11/11/2022 0 Comments Capillary actio![]() The movement of groundwater through the soil zone is controlled, in part, by capillary action. As more water enters the pore the capillary force is reduced to zero when the pore is saturated. As water is added to the pore, the thickness of the film increases, the capillary force is reduced in magnitude, and water molecules on the outer portion of the film may begin to flow under the influence of gravity. The adhesion of the water molecules nearest the solid material is greatest. Water entering a natural void, such as a pore within the soil, forms a film on the surface of the material surrounding the pore. The force with which water is held by capillary action varies with the quantity of water being held. However, increased density of the liquid will cause it to rise to a lesser degree. Greater surface tension and increased ratio of adhesion to cohesion also result in greater rise. The more narrow the tube, the greater the rise of the liquid. As the edges of the container are brought closer together, such as in a very narrow tube, the interaction of these phenomena causes the liquid to be drawn upward in the tube. Capillarity is the result of cohesion of water molecules and adhesion of those molecules to the solid material forming the void. The combination of the adhesive forces and the surface tension that arises from cohesion produces the characteristic upward curve in a wetting fluid. In cases where the cohesive force is greater than adhesion, the liquid is said to be nonwetting and the liquid surface will curve downward near the edge of the container. If the adhesive force between the liquid and solid is greater than the cohesive force within the liquid, the liquid is said to wet the surface and the surface of the liquid near the edge of the container will curve upward. Adhesion is the force that causes water to stick to the inside of a glass. When an attractive force exists between two unlike materials, such as a liquid and a solid container, the attractive force is known as adhesion. Cohesion produces the phenomenon known as surface tension, which may allow objects that are more dense than the liquid to be supported on the surface of the liquid without sinking. This force is responsible for holding a raindrop together as a single unit. The mutual attractive force that exists between like molecules of a particular liquid is called cohesion. A familiar example of capillary action is the tendency of a dry paper towel to absorb a liquid by drawing it into the narrow openings between the fibers. ![]() Capillary action, also known as capillarity, is a result of the intermolecular attraction within the liquid and solid materials. Play around with the camera angle to get the best contrast on the monitor.Capillary action is the tendency of a liquid to rise in narrow tubes or to be drawn into small openings such as those between grains of a rock. Comments:Īs already mentioned, it can be difficult to see the water levels in the capillaries because of the thin optical depth. Use a CCD camera with close-up lens looking as horizontally as possible the watch glass should sit on a lab jack so a suitable view can be obtained. Be generous with the ink (black, blue or red) the setup needs to be illuminated from behind with a light box, and the level in the thinnest tube is especially difficult to see. It is best to mix the ink and water before setting down the tubes. Capillary action draws the ink/water up the tubes to varying heights.Ĭlamp the tubes to a lab stand and lower them into a petri dish. The tubes, with bores 3, 2, 1 and 0.5mm respectively, are held together by tubing clamps and sat vertically in a watch glass containing ink and water (see figure 1). The setup shows the direct comparison between four capillary tubes of different bores. Due to surface tension effects water rises up a narrow bored tube the rise in height being inversely proportional to the bore's radius. ![]()
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