One of the senses used by man is hearing. The whole world around us is filled with sounds of various kinds, some of which we are able to perceive. Where do sounds come from?Sound is a series of compression and rarefaction waves that can travel over great distances. It is produced by the vibration of the particles present in the material through which the sound “travels”. The presence of some medium is essential for sound waves to travel, that is, sound cannot propagate in a vacuum.
There are various types of media through which sound waves can travel: solids, liquids, gases, plasmas and so on.
The speed and physical characteristics of sound depend to a considerable degree on the conditions of the environment. The frequency of sound is nothing other than the total number of wave oscillations produced. The length of sound waves varies with frequency. Our ears are able to hear only those sound waves that lie in the range from 20 to 20000 oscillations per second.
In principle, there are three things that are necessary for the transmission of sound:
- a source that can create sound;
- a medium through which sound can pass (water, air and so on);
- a receiver or detector that receives the sound.
When a physical object moves in air, it causes a vibration, which leads to the formation of a series of compression waves in the air. These waves propagate in the form of sound. For example, when musicians play the guitar they set the strings into oscillatory motion. The motions of the strings, in turn, create sound compression waves in the surrounding air. Our vocal cords, which create sound by vibrating, are another example. The movement of a train along rails, through which sound vibrations are transmitted, may serve as an example of the transmission of sound through solids.
At room temperature, sound travels through air at a speed of 343 m/s, through water at 1482 m/s, and through steel at 5960 m/s. Sound waves in a gaseous medium have a relatively slow speed, because its molecules are weakly bound and have to cover a large distance to collide with another molecule. In a solid medium the atoms are packed so closely that vibration is easily transmitted between neighbouring atoms, and sound travels fairly fast.
Sound waves, on reaching a receiver, cause some vibration in it. Thus, when sound waves reach our ears, the eardrum, located inside the ear, vibrates. This vibration reaches the inner ear and the auditory nerves. After the auditory nerve takes up these vibrations, electrical signals are transmitted to the brain, where the oscillations are recognised as sound. As a result, we can hear sounds. A device such as a microphone can detect sound. Sound waves create vibrations in a membrane, which brings about a change in electrical signals, which can be amplified, recorded and so on.
It is hard to imagine the modern world without the whole variety of music, films, telephone communication and so on. All this would not be possible without the study of the nature of the creation, transmission and reception of sounds.