How does a paper towel pull water upward?
Water wets the paper's fibers and moves through the narrow spaces between them. Surface tension and interactions with those fibers produce capillary action, which can lift water against gravity.
- The scientific idea
- Capillary action
- Fields of science
- Physics
How it works
Dip the corner of a paper towel into water and the wet patch can advance above the waterline. Spaces between the fibers provide narrow passages. Water interacts with the cellulose, while attraction between water molecules helps maintain a connected liquid path.
Look closer
In a clean, narrow glass tube, water can similarly stand higher than the water around it. For comparable tubes that water wets, a narrower bore produces a greater equilibrium rise. The rise is limited: the weight of the water eventually balances the upward capillary force. Capillarity also works sideways through a sheet of paper, so the process is not simply another name for water climbing. The shape of the passage and the liquid's interaction with its walls both matter.