time: 2 hours (can vary)
- Fill every other cup about 3/4 full of water
- Add food coloring to the water (recommend adding primary colors: red, yellow & blue)
- Stir in food coloring so it is evenly dispersed
- Fold paper towel in half longways (creating a skinnier, but still tall paper towel)
- Fold paper towel longways again, keeping height, but making it skinnier
- Place half of the paper towel into the water, and put the other half into the dry cup
- Repeat steps 4-6 until folded paper towels connect all of the cups
- Wait and watch what happens
The science and how this applies to the Earth:
Just like us, plants need water they need to survive. But, unlike humans who can just drink the water, they have roots that transfer it through the plant.
In this experiment, the paper towels will act as the roots of the plant, and the empty cups represent the leaves of the plant (which might be dry after a couple of days without rain).
You might have noticed that right away, the paper towel starts to absorb the water, much like roots absorb water from the ground.
But, this seems to defy what we know about gravity.
This is actually because of a compound found in plants and in the paper towels called cellulose. Cellulose is able to resist gravity as it pulls water up in a process called capillary action. It’s this capillary action that’s able to bring water from the ground up to the highest branches on a tree.
The water is also demonstrating properties of adhesion and cohesion.
Simply put, it’s how water sticks to itself (cohesion) or when water is sticking to something else (adhesion).
In this experiment, the water molecules attached to the cellulose as it traveled up the paper towel. This is an example of adhesion.
The water molecules are also attracted to each other, which demonstrates cohesion. We see that right away as the water bleeds up the paper towel, drawing in more water behind it.
Since the adhesion at the beginning of the experiment is stronger than cohesion, capillary action occurs and the color starts climbing up.
Once the paper towels are completely saturated, cohesion becomes stronger, gravity takes over and then the water is dropped into the empty cup.