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The interaction between contacting surfaces of a liquid and a solid that distorts the liquid surface from a planar shape and causes the liquid to rise or fall in a narrow tube.
The movement of a liquid along the surface of a solid caused by the greater attraction of the liquid's molecules to the surface of the solid than to each other. The liquid's molecules adhere to the solid surface and also to each other, so that each molecule pulls the next one along. Water moves through the roots of trees or into the pores of a sponge or towel by capillary action.
Did You Know? The paper towel industry owes its existence to capillary action. Towels easily draw up water, much as a drop of blood to be taken for a test will defy gravity and travel up a small tube. In both cases, the force of gravity is still in effect, but it is being overwhelmed by the stickiness of liquids. The molecules of liquid stick to the sides of a narrow tube or the tiny channels in a towel, and other molecules stick to the first molecules, so the liquid crawls upwards. Some people think that this capillary action is responsible for moving water from the roots to the highest leaves of a tree, but it can only push water up so high. The remaining trip is powered by transpiration pull. As water evaporates from leaves, it sets up a suction that turns the entire tree into a straw through which the water on the bottom is pulled up.