Living in a world of various waves, a person constantly experiences the influence of sound. Sound vibrations are not just a phenomenon that accompanies it everywhere, but also a source of pleasure, as well as a powerful information tool. Performing a variety of functions, sound can warn of danger, give pleasure, become a means of communication. We enthusiastically listen to birdsong, pleasant music, enter into a conversation with other people.
Sound vibrations are important not only for humans, but also for animals that use sound to survive.
By its nature, sound is mechanical elastic waves that can propagate in solids, in liquids, in gases. Sound sources sound vibrations cause vibration (mechanical vibration), which is often invisible to the eye. Sound sources include physical bodies that oscillate per second (trembling or vibration) at a frequency of 16-20000 times. Sound vibrations can cause solids (string, earth crust), gaseous (air stream), liquid (sea waves).
Among the characteristics of sound, it is customary to distinguish two parameters: timbre - frequency of sound vibrations; volume - the amplitudes of the sound wave. The unit of sound volume is considered to be 1 Bel (it was named after one of the inventors of the phone - Alexander Graham Bell). Almost one Bel is not used, it is more convenient to use decibels equal to one tenth Bel. In order to have a clear idea of the dimension of volume, it should be taken into account that 10 dB is a whisper; 20-30 dB correspond to normal noise in a living room; 50 dB is a medium volume conversation; with a noise power of 80 dB, the truck engine is running; the physiological pain threshold in humans occurs at 130 dB; 180 dB can cause the eardrum to rupture.
Considering the sound vibrations of different frequencies, birds singing refers to high-frequency waves, the sound of a truck motor can be attributed to low sounds. Possessing the whole spectrum of properties and characteristics that distinguish waves of various nature, sound waves are widely used in various fields. The property of a fluid to conduct sound is actively used in the exploration of the deep sea. The well-known echo, for example, is used to determine distances in echolocation. A vivid example of natural sonar can be called bats.
A special type of sound vibrations is ultrasound, a very effective tool in the hands of physicians and other researchers. Such oscillations include waves with frequencies beyond 20,000 Hz. This type of oscillation has a number of unique properties. Passing through water, ultrasound causes it to boil (cavitation) with the occurrence of water hammer. Using ultrasound, you can tear off elements from the surface of the metal, crush solids. Ultrasound allows you to mix liquids that do not mix under normal conditions, for example, emulsions with an oil base. Ultrasound allows saponification of fats. This principle lies in the design of washing machines. The property of ultrasound to produce a crushing effect has found application in ultrasonic soldering irons.
A special type of oscillation up to 16 Hz is called infrasound. It is known that fluctuations of this frequency can have a painful effect on the human body. At frequencies of 4-8 Hz, vibration of the internal organs is felt, a frequency of 12 Hz provokes an attack of motion sickness.
Infrasound sources can be machines and mechanisms with large surfaces that undergo low-frequency mechanical vibrations (mechanical origin) or flows of liquids and gases with turbulent properties (hydrodynamic or aerodynamic origin).