Sound is the vibrations of an object. It is transmitted in the form of waves with alternate increase and decrease in pressure. A vibrating object compresses the surrounding air molecules making them closer and then rarefies them pulling them farther apart. Also, fluctuations in the air pressure travel outward from the object and the molecules of air stays in the same average position. When sound travels it generates disturbances in the surrounding air. If your ear is within the range of vibrations, you hear the sound. When sound waves repeat irregularly noise is created but when it repeats regularly then they produce musical notes. When vibrations are fast, high note is generated and when vibrations are slow, low note is generated as shown in the below diagram for better understanding.
Characteristics of Sound
On the basis of pitch or frequency, loudness or intensity and, characteristic of sound can be recognised. Pitch is the rate of vibration of sound and is measured in Hertz (Hz). Loudness is measured in decibels (db).
Phenomena related to Sound are:
1. Diffraction: Sound waves spread like light when they move through a narrow aperture. If the aperture is small, sound waves spread out in all directions. Therefore, sound can be heard round the corner of the corridor. The Diffraction of lower frequencies in the human voice allows you to hear if someone is talking in another room or round the corner.
When Sound waves diffract they bend around obstacles or spread out through narrow opening. If the wavelength of the sound is smaller than the obstacle then almost no diffraction will takes place.
2. Reflection: Reflection of sound waves into new directions by a surface is known as ‘reflection of sound’. It follows the same laws as for reflection of light i.e. angle of incidence is equal to angle of reflection and the incident wave, normal wave and reflected wave all lie in the same plane. Do you know that sound waves can be reflected by large, hard, smooth, vertical or faraway surfaces like walls, buildings etc.
3. Refraction: It is the change of direction of a sound wave on passing from one medium to another. It is accompanied by a change in speed and wavelength of the waves. If medium is changed, speed of the wave will also be changed. For example sound waves refract when they travel over water. It does not change medium rather it travels through a medium with different properties. Thus, waves will encounter refraction and change its direction. Sound waves travel slower in cooler air than they do in warmer air. Because of this the portion of the wave front far above the water speeds ahead. Subsequently, the direction of the wave changes, refracting downwards towards the water.
4. Echo: Repetition of sound by reflection is known as echo or in other words an echo is a repeated sound because of the waves that are reflected back. Sound waves bounces off smooth, hard objects just like a rubber ball bounces off the ground. The echo sounds the same as the original sound but the direction of the sound changes. You must have tried to shout on the mountain hills, caves etc. What you noticed? When you shout loudly your voice comes back to you again and again. This is nothing but an echo only. Please note that sound are not always reflected back. If for say when sound travels and meet any soft surface then in such situation it will not come back but will be absorbed by the soft surface itself.
5. Oscillation: It is used to describe anything that vibrates. Like pendulum of a clock. Motion of a pendulum is oscillatory.
From this article we understood the various phenomena related to sound,on which principal they work. Also, what is sound, how it travels etc.are discussed.