III.Capillary+tubes

IMPORTANT NOTE*
 * The rest of this page will be much easier to understand if you first read the links to *adhesion and cohesion* and *surface tension*

__WHAT IS CAPILLARY ACTION??__ Capillarity or capillary action- phenomenon in which the surface of a liquid is observed to be elevated or depressed where it comes into contact with a solid. For example, the surface of water in a clean drinking glass is seen to be slightly higher at the edges, where it contacts the glass, than in the middle.**
 * we saw this in class when in the water experiments, we observed water rise up small tubesfar past the water mark in the glass we had put it in

__WHY DOES THIS HAPPEN???__ Remember two important things about water: 1. it "wants" to stay together, its molecules are attracted to each other- this is called cohesion, it is the cause of surface tension 2. It is also attracted to other molecules- this is called adhesion

When a tube is placed into the water, the water climbs up the tube. This is because the water molecules are attracted to the molecules of the tube: adhesion

The reason the water does not just climb up the sides of the tube, but the entire level rises is due to COHESION. The water molecules "want" to stay together, so as the molecules move up the sides of the tube, they drag the molecules along with them.

Another way to look at it: Capillary action is the result of [|adhesion] and [|surface tension]. Adhesion of water to the walls of a vessel will cause an upward force on the liquid at the edges and result in a meniscus which turns upward. The surface tension acts to hold the surface intact, so instead of just the edges moving upward, the whole liquid surface is dragged upward.