capillary action

Scientific  

1. The movement of a liquid along the surface of a solid caused by the attraction of molecules of the liquid to the molecules of the solid.

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Closer Look

The paper towel industry owes its existence to capillary action, both for the way paper towels soak up liquids and for the trees out of which the towels are made. Molecules of water are naturally attracted to each other and form temporary hydrogen bonds with each other; their attraction for each other on the surface of a liquid, for example, gives rise to surface tension. But they are also attracted in a similar way to other molecules, called hydrophilic molecules, such as those in the sides of a narrow glass tube inserted into a cup of water, in the fibers of a towel, or in the cells of tree tissue known as xylem. These attractive forces can draw water upward against the force of gravity to a certain degree. However, they are not strong enough to draw water from the roots of a tree to its highest leaves. An additional, related force, referred to as transpiration pull, is required to do that. As water evaporates from the tiny pores, or stomata, of leaves, water from adjacent cells is drawn in to replace it by osmosis. Again, intermolecular attractive forces cause other water molecules to follow along, ultimately drawing water up from the roots of the tree.

Example Sentences

They function through capillary action -- the very phenomena by which a spilled liquid on the kitchen table spontaneously wicks into the paper towel used to wipe it up.

From Science Daily

Researchers used to assume these birds relied on capillary action—the tendency of a liquid to flow up a narrow tube—to take in nectar.

From Science Magazine

Fill the reservoir about every three weeks, she says, and capillary action does the rest.

From Seattle Times

The water wicks upward through the pores via capillary action, the way a droplet of blood on your fingertip is drawn into a tiny glass tube for testing.

From Seattle Times

Simultaneously, water in the soil is drawn upward by capillary action, the molecules of water sticking to the sides of very narrow pores in the ground.

From Scientific American