About vibrations and waves. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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Around us all the time are born in decay oscillatory phenomena. The branch "from which the bird flew off fluctuates. Clock pendulums and swings vibrate. Under the influence of the wind, trees vibrate, wires suspended on poles, water vibrates in lakes and seas.

So you threw a stone on the smooth surface of the lake, and waves ran from it (Fig. 1). What happened? The particles of water at the point of impact of the stone pressed in, displacing neighboring particles upwards, - a ring-shaped hump formed on the surface of the water. Then, at the place where the stone fell, the water particles rose like a hump, but already higher than its previous level - a second hump appeared behind the first hump, and a depression between them. Further, the water particles continue to move alternately up and down - they oscillate, dragging more and more neighboring water particles with them. Waves are formed, diverging from their place of origin in concentric circles.

Rice. 1. When a stone hits the surface of the water, waves appear on it.

I emphasize: water particles only oscillate, but do not move along with the waves. This is easy to verify by throwing a chip on the oscillating surface of the water. If there is no wind or water flow, the chip will only rise and fall above the water level, not moving with the waves.

Water waves can be large, i.e. strong, or small, weak. We call strong waves such waves that have a large range of oscillations, as they say, large amplitudes of oscillations. Weak waves have small humps - a small amplitude. The greater the amplitude of the waves that have arisen, the greater the energy they carry. The energy of the waves generated by a thrown stone is relatively small, but it can cause the reeds and grass growing in the lake to vibrate. But we know what great damage to the shore can be produced by Sea waves with large amplitudes and, consequently, high energy.

These destructions are carried out precisely by the energy that the waves continuously give off to the shore.

Waves can be frequent or rare. The smaller the distance between the crests of traveling waves, the shorter each individual wave. The greater the distance between the waves, the longer each wave. We call the length of a wave on water the distance between two adjacent running ridges or troughs. As the waves move away from the place of origin, their amplitudes gradually decrease, fade, but the wavelength remains unchanged.

Waves on the water can also be created, for example, with a stick, immersed in water and rhythmically, in time with the vibrations of the water, then lowering, then raising. And in this case, the waves will be damped. But they will exist until we stop disturbing the surface of the water.

How do swing oscillations occur? You know this very well: you just need to push them, so they will oscillate from side to side. The stronger the push, the greater the amplitude of the oscillations. Such oscillations will also be damped if they are not supported by additional shocks. We see such and many other mechanical vibrations. In nature, there are more invisible vibrations that we hear, feel in the form of sound. It is not always possible, for example, to notice the vibrations of the string of a musical instrument, but we hear how it sounds. When the wind gusts, sound is produced in the pipe. It is created by oscillatory movements of air in the pipe, which we do not see. A tuning fork, a glass, a spoon, a plate, a student's pen, a sheet of paper sound - they also oscillate.

Yes, young friend, we live in a world of sounds, because many bodies around us vibrate and sound. The sounds themselves are the result of the propagation of oscillatory movements of its particles in the air. We do not see them. How are sound waves generated in air?

Air is made up of particles invisible to the eye. With the wind, they can be carried over long distances. But they can also fluctuate. For example, if we make a sharp movement with a stick in the air, we will feel a slight gust of wind and at the same time hear a faint sound. This sound is the result of vibrations of air particles excited by vibrations of the stick.

Do this experience. Pull back a string, like a guitar, and then release it. The string will begin to tremble - oscillate around its original resting position. Sufficiently strong vibrations of the string are noticeable to the eye. Weak vibrations of the string can only be "felt" as a slight tickle if you touch it with your finger. As long as the string vibrates, we hear the sound. As soon as the string calms down, the sound will die out.

The birth of sound by an oscillating string is due to the "condensation" and "rarefaction" of air particles. Oscillating from side to side, the string pushes, as if compressing air particles in front of it, forming areas of high pressure in some of its volume, and behind, on the contrary, areas of low pressure. These are sound waves. Propagating in the air at a speed of about 340 m/s, they carry a certain amount of energy. At the moment when the area of ​​increased pressure of the sound wave reaches the ear, it presses on the eardrum, bending it inward somewhat. When the rarefied region of the sound wave reaches the ear, the tympanic membrane curves somewhat outward. The eardrum constantly vibrates in time with alternating areas of high and low air pressure. These vibrations are transmitted along the auditory nerve to the brain, and we perceive them as sound. The greater the amplitude of the waves, the more energy they carry in themselves, the louder the sound we perceive.

Sound waves, like water waves, are conventionally depicted as a wavy line - a sinusoid. The "humps" of such a curve correspond to areas of high pressure, and the "troughs" correspond to areas of low air pressure. The area of ​​high pressure and the area of ​​low pressure following it form a sound wave.

But we, in addition, live in a world of electromagnetic oscillations emitted by wires and electrical devices in which alternating current flows, a huge number of radio station antennas, atmospheric electrical discharges, the bowels of the Earth and the endless Cosmos. Only with the help of man-made instruments, electromagnetic oscillations can be detected and recorded.

Publication: N. Bolshakov, rf.atnn.ru

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