Re: What is the difference between capillarity and adhesion and cohesion

Basic definitions
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Attractive forces between molecules of the same type are called cohesive forces.

Attractive forces between molecules of different types are called adhesive forces.

Surface tension is a contractive tendency of the surface of a liquid that allows it to resist an external force.

Capillary action, or capillarity, is the ability of a liquid to flow in narrow spaces without the assistance of, and in opposition to, external forces such as gravity.

An example using water and a straw
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Capillary action however, is related to the adhesive properties of water. You can visualize capillary action by placing a straw into a glass of water. The water 'climbs' up the straw. What is happening is that the water molecules are attracted to the straw molecules. When one water molecule moves closer to the straw molecules the other water molecules (which are cohesively attracted to that water molecule) also move up into the straw. Capillary action is limited by gravity and the size of the straw. The thinner the straw or tube the higher up capillary action will pull the water up into the straw.

See a more detailed description at the UC Davis ChemWiki: http://chemwiki.uc davis.edu/Physical_Chemistry/Physical_Properties_of_Matter/Atomic_and_Molecular_Properties/Intermolec ular_Forces/Cohesive_And_Adhesive_Forces/Capillary_Action