Heat energy, light, sound, etc. are different forms of energy. The sound is a vibration (a disturbance in space) that moves as an audible form of energy through a medium. All sound producing objects, be it a home theatre system or a music instrument, are dependent on vibrations for the production and propagation of sound.
What is a Vibration?
To understand this, let us consider a guitar. When a string of a guitar is played, it produces an audible sound. Also, after the sound is produced it is observed that the string of the instrument moves in to and fro motion. The string moves outward and reaches a maximum point and then comes back to its original position. This movement or shaking i.e. the to and fro motion of the body is termed as vibration.
These vibrations play the most crucial role in the production of sound. If these waves stop, then the sound also stops. Thus, the objects which are in vibration produce sound. The different sound waves recognized by our ears and their intensity depends upon a number of vibrations and the speed of these vibrations.
Physics of Sound:
It must be clear by now that when the strings of a guitar are played, vibrations are produced. Due to these vibrations, the medium around the vibrating body also starts vibrating. If these vibrations are produced in air, then such vibrations are known as traveling longitudinal waves.
Sound waves consist of regions of high pressure called compressions and low pressures called rarefactions. When the string starts vibrating, it pushes the air around it causing a region of high pressure near it. When the string comes back to its original position, the region around it now has low pressure. Thus, in one oscillation of the string, high and low-pressure regions are created near it. These compressions and rarefactions travel longitudinally in the medium repeatedly.
The sound moves through a medium by alternately contracting and expanding parts of the medium it is travelling through. For the propagation of sound, presence of medium is the essential condition. Owing to this reason, sound cannot travel through a vacuum because of absence of the molecules that can be compressed and expanded in space.
Suppose there is a party in your neighborhood and loud music is being played. You have your exams tomorrow. Now, what do you do? You shut the doors and windows of your room so that the intensity of sound lessens. How does the intensity reduce? Since, the energy imparted by the compressions and rarefactions keeps on decreasing, when sound travels through the medium, as energy is lost as heat and other forms. Thus, there is continuous decrease in sound energy as the distance from the source increases. By closing the doors and windows the intensity of sound is reduced due to loss of energy during propagation. We can reach to an important conclusion that sound waves require medium for their propagation. Gas, liquid or solid any medium can be taken into consideration for propagation of sound waves. The speed of sound when it is travelling through a medium depends on the type of medium. The speed of sound, travelling through air is 343 m/s or 1,235 km/h.
From the above discussion, it is evident that sound waves are an important part of the domain of Physics. It would be really helpful for students if they are able to apply what they learn by practicing with sample questions and answers like the ones provided here- NCERT solutions for sound.