Grade 8, Physics
- π Introduction to Sound Energy
- π Vibrations and Tuning Forks
- π How Sound Travels
- ποΈ Characteristics of Sound: Pitch, Loudness, Quality
- π Human Ear: Structure and Function
- πΆ Audible and Inaudible Sound
- π€ Music Industry and Sound
- π Reflection of Sound and Echos
- π Ultrasonography and Medical Applications
- ποΈ Golconda Fort Echoes
- π€ Robots and Sound Sensors
- π Noise vs. Music: Understanding Noise Pollution
- π Measures to Reduce Noise Pollution
- π Hearing Impairment and Solutions
- π Fun Fact: Sign Language Gloves for Communication!
- Sound is a form of energy that produces a sensation of hearing in our ears
- Vibration is a rapid back and froth movement of an object about its mean position.
- Sounds produced because of vibration
Tuning fork:
- Tuning fork is a U shaped single Steel piece with handle.
- Two arms of tuning for called prongs and handle is called stem
- It is a convenience source of producing sound vibrations in lab.
How do sound travels??
- Sound is produced by vibration of object
- Vibrating object produced sound in the form of energy
- Vibrating object transfer this energy to air molecules close to it
- These air molecules start vibrating back and froth with same frequency
- These vibrating air molecules pass on their vibrations next to air molecules
- This process goes on all the air molecules around the sound producing object start vibrating back and forth.
- When vibrating air molecules fall on ear drum we feel vibrations as sound.
Define Medium??
- The substance or matter through which sound is transmitted is called medium
- Medium can be solid liquid or gas
- Sound cannot travel in vaccum
Speed of the sound:
- The speed with which sound waves travel depend on the nature and the density of the medium.
- Speed of the sound changes with atmospheric conditions like temperature, atmospheric pressure, humidity etc
Speed of the sound in
- Solid – Steel 5960 m/s
- Liquid – Distilled water – 1498m/s
- Air – 340 m/s
- Hydrogen – 1284 m/s
Sound travels in the form of waves
Waves are characterized by frequency amplitude and time period
Simple pendulum
It consist of a small metal Bob suspended by long thread from a rigid support so that bobs free to swing back and froth.
One oscillation of pendulum
Motion of Bob of pendulum from one extreme position to other extreme position and back is called one oscillation of pendulum
Amplitude of pendulum
- The maximum displacement of Bob from its mean position on either side is called amplitude of pendulum.
- When object oscillates in air amplitude of oscillation gradually decreases due to resistance of air
Time period of pendulum
- Time taken by Bob of pendulum to complete one oscillation is called time period of pendulum
- As long as amplitude of oscillation is small pendulum takes equal intervals of time to complete each oscillation
- It is denoted by ‘T’ in seconds
Frequency:
- The number of complete oscillations made by a simple pendulum in 1 second is called its frequency.
- SI unit of frequency is Hertz.
- It is denoted by ‘n’ or ‘f’
- A frequency of one Hz is one oscillation per second.
- When simple pendulum makes four oscillations in 1 second then its frequency will be 4Hz.
What are the various characteristics of sound??
- Pitch
- Loudness
- Quality
Define Pitch??
- It is a characteristic of sound it is used to distinguish shrill sound from grave sound though they have same loudness.
- It is a Subjective measurement
Distinguish between grave sound and Shrill sound??
Grave sound | Shrill sound |
Pitch of the sound produced by an object vibrating with low frequency is called low and sound is called grave or flat sound. | Pitch of the sound produced by object vibrating with high frequency is high and the sound is called Shrill sound |
Low frequency low pitch grave sound | High frequency high pitch Shrill sound |
Example Men have large vocal cords vibrate with low frequency | Example Women and children have short vocal cord therefore vibrate with high frequency to produce shrill sound. |
Other examples
- Wings of bee and mosquito vibrate with high frequency and produce shrill and high pitch.
- Pleasant sound of different pitches are produced by Jal Tarang
- Skin of tabla or guitar of strings tightened to give high pitch
Loudness
- Loudnesses characteristic of sound by which loud sound can be distinguished from same to sound even though when they have same pitch
- Loudnesses directly proportional to the square of amplitude of vibration producing sound
- Smaller amplitude soft sound
- Larger amplitude loud sound
What are the factors affecting loudness ??
