Daily Read / Water Science
Water Science · Connect observations, mechanisms and testable explanations
How Can a Paper Towel Pull Water Upward?
Explore why water climbs through a paper towel, distinguish adhesion from cohesion, and learn what a simple observation can and cannot prove.
Device/browser voice. Pronunciation and availability vary.
Water travels even when nobody pours it
Place the bottom edge of a paper towel in a shallow cup of water. After a while, a dark wet band can spread above the water line. The towel is not a pump and nobody is pouring water onto the upper part.
The surprising question is: how can water move upward when gravity pulls things down? The answer begins with the structure of paper, not with a hidden force created by the towel.[1]
A towel is a network of fibres and spaces
Paper towels are made of many thin cellulose fibres. There are tiny spaces between the fibres. Water can enter and move through those narrow spaces.
A sheet may look solid from a distance. At a much smaller scale, its structure is closer to a network of paths. That is an example of a scientific model: we describe a structure we cannot see clearly with our eyes alone.[2]
Two attractions help the water move
Adhesion is the attraction between water and another material, such as paper fibres. Cohesion is the attraction among water molecules themselves. Both contribute to surface tension and capillary action.
In narrow gaps, those attractions can draw water upward even though gravity opposes upward motion. The rise does not continue forever: the balance of forces matters.[1]
What happens when the towel bends over a cup?
You can place one end of a paper-towel strip in a cup of water and drape the other end into a second empty cup. The first part may become wet and the moisture can travel along the strip. In a walking-water demonstration, water can eventually reach the second cup.
Capillary action helps water travel through the narrow gaps. Once the route goes downward, gravity can also help move the water. A drop of food colouring may make movement easier to see, but the colour is not the cause of capillary action.[3]
Record the evidence before making a big claim
A careful student records what was actually observed: where the wet line began, when it moved, and how far it travelled. A claim such as 'every paper towel absorbs water at the same speed' requires different evidence.
To compare two towel types, keep the strip length, width, dipping depth, cup shape and observation intervals alike. Change one chosen feature, repeat trials, and include unexpected results. This converts curiosity into a testable question.[3]
Fast lesson
Use these checks before you answer the practice questions.
A moving wet line is an observation; capillary action is the accepted physical explanation, supported by USGS and science-education sources.
There are no invented speeds or measurements here. Learners must collect their own data to rank particular towels.
Plant water transport includes transpiration and specialized tissues; this article uses paper towels only as a model of capillary behaviour.
Common mistakes
Why this fails: Food colouring highlights the water's path; it is not necessary for capillary action.
Why this fails: Adhesion is water-to-other-material attraction; cohesion is water-to-water attraction.
Why this fails: Capillary forces work against gravity up to limits set by the system.
Word Lab
Use the meaning, hear the word, then try it in your own sentence.
capillary action
nounwater movement through very narrow spaces caused partly by molecular attractions
Capillary action moved water along the towel.
fibre
nouna very thin strand making up a material
The towel contains thousands of tiny fibres.
cellulose
nouna material found in plant cell walls and paper
Many paper towels are made from cellulose fibres.
adhesion
nounattraction between different kinds of substances
Adhesion helps water cling to the paper.
cohesion
nounattraction among molecules of the same substance
Cohesion helps water molecules stay together.
gravity
nounthe force that pulls objects toward Earth
Gravity resists the water's upward movement.
observation
nounsomething directly noticed or measured
The rising wet mark was an observation.
inference
nouna reasoned explanation drawn from observations
Her inference was that small gaps helped water move.
absorb
verbto take a liquid into a material
The towel can absorb spilled water.
Check your understanding
Choose an answer, explain your choice, and then check. Hints and retries are welcome.
Try the questions here. Public practice does not save a learning record.
Core · Read and observe
Core · Read and observe practice
Find explicit facts, sequence and definitions.
1. Where is the water initially?
2. What changes when the dry towel touches water?
3. What are the small pathways in a towel?
4. What is cohesion?
5. What is adhesion?
6. Which happens first: the lower edge becomes wet or the upper part becomes wet?
Transfer · Explain the mechanism
Transfer · Explain the mechanism practice
Apply the mechanism to new observations and claims.
7. If only one edge of a dry strip touches the water, where should the wet region begin?
8. Would water rise through a completely sealed solid with no pathways in the same way?
9. A student sees blue colour move along the towel. Does the colour create capillary action?
10. What is different about adhesion and cohesion?
11. If the water continues down the far side into a second cup, what else helps?
12. Does one wet paper towel prove the fastest towel brand?
Challenge · Judge the evidence
Challenge · Judge the evidence practice
Design a fair follow-up and identify limits.
13. To compare two brands fairly, name three things to keep the same.
14. What could you measure every two minutes?
15. Two trials give different wet-front distances. What should students do?
16. Why is 'water must be moving' an inference when someone sees a wet band?
17. Why does gravity prevent a towel from drawing water upward forever?
18. Why should the report say 'in this setup'?
Practice answer key
- 1. In a cup touching the lower end of the paper towel.
Identify the starting point before explaining movement. - 2. Part of the towel becomes wet and the wet area can spread upward.
The water front is visible evidence of movement. - 3. Gaps between many tiny cellulose fibres.
Capillary action occurs in small spaces; the sheet is not a solid block. - 4. Water molecules attracting one another.
Cohesion concerns water-to-water attraction. - 5. Water molecules being attracted to paper fibres.
Adhesion concerns attraction to a different surface. - 6. The lower edge touching the cup becomes wet first.
The moving wet front spreads from the contact region. - 7. At the dipped edge.
The strip first absorbs at the water contact point. - 8. Not by the paper-towel gap mechanism described.
The explanation requires accessible small gaps. - 9. No; dye helps show the moving water.
The physical action is still the attraction and motion of water. - 10. Adhesion is attraction to another material; cohesion is water-to-water attraction.
Name the two partners in each attraction. - 11. Gravity helps movement downhill after water passes the high point.
Uphill capillary motion and downhill gravitational motion can both be present. - 12. No; speed was not compared under controlled conditions.
Claims about which towel is faster need repeated comparative evidence. - 13. Strip width and length, water depth and observation time are examples.
Only the brand or material should be intentionally varied. - 14. The distance in centimetres from the dipping point to the wet front.
A defined, repeatable measurement is stronger than 'looks wetter'. - 15. Repeat under controlled conditions and record both observations.
Differences are evidence to investigate, not grounds to delete inconvenient results. - 16. The person observes the band and reasons about water movement.
Inferences explain observations; they are not the observations themselves. - 17. Gravity resists upward motion; capillary forces have limits.
The passage does not claim unlimited lifting height. - 18. The result depends on the materials and conditions tested.
A local observation does not prove a universal claim.
Related skills
Put it in your own words
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Check your own explanation
This is self-review, not automatic marking.
Compare with a model response
The lower edge of the paper towel became wet and the wet region spread upward. Water is attracted to the cellulose fibres (adhesion), and water molecules attract each other (cohesion). Together, these attractions help water move through tiny spaces. Gravity still acts. This one observation explains the water movement in this setup, but it does not prove that every towel absorbs equally fast.
Sources and revision notes
Source check: 2026-10-10. Grade guidance is an editorial suggestion, not a standardised reading score.
- U.S. Geological Survey — Capillary Action and Water
- Science Buddies — Capillary Action Demonstration
- Ontario Science Centre — Send Water Walking
What changed in this edition?
Initial publication. Mechanism checked against USGS, Science Buddies and Ontario Science Centre. No trial measurements are claimed.