You can produce slower vibration in a simple pendulum. It consists simply of a weight hanging by a thread. When the ball is given a small push, it performs to and fro movements which you can easily observe. These slow vibrations are also known as oscillations.
The important characteristics of vibrations are its frequency, amplitude and time period. These determine the characteristics of the sound produced.
The maximum extent of vibration of the vibrating body from its mean position is known as its amplitude.
The time taken by the vibrating body for one complete vibration is known as the time period of vibration. It is denoted by T.
T=1/f and f=1/T
Time period and frequency are reciprocals of each other.
Sound can be characterized by the loudness, pitch and quality.
The quality of a sound is that property by virtue of which two sounds of the same pitch and loudness produced by the two different musical instrument or people can be distinguished.
The speed of sound changes with the change in medium. Speed also depends on the physical state and temperature of the medium. At higher temperature, the speed of sound is higher, while at lower temperature, the speed decreases.
The speed of sound is maximum in solids (5920m/s in steel), lesser in liquids (1480m/s in water) and minimum in gases (330m/s in air).
Sound travels in the form of waves of vibrating air molecules. When these waves reach our ears we hear the sound.
The ear has three parts: Outer ear, Middle ear and Inner ear.
It consists of the pinna, ear canal, and the eardrum or the tympanum. The pinna gathers the sound waves and then leads to the ear canal from where they strike the eardrum.
The vibrations from the eardrum are transmitted to three closely-packed bones called the hammer, anvil and stirrup. These three bones finally transmit the vibrations to the inner ear.
This consists of cochlea, which is a long coiled tube. It contains a fluid and has numerous cells with hair. These sensitive hair cells transmit the vibrations to the brain through the auditory nerve, for the brain to register the sound.
Sound heard after reflection from a surface is called echo.
Just like heat or light, when sound falls on a surface, it is partly reflected and partly absorbed.
Soft surfaces are better absorbers of sound whereas hard surfaces are better reflectors of sound.
Sounds can be classified as musical sounds and noise.
The sounds produced by a tuning fork, violin, veena, flute and piano are pleasing to the ear. They are called musical sounds. They are produced by regular, periodic vibrations.
Certain sounds such as thunder, the rattling of wheels on a rough road, or a large number of people talking at the same time inside a room are unpleasant to hear. These sounds are called noise and produced by irregular and non-periodic vibrations.
Musical instruments are categorized into three types:
Stringed instruments, wind instruments and percussion instruments.
Stringed instruments make use of a string or wire to produce vibrations and sound. The frequency of sound is varied by varying the length of the vibrating wire.
In a sitar, the shorter the length of the wire, the higher the pitch it produces.
Wind instruments use the principle of a vibrating air column to produce sound. The frequency is varied by changing the length of the vibrating air column.
Flute, shehnai and clarinet are some well known wind instruments.
They are instruments in which vibrations of a stretched animal hide produce sound. The frequency of vibration can be increased by stretching the hide more.
Table, drums and mrindangam are some examples of percussion instruments.
Too much noise in our surroundings is known as noise pollution.
The loudness of sound is measured in decibels (dB).
The sources of noise pollution include road traffic, jet planes, trains, construction sites, factories, uses of loudspeakers, lighting of crackers during festivals, and noise from radio and television.