- Surface area of vibrating object
- Distance from vibrating object
- Density of medium
- Motion of medium
- Loudness of sound is measured in decibels (dB)
- Example very faint sound rustling of leaves whispering 20 decibels
- Very loud sound heavy traffic 90 decibels
- Dangerously loud rocket take off 200 decibels.
Quality:
- It is characteristic of sound that enable us to distinguish between two sounds of same pitch and loudness produced by two different sources
- It depends upon the waveform of sound
- Quality of sound is called its tone
- Some vibrating object produce sound of single frequency example tuning fork
- Some vibrating object do not produce sound of single frequency but also other frequencies example guitar or sitar
- They produce sound of single frequency called basic or fundamental frequency
- Along with that they produce mixture of sound of other frequency called harmonics .
- Harmonics give richness to the sound.
Sound produced by Humans:
- Sound is produced by the voice box of the larynx
- It is at the upper end of the windpipe
- Two ligaments called vocal cords are stretched across the voice box/ larynx, it leaves a slit between them for the passage of air.
- When lungs force air through slit, vocal cords vibrate resulting in production of sound.
- When the vocal cords are loose and thick, the sound produced is of low pitch/ frequency.
- When the vocal cords are tight and thick, the sound produced is of higher pitch / frequency.
- Men have longer vocal cords than women and children.
- Frequency of sound produced by women and children is higher than men.
Structure and working of Human Ear
When sound propagating through air reaches ear, we hear it. Our Ear is divided into
- Outer Ear
- Middle Ear
- Inner Ear
Outer Ear:
- It consist of flap like cartilaginous structure called Pinna.
- It collect sound waves.
- Pinna is connected to ear canal, at the end Ear drum is present
- Ear drum ( Tympanic Membrane ) is a streched membrane that separates outer Ear from the middle ear.
Middle Ear:
- It has 3 bones Hammer, Anvil, Stirrup
- Hammer is connected to ear drum and striuup is connected to inner ear.
- Three bones are collectively called Ossicles.
- Middle ear is connected to throat through Eustachian tube.
Inner Ear:
- Inner ear consist of cochlea and semi circular canals.
- Cochlea is a coiled tube looks like snail shell
- It is filled with fluid and has many hair cells inside it
- The receptors send impulses through sensory neurons to auditory nerve, that connects inner ear to brain
Working of Human Ear
- Pinna collects sound waves from surrounding send them to ear drum through ear canal.
- When sound wave fall on ear drum, it starts to vibrate.
- Three bones ( Hammer, anvil, Stirrup) receive vibrations from ear drum and amplify it.
- Cochlea receives amplified vibrations from three bones.
- Sensitive hair cells present in cochlea convert them into nerve impulses.
- Nerve impulses are carried to brain through auditory nerve
- Brain decides nerve impulses into specific sound
Audible and Inaudible sound:
Audible sound:
Sound whose frequency lies between 20Hz and 20,000 Hz which we are able to hear is called audible sound.
Infrasonic sounds:
- Sounds ( Inaudible for humans) having frequency less than 20 Hz are known as Infrasonic sounds
- Ex: Rhinoceros can communicate with frequency less than 5 Hz. Whales and elephants hear infrasonic sounds.
- Low frequency infrasonic sounds are produced before main shockwaves during earthquakes. This sound can be heard by animals, they make alert and show abnormal behaviour.
Ultrasonic sounds:
Sounds ( Inaudible for humans) having frequency more than 20,000 Hz are known as Ultrasonic sounds.
Reflection of sound:
- When sound strikes a hard surface, it gets reflected
- Reflection of light follows laws of reflection that is, angle of incidence is equal to angle of reflection
- Sound do not require smooth polished surface for reflection
- Sound waves spread in air in all directions
- In small rooms, original and reflected sound waves reach our ears at same time.
Distinguish between Good and Bad reflectors??
Good reflectors | Bad reflectors |
Objects that are hard and have smooth surface are called good reflectors of sound waves. | Objects which are soft and porous are called bad reflectors of sound |
Ex: Metal, Metal alloys, Steel, Concrete, brick walls dense materials | Ex: Clothes, curtains, paper, wood, thermocol, asbestos sheet |
They are bad absorbers of sound | They are good absorbers of sound |
Music Industry and Sound :
- In music recordings studios, sound absorbing materials are used in wall, to prevent disturbance of outside sound.
- Ceiling, floor and walls of cinema halls, auditorium are covered with tiles, curtains and carpets. Because they are good absorber of sound, so it is possible to hear clear sound from speakers.
