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What is capillary? How does water climb up plants against gravity?

From the book "Chemistry in Life Processes - Reactions in Action", Batia Gilad and Sara Farah, Science Teaching Center, The Hebrew University of Jerusalem

Capillarity is the ability of liquids to rise in thin tubes, apparently against gravity. The capillarity of a liquid is determined by a balance of two opposing forces: on the one hand, the forces that exist between the molecules or between the atoms in the liquid, called cohesive forces, and on the other hand, the forces created between the molecules or between the atoms of the liquid and the atoms of the material of which the surface is composed (the pipe wall the capillaries) called adhesion forces. A liquid has a high capillary capacity, when its adhesion forces are stronger than its cohesion forces.
Water has an extremely high capillary capacity. When a thin tube is inserted into water, the water rises in the tube to a certain height. Adhesion forces arise between the water and the tube resulting from the existence of hydrogen bonds between the water molecules.
and the oxygen atoms in the glass, the main component of which is SiO2.
The adhesion forces cause the edges of the water surface to stick to the walls of the tube and so to speak climb them. The surface of the water forms a concave, hemispherical shape. The cohesive forces between the water molecules and themselves cause that additional water molecules are also dragged upwards. In fact, the adhesion forces tend to increase the surface area of ​​the water and give it a concave shape, while the surface tension of the water resulting from cohesion forces tends to decrease the surface area of ​​the water and straighten the concave line while raising the surface of the liquid. The rise of the water in the tube continues until the forces of adhesion and cohesion balance with the force of gravity acting on the water and pulling it down. Unlike water, mercury has a low capillary capacity. The cohesive forces acting on mercury are higher than the adhesion forces, so the mercury will not rise up a thin tube as much as the water will.
Water does not have a high capillary capacity in tubes which are made of a material with which it cannot form hydrogen bonds. The capillarity of water has a great influence on the life of plants and animals. Water and minerals rise in the plant in the apical tubule. Xylem is one of the two tissues used to transport liquids and nutrients in vascular plants. The tip mainly transports water, salts and minerals, and is mostly composed of dead cells. The second transport tissue is the hipa, whose function is to transport organic nutrients, mainly sucrose.
The water in each stem forms a continuous column along the entire plant from the roots to the leaves at the top. The water column manages to maintain continuity thanks to adhesion forces between the water molecules and the alveolar tubule, which consists of a molecule of glucose C6H12O6.
Additional examples of capillaries: the candle wick that draws the wax up the wick as a result of low pressure in the burning area, the scent sticks dipped in the jars of perfumed liquid, and even wet toilet paper where the water will rise against the force of gravity.

5 תגובות

  1. I would like to know if the water's liquefying properties is the flow of the water? Or that flow is one feature and flow is another feature
    And does emaciation occur in the human body

  2. Beautiful and important article. Is it possible to get an answer to the question: if the capillarity principle is limited by the height of the liquid column (because at a certain point, the gravity of the liquid column is stronger than the upward pulling forces), how can trees whose height sometimes reaches tens of meters, rely on the capillarity principle and bring liquids up to the top. Are there other mechanisms?

  3. Thank you very much for explaining the following points:
    Why does adhesion cause a concave shape on the surface of the water, and basically the rise of the water in the center of the tube? After all, if there is an attractive force between the atoms of the tube and the water, then the force was supposed to act precisely on the atoms in the circumference, near the tube, and not on the center of the water far from the tube?
    What is the power of cohesion? Does the high water (raised by the adhesion in the center) pull the water in the circumference? What force is this?
    How does a drop of water on the table maintain a certain height and not spread all over it? After all, the attraction of the water molecules above is supposed to pull them down and sacrifice all the molecules to the table below as much as possible?

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