Materials
- 5 clear cups
- Water
- Food coloring: red, yellow, blue
- Paper towels
Instructions
- Arrange 5 cups in a straight line.
- Fill cups 1, 3, and 5 halfway with water. Leave cups 2 and 4 empty.
- Add food coloring:Cup 1: redCup 3: yellowCup 5: blue
- Fold paper towels into long strips.
- Place one end of a paper towel into cup 1 and the other end into cup 2.
- Place another paper towel between cups 2 and 3.
- Repeat so all neighboring cups are connected (1–2, 2–3, 3–4, 4–5).
- Wait a few hours and observe.
- The empty cups will begin to fill and colors will mix:Cup 2: red + yellow → orangeCup 4: yellow + blue → green
What’s going on?
- Paper towels are made of tiny fibers with small spaces between them. Water moves through these spaces by capillary action, which happens because water molecules stick to the paper fibers (adhesion) and to each other (cohesion).
- As the colored water travels, it drips into the empty cups. When two different colors meet in the same cup, they mix, creating new colors. This experiment shows both capillary action and color mixing at the same time.
Extension
- Place two more cups at the end of the line. Fill the new last cup with purple-colored water, and leave the cup between blue and purple empty. Connect all cups with paper towels. As the water moves, blue and purple will mix in the empty cup, creating a new blended color and extending the color pattern.
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