Walking Rainbow
In full disclosure, this doesn’t teach a weather principle. This is a fun experiment that kids really enjoy, and it can lead to discussions about rainbows in the sky or about how water can travel up. See the end of this post for some help with those discussions! Click here to watch my demonstration. In the video I reference showing you how this unfolds. Unfortunately, my time-lapse did not record correctly, so I’ve included the picture I took at the end of the time-lapse here.
What you need:
6 clear jars
Red, yellow, and blue food coloring
Room temperature water
6 paper towels – I recommend looking for high-absorbing towels that are pre-cut into half-sheets. The smaller sheets make this experiment go a little more quickly.
What you do:
Set your jars in a circle. They shouldn’t touch, but they should be very close to each other.
Fill the 1st, 3rd, and 5th, glasses with water. Put a generous amount of red food coloring in the first, yellow in the third, and blue in the fifth. Stir each (with a separate instrument so you don’t contaminate the colors) to mix the water and coloring well. The other three glasses should be empty.
Fold all your paper towels into thirds length-wise (hot dog style). Put one end in glass one and the other in glass two, put one end of the next paper towel in glass two and the other end into glass three, etc. until you have paper towels connecting all the way around your circle.
PRO TIP: your paper towel should not stick up into the air. You really just want it to come over the lip of the jar and fold back into the next jar, so fold accordingly.
You can either stand around to watch this happen, or you can set up a camera to do a time-lapse and watch that later. The red colored water will travel up your paper towel and down into the empty glass. The yellow will do the same thing into the same empty glass where both colors will combine to make orange.
What this teaches:
There are two main lessons you can take from this: water traveling through the paper towel and colors combining to make new colors (a.k.a. the color wheel).
Capillaries in plants do this same thing! They allow water to travel up from the ground through the plant to nourish it. That’s what’s happening in your paper towels. The force in the capillaries is basically pulling the water up, counteracting the force of gravity that is trying to pull it back down toward the ground.
Parents, I’ll leave the color wheel discussion up to you. Start with the primary colors (red, yellow, blue) that we used. Show your student how red and yellow made orange. Yellow and blue did not make orange, they made green. You can use this color wheel image from usability.gov to help explain what’s happening.
The P labels Primary colors (the ones we used), S is Secondary colors (the ones we made in the empty glasses), and T labels Tertiary colors you can get by mixing a secondary color with a primary color.