Echo
- Echo is the repetition of the original sound, after the sound reflected from a distant dense and rigid object. Example high buildings ,cliffs etc.
- The reflected sound which can be heard distinctly after the lapse of 0.1 second from original sound by human ears is called echo.
- Speed of the sound in air is 340 m/s
- Minimum distance for echos 17 m
Essential requirement for echo:
1. Minimum distance between the source of sound and reflecting surfaces is 17 m.
2. Sound does loud enough to be heard after reflection
3. That should be a high building or hill acting as a reflecting surface
Ultrasonography
- Echos used by the doctors to study the internal organs of the body
- Ultrasonic vibrations reflected by different organs helps the doctor to make the image of the organ
- This technique is used to study unborn baby inside the mother’s Womb
- This technique when used to study the heart it is called Echo cardiography.
Golconda fort near Hyderabad
If one claps at a particular point under dome echos are heard in the Durbar hall the highest point of fort about a kilometre away.
- Robots detect sound through sensors. They are microphones.
- Microphones detect the sound and generate voltage proportional to volume of sound.
- Ultrasonic sensors in robots helps to detect nearby objects.
- Sensor emit ultrasonic pulse that is captured by receiver.
Difference between Noise and Sound??
Noise | Music |
1. Unwanted, unpleasant very loud sounds are Noise | 1. Pleasant and soft sounds are called Music |
2. Long exposure to Noise lead to serious health hazards. | 2. It does not cause any health hazards. |
3. Noise is produced by irregular and Non periodic vibrations | 3. Music is produced by regular and periodic vibrations |
4. Ex: Sound from Factories, loudspeakers in functions. | 4. Ex: Music from musical instruments like Sitar, Piano, Guitar etc. |
Musical Instruments
Depending on the way, the air vibrates in them there are 5 musical instruments
- Stringed
- Wind
- Percussion
- Reed
- Ghana vadya
String Instruments
- Music is produced by vibrating string. When strings are plucked, struck/played with bow, they vibrate to produce musical sound.
- These instrument have hollow air chamber that helps to increase the loudness of sound produced.
- Ex: Veena, Sitar and Violin
Wind Instrument
These instrument are in form of pipe, when you blow in air into them, the column of air vibrates producing note that is sound of particular frequency. Ex: Whistle, Bungle, Saxophone, Trumphet
Percussion instruments
Vibrating skin/membrane produces sound. Ex: Drum, Dholak, Mridangam
Reed instruments
They contain metal reeds which produce sound when air is blown through them. Ex: Harmonium, Mouthorgan
Ghana vadya
Musical instrument Manjira ( Crybals) Tarang simple beaten or struck to produce musical sound. Ex: Tarang, Ghatam ( Mudpot), Khartal
Noise pollution
Noise
Noise from any source that cause disturbance or discomfort of any kind of environment is called Noise pollution
Sources of Noise pollution
- Loud music system,
- Crackers,
- Excessive horns
- Moving aeroplane, train, loudspeakers etc.
Harmful effects:
- It causes nervous tension, irritation, headache,
- Earache, high blood pressure
- It causes lack of concentration in work/ studies
- It disturbs night sleep
- Prolonged exposure to Noise affect eardrum and lead to temporary/ permanent loss of hearing
Measures to reduce Noise pollution
1. Automobiles fitted with silencers/soft horn
2. Horns of vehicles should not be blown unnecessarily mainly near hospitals, schools etc.
3. Do not play radio, TV and sterosystem to loudly.
4. Airports and Noise making factories should be shifted away from residential areas of city.
5. Use of loudspeaker at social/ religious fiction should be restricted.
6. Do not play loud music in cars and other vehicles while driving
7. Machine should be properly maintained to reduce noise pollution
8. Avoid crackers that makes loud noise
Hearing Impairment
1. When a person cannot hear properly or has lost hearing ability it is said to be hearing impaired
2. Some people are born with very poor hearing. This is called Total Hearing Impairement
3. Deaf people use sign language with their hands to communicate with others effectively
4. Partial hearing loss, occurs due to illness, ear infection,injury,old age/noise pollution
5. This can be rectified using hearing aids
Fact:
Ukrainian students developed gloves fitted with sensors, gyroscope, accelerometers that can translate sign language into text and then into spoken words using text to speech machine. Whole system is connected to smartphone over Bluetooth
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