Science with Shields: Episode #31 – Water Rainbow


ALTOONA, Pa. (WTAJ) — In this episode of Science with Shields, Christy Shields shows you how capillary action works by making a water rainbow.

What you need: 

  1. 7 short glasses
  2. Water
  3. Food coloring
  4. Paper Towels
  5. Scissors


First sit your seven glasses in a row. You will want to fill the 1st, 3rd, 5th, and 7th glass with water about ¾ of the way full. Basically, it should be that every other glass has water in it. Next, you want to put red food coloring in the 1st and 7th glasses. About 6 drops a glass should work. The 3rd glass fill with 6 drops of yellow and the 5th glass will get 6 drops of blue food coloring. Then, take paper towels and use the ones that give you a half size. If you do not have paper towels that can become half size, just cut the full size in half. Fold the paper towels long ways, or like a hot-dog. You’ll want to fold it again. Now, stick one end of the paper towel in the 1st glass and the other end in the 2nd. Take another folded paper towel sticking and end in the 2nd glass and the other end in the 3rd glass. Continue doing this until you reach the 7th glass. Observe how the water already starts to travel up the paper towel. Now, let your glasses sit for a few hours 2-4 hours should do the trick, and check back on them! Look how it created a rainbow and the glasses that were empty, now have water in them with secondary colors!


This experiment works thanks to capillary motion. Capillary motion or capillary action is the ability of a liquid to flow in narrow spaces without assistance. Water is fantastic at making capillary motion work because it has cohesive and adhesive properties. A cohesive property is when the same particles are attracted to each other. For example, water molecules are attracted to other water molecules. Water also has adhesive properties. An adhesive property is when different materials are attracted to each other. For example, water is “sticky” and likes to be adhesive to the molecules in a paper towel. Paper towels have capillary pores that water can move into. Water’s adhesive properties are strong enough that it can overcome its cohesive properties and also gravity to fill the pores in the paper towel and move upwards. This is how capillary action is created! Not only did we learn about capillary motion, we also learned how primary colors can make secondary colors when mixed together. Remember we only put in red, yellow, and blue food coloring into the cups. By the end, the empty glasses filled with orange, green and purple. That is because when you mix red and yellow, you get orange. When yellow and blue is mixed, it creates green. Then when you mix blue and red, it creates purple! Send us your rainbows if you try this experiment!

Check out more Science with Shields episodes on WTAJ Plus.

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