Sound

By christo vinodVIII C

sound What is sound ?sound  is a  vibration  that propagates as a typically audible  mechanical wave of  pressure  and  displacement, through a  medium such as  air  or  water. In  physiology  and  psychology , sound is the  reception  of such waves and their  perception  by the brain.

activityAn activity to prove that sound is produced due to vibration produced in a medium .

Take a plastic ruler {15cm} . Place the ruler on the table top such that 6 cm of the ruler projects out from the edge of the table . Place a brick on the ruler . Now the projecting and downwards and release it quickly . You will notice that plastic ruler starts vibrating and at the same time a sound is heard .

tuning forkWhat is a tuning fork ?A tuning fork is a U-shaped steel fork provided with a steel handle. The two arms of the turning fork are called prongs, whereas the handle is called stem. It is a convenient source of producing sound vibrations in a laboratory.

ActivityAn experiment to prove that sound produced by tuning fork is due to the vibrations of prongs.

Take a small Thermocol ball and suspend it from an iron stand with a light silk thread . Strike one of the prongs of the tuning fork on the hard rubber pad and bring it close to your ear. You will be able to hear the sharp humming sound of the tuning fork. Now, touch one prong of he tuning fork to the thermocol ball. It will be observed that thermocol ball flies outward.

Definitions Amplitude : The maximum displacement of a

vibrating body from its mean position is called its amplitude.

Frequency : The number of vibrations produced by a vibrating body in one second is called frequency.

Time Period: The time that a vibrating body takes to complete one vibration is called its time period.

Unit of frequency: The unit of frequency in si system is hertz.

vibrationVibration is a mechanical phenomenon whereby  oscillations  occur about an  equilibrium point. The word comes from Latin  vibrationem 

Infrasonic : if the frequency of the vibration is less than 20 Hz then the human ear cannot preserve them such vibration are known as infrasonic vibration .

Sonic : if the frequency of the vibration is between 20 & 20000 Hz is called sonic vibration .

Ultrasonic : if the frequency of the vibration is more than 20000 Hz then the human ear cannot preserve them such vibration is called ultrasonic vibration.

ActivityAn activity to prove sound travels through solids .

Close the doors and windows of your dining room . Place an alarm clock at one end of the dining table . Stand at another end of the table and try to hear ticking of alarm clock .

you will be able to hear faint ticks as the sound travels through air . Now place your ear on the table and again listen . You will be able to hear the ticking of alarm in much louder and clear voice .

Human ear Our ear is a kind of devise which helps to hearer sounds produced around us . human ear

Outer ear Middle ear Inner ear

outer earIt consists of a flat like structure called pinna . It is further connected to ear canal , at the end of which Is a circular membrane called eardrum .

The pinna collects the sound waves and then directs them through ear canal . The sound waves , on striking the ear drum make it vibrate exactly the same way as the given sound emitting object is vibrating .

middle earIt consists of a chain of three bones , which on one side are connected to ear drum and on the other side to the inner ear. When the ear drum vibrates, the bones in the middle ear start vibrating. Thus the bones help in magnifying the vibrations of the ear drum.

Inner earThe inner ear consists of two parts:

1}Cochlea : it is a spiral tube lined with sensory receptors , which are connected to the sensory nerve. The sensory nerve is connected to the brain.

2}semicircular : they are not connected to hearing but helps us to balance in three dimensions . The feeling of up , down , sideways etc is controlled by the semicircular canals .

PitchWhat is a pitch ?Pitch is the effect produced in the ear due to the sound of some particular frequency . Pitch depends upon the frequency of a vibrating body , i.e., the higher the pitch the less is the frequency .

The sound produced by a flute is more shrill than the sound produced by a table or a drum .

Difference between loudness and pitch

loudness

Loudness depends upon the extent of amplitude of the vibrating body.

The more the energy received the louder the sound .

Loudness does not change with the change in frequency.

pitch Pitch is the effect produced in the brain by the sound of some particular frequency .

Pitch does not depend upon the amount of energy received by the ear.

Pitch changes with the change in frequency.

Difference between musical sound and noise

musical sound

It has a pleasing effect on the ears .

It is produced by regular periodic vibration in a material .

The amplitude of vibration and its frequency do not change suddenly .

noise

It does not have a pleasing effect on the ears .

It is produced by irregular vibration in a material .

The amplitude of vibration and Its frequency change suddenly.