If you like to drink cocktails or other drinks from a straw, you have probably noticed that when one of its ends is lowered into a liquid, the level of the drink in it is slightly higher than in a cup or glass. Why it happens? Usually people don’t think about it. But physicists have managed to study these phenomena well for a long time and even gave them their own name - capillary phenomena. Our turn came to find out why this happens and how this phenomenon is explained.
Why do capillary events occur?
In nature, everything that happens is a reasonable explanation. If the liquid is wetting (for example, water in a plastic tube), it will rise up the tube, and if it is non-wetting (for example, mercury in a glass cone), then it will drop. Moreover, the smaller the radius of such a capillary, the higher the liquid rises or falls. What explains such capillary phenomena? Physics says that they occur as a result of surface tension forces. If you look closely at the surface layer of liquid in the capillary, you can see that in its shape it represents a certain circle. Along its boundary, the force of the so-called surface tension exerts pressure on the walls of the tube. Moreover, for a wetting liquid, the vector of its direction is turned down, and for a non-wetting liquid, up.
According
to Newton’s third
law, it inevitably causes counter-pressure equal in magnitude to it. Just it makes the liquid rise and fall in a narrow tube. This explains all kinds of capillary phenomena. However, most likely many have already had a legitimate question: “And when will the raising or lowering of the liquid stop?” This will happen when the force of gravity, or the force of Archimedes, will balance the force that causes the fluid to move through the tube.
How can capillary phenomena be used?
Almost every student or pupil is familiar with one of the applications of this phenomenon, which has become widespread in the production of stationery. You probably already guessed that we are talking about a capillary handle.
Its device allows you to write in almost any position, and a thin and clear mark on paper has long made this subject very popular among the writing fraternity.
Capillary phenomena are also widely used in agriculture to regulate movement and preserve moisture in the soil. As you know, the land where crops are grown has a loose structure in which there are narrow gaps between its individual particles. In fact, it is nothing but capillaries. According to them, water enters the root system and provides the plants with the necessary moisture and useful salts. However, along these paths, soil water also rises and evaporates quickly enough. To prevent this process, capillaries should be destroyed. Just for this, they carry out loosening of the soil. And sometimes the opposite situation arises when it is necessary to strengthen the movement of water through the capillaries. In this case, the soil is rolled away, and due to this, the number of narrow channels increases. In everyday life, capillary phenomena are used in a variety of circumstances. The use of blotting paper, towels and napkins, the use of wicks in
kerosene lamps and in technology - all this is possible due to the presence of narrow long channels in their composition.