Walking water experiment
01 // Question
How does the type of paper towel used change how fast water travels between two cups?
A testable question names one thing you change (paper towel type) and one thing you measure (time or distance).
02 // Variables
Independent
Type of paper towel- Thin, low-cost brand
- Thick, "select-a-size" brand
- Recycled paper towel
Dependent
Speed water travels between cups- Minutes until color reaches the empty cup
- Height of the water line at 30 minutes
03 // Hypothesis
IF a thicker, more absorbent paper towel is used between two cups, THEN colored water will reach the empty cup faster, BECAUSE a more absorbent towel has more small fiber gaps for capillary action to pull water through.
04 // Procedure
1. Set up the cups
Alternate full cups of colored water and empty cups in a row: full, empty, full, empty.
2. Fold the towels
Fold paper towel strips lengthwise and place one end in a full cup, the other in the neighboring empty cup.
3. Start the clock
Note the time you place the strips and check back at regular intervals.
4. Track the water line
Measure how high the water has climbed the paper towel and whether it has reached the empty cup yet.
5. Compare towel types
Repeat with a different paper towel brand and compare how long each took to fill the empty cups.
05 // Data table
| Paper towel type | 15 min | 30 min | 60 min | Time to reach empty cup |
|---|---|---|---|---|
| Thin, low-cost | ____ | ____ | ____ | ____ |
| Thick, select-a-size | ____ | ____ | ____ | ____ |
| Recycled | ____ | ____ | ____ | ____ |
06 // What to expect
Water climbs the paper towel and moves into the empty cups through capillary action — narrow gaps between the paper's fibers pull water upward against gravity, the same effect that lets a plant pull water up its stem.
Where two different colors of water share a paper towel path between them, the empty cup in the middle often turns into a secondary color, since both dyes travel into it and mix — red and blue water produce a purple middle cup.
07 // Lab notes
- Set this up somewhere it can sit undisturbed for a few hours — the cups should not be bumped while the towels are wicking water.
- Use plastic or glass cups, not paper, so the cups themselves don't absorb water and change the results.
- Food coloring can stain hands and countertops — work on a covered surface.
08 // Remember
Water climbs narrow gaps on its own. That pull is capillary action, and thicker towels have more gaps to pull through.
09 // Questions people ask
Why does water travel up a paper towel on its own?
Paper towels are made of thin cellulose fibers with narrow gaps between them. Water molecules stick to those fibers and to each other, and that combination pulls water upward against gravity through capillary action — the same process that moves water up a plant's stem.
Why does the water 'walk' from a full cup into an empty one?
Once water reaches the top of the folded paper towel by capillary action, gravity pulls it down the other side and drips into the empty cup. This continues until the water level in the two connected cups evens out.
Why do two colors mix in the middle cup?
When an empty cup sits between two different colors of water, paper towels wick both colors into it from opposite sides. Since both dyes arrive in the same cup, they mix together and produce a new color — a visible demonstration of diffusion happening after capillary action delivers the water.