Why does water soak upwards against gravity?
Water is able to soak up against the force of gravity all thanks to a little help from capillary action.
Asked by: Caroline Locke, by email
Water is wet. In scientific terms, wetting refers to the tendency of a liquid to stick to a solid. Water molecules are electrically polar, with positively charged hydrogen atoms and negatively charged oxygen atoms. This makes them stick to each other (cohesion) and to the sides of the container (adhesion). If the adhesive force is greater than the cohesive force, the molecules at the sides will try to hug the container, which causes the curved meniscus at the surface.
The force pulling the water up is called ‘capillary action’. The narrower the tube, the lighter the column of water for a given contact area with the tube and the greater the capillary action. A towel has thousands of tiny fibres that provide lots of surface area to draw the water upwards.