is a form of energy that causes the sensation of hearing. It is produced because of vibrations. A vibration is defined as a rapid to and fro or back and forth motion about a mean position. Sound is a vibration that can be heard. Sound can be produced from almost all the objects around us. The vibrations of a body while producing sound may not always be clearly visible to the human eye.
In humans, sound is produced by the voice box or the larynx, which is present in the upper portion of the wind pipe of the throat. Two vocal cords are stretched across the voice box or larynx in such a way that it leaves a narrow slit between them for the passage of air. When air is forced by the lungs through the slit, the vocal cords vibrate, producing sound. Muscles attached to the vocal cords can make the cords tight or loose. When the vocal cords are tight and thin, the type of voice is different from that when they are loose and thick. The vocal cords in men are about 20 mm long, in women about 15 mm long; children have very short vocal cords.
We hear sound with our ears
. The ear drum
has a vibrating membrane like a stretched rubber sheet. When a sound note reaches the ear, the ear drum vibrates, and the vibrations get converted into electrical impulses that are carried to the brain via the auditory nerve. This gives the sensation of hearing.
Sound travels as a wave. It needs a material medium to travel. Sound travels through gases, liquids and solids. The speed of sound is the maximum in solids, less in liquids and the least in gases. Sound cannot travel through vacuum.
To produce pleasant sounds
, a number of musical instruments have been developed. Percussion instruments produce sound due to the vibration of membranes, e.g. tabla, cymbals, ghatam, kartal and manjira, stringed instruments due to the vibration of strings, e.g. sitar, veena, violin, guitar and ektara, and wind instruments produce sound due to the vibration of an air column, e.g. flute and the trumpet.