Sound Class 8 Science Chapter 10 Notes

Sound Class 8 Science Chapter 10 Notes are available here. These notes are prepared by the subject experts of our team.

You recognize the end of a school period by specific sounds or signals.
The sound of knocking or a doorbell indicates someone is at the door.
Approaching footsteps can signal someone’s presence.
In hide and seek, the blindfolded person guesses the closest player by sound.
Sound is crucial for communication and is present in various forms in our surroundings.
List the different sounds you hear around you.
Musical instruments in the school’s music room produce distinct sounds.
The chapter will explore how sound is produced, travels, is heard, and why some sounds are louder than others.

Sound is produced by a vibrating body.
Touching a school bell when it’s not in use versus when it’s producing sound can reveal its vibrations.
Vibration is the to and fro or back and forth motion of an object.
A tightly stretched band produces sound when plucked and stops producing sound when it stops vibrating.
Vibrations produce sound, and in some cases, these vibrations are visible, while in others, the amplitude is too small to see but can be felt.
Instruments like manjira (cymbals), ghatam, noot (mudpots), and kartal produce sound when beaten or struck.

Speaking loudly, singing, or buzzing produces vibrations felt in the throat.
In humans, sound is produced by the voice box (larynx).
The voice box is located at the upper end of the windpipe and contains two vocal cords.
The vocal cords are stretched across the larynx, leaving a narrow slit for air passage.
Sound is produced when air from the lungs forces through the slit, causing the vocal cords to vibrate.
Muscles attached to the vocal cords can adjust their tightness, affecting the type or quality of voice.
Tight and thin vocal cords produce a different voice quality compared to loose and thick cords.
Vocal cord length varies: about 20 mm in men, 15 mm in women, and even shorter in children.
The differences in vocal cord length result in different voice qualities among men, women, and children.

Sound needs a medium to propagate or travel.
When you call a distant friend, sound travels through the air to reach them.
Decreasing air in a tumbler leads to decreasing loudness of a sound, implying air’s role in sound propagation.
In a vacuum, sound cannot travel, demonstrating the need for a medium.
Sound can travel through liquids, solids, and gases.
An example activity to show sound traveling through a solid is placing your ear on one end of a table while someone scratches the other end.
Making a toy telephone with strings illustrates sound traveling through strings.

We hear sound through our ears.
The outer part of the ear is shaped like a funnel, guiding sound into the ear canal.
Sound travels down the ear canal to the eardrum, a thin stretched membrane.
The eardrum vibrates when sound vibrations hit it, similar to a stretched rubber sheet.
The eardrum sends these vibrations to the inner ear.
From the inner ear, the signal is transmitted to the brain.
This process allows us to hear sound.

Vibration (to and fro motion) is also known as oscillatory motion.
The number of oscillations per second is called the frequency of oscillation.
Frequency is measured in hertz (Hz), with 1 Hz equal to one oscillation per second.
Example: An object oscillating 20 times per second has a frequency of 20 Hz.
Amplitude and frequency are key properties that make sounds different and recognizable.
Sounds can be differentiated based on their amplitudes and frequencies.

The loudness of sound depends on its amplitude; larger amplitudes produce louder sounds, while smaller amplitudes produce feeble sounds.
Even if two sounds are equally loud, they can differ in other ways.
Frequency determines the pitch or shrillness of a sound; higher frequencies result in higher-pitched sounds, while lower frequencies produce lower-pitched sounds.
Examples: A drum produces a low-pitched sound due to its low vibration frequency, while a whistle produces a high-pitched sound due to its high frequency.
Different animals, like birds and lions, produce sounds with varying frequencies and pitches.
Children’s voices generally have higher frequencies than adults’ voices.
Women’s voices typically have higher frequencies than men’s voices.

A vibrating body is needed for the production of sound.
Not all vibrating bodies produce sounds that are audible to the human ear.
Sounds with frequencies less than 20 Hz are inaudible to humans.
Sounds with frequencies higher than 20,000 Hz (20 kHz) are also inaudible to humans.
The range of audible frequencies for humans is roughly from 20 Hz to 20,000 Hz.
Some animals, like dogs, can hear sounds with frequencies higher than 20,000 Hz.
Police use high-frequency whistles that dogs can hear but humans cannot.
Ultrasound equipment operates at frequencies higher than 20,000 Hz and is used for medical investigations and tracking.

We hear different types of sounds around us.
Some sounds are pleasing, while others cause discomfort.
Unpleasant sounds, like those from construction sites or vehicle horns, are called noise.
If all students in a classroom speak together, the resulting sound is considered noise.
Musical sounds, such as those from a harmonium or sitar, are pleasing to the ear.
Even musical sounds can become unpleasant if they are too loud.

Excessive noise in the surroundings can cause health problems.
Noise pollution can lead to lack of sleep, hypertension (high blood pressure), anxiety, and other health disorders.
Continuous exposure to loud sounds can result in temporary or permanent hearing impairment.

To control noise pollution, we must control the sources of noise.
Silencing devices should be installed in aircraft engines, transport vehicles, industrial machines, and home appliances.
Noisy operations should be conducted away from residential areas.
Noise-producing industries should be set up away from residential areas.
The use of automobile horns should be minimized.
TV and music systems should be operated at low volumes.
Planting trees along roads and around buildings can reduce the harmful effects of noise pollution by cutting down on the sounds reaching residents.

Total hearing impairment is rare and usually present from birth.
Partial hearing impairment often results from disease, injury, or age.
Children with impaired hearing need special care and can communicate effectively by learning sign language.
Hearing loss in children can lead to defective speech since speech develops as a direct result of hearing.
Technological devices can improve the quality of life for the hearing-impaired.
Society can improve the living environment for the hearing-impaired and help them live normal lives.

